(TO TABLE OF CONTENTS)ULTRASOUND IN PREGNANCY:
A Web Book for Parents and Parents-to-Be
by Michael Applebaum, MD, JD, FCLM
Dr. Applebaum's FitnessMed.com
Dedication
Why This Book?
How to Use This Book
Is Ultrasound Safe
During Pregnancy?
How Does Ultrasound Work?
The Ultrasound Equipment
How is an Ultrasound
Performed?
Your Ovaries
Your Uterus
Fibroids
The Parts of a Pregnancy
The Placenta
How Far Along is My
Pregnancy?
When Should the
Heartbeat be Detected?
When Does the Fetus Begin to Move?
How Long is the Fetus/Embryo
and How Much Does It Grow (Length)?
How Much Does the Fetus/Embryo Weigh?
When Can the Gender of the
Fetus be Determined?
The
MSAFP, MSAFP-PLUS or "Triple Test" Blood Tests
The Level II Ultrasound
How Many Ultrasounds Do I
Need?
The
Trimesters -- How Long is a Pregnancy?
Specialized Ultrasound
Examinations
For me, there are few things more enjoyable than sharing the happiness parents-to-be feel when they see their baby, still in the womb. Or experiencing the excitement parents-to-be feel when they hear the embryo’s/fetus' heartbeat or see their embryo/fetus move before it is felt.
Ultrasound is a miracle. The fact that we possess the capability to see into the uterus and image life before birth is mind-boggling.
Who could have dreamed, slightly more than a decade ago, that today we would not only see the embryo and fetus, but also the architecture of its organs? And much more.
Virtually no interaction in Medicine is as rewarding to me as seeing the unseen and bringing the joy of a new life to those who have created it.
This book is dedicated to the many who have shared their pregnancies with me and trusted me to share it with them.
It has been my good fortune to perform ultrasound examinations on many women during their pregnancies.
Experience has taught me that most of my patients (and their significant others) have questions about ultrasound during pregnancy. A lot of these questions arise from their apprehension of the unknown. It has been apparent to me, that if these questions were answered prior to the ultrasound, the experience would be much more pleasant.
The purposes of this book are to:
1. help make the pregnancy ultrasound an enjoyable experience
2. answer the most common questions people have about ultrasound in pregnancy
3. teach the reader about the pregnancy and the changes the embryo/fetus is undergoing
4. demonstrate to the reader some of what can be accomplished by an experienced scanner (one who performs an ultrasound examination or "scan.")
Read this book, find out and SEE what is happening inside you during your pregnancy.
There are diary pages in the back for you to fill in to keep a log of your pregnancy and ultrasounds.
TIP! -- If you hyperlink to another section of the book to benefit from the hypertext features, click the "BACK" button of your browser to return to your previous location.
USING THE GLOSSARY -- in the text, almost all occurrences of the words in the Glossary are hyperlinked to the Glossary. I did this so people who are reading this book out of sequence can get the definitions as needed. Also, people who are reading this book multiple sittings will have opportunities to refresh their memories. If you are reading this book in one sitting or in big chunks you may find it frustrating if you hyperlink to the Glossary over and over again. To avoid this, check to if the link leads to the same place by looking at your browser's information area.
REMEMBER! -- This book is not a substitute for medical advice from your physician. Always consult directly with your physician regarding any and all issues/questions you may have about your pregnancy.
The Number One Question.
The Answer: YES!
The following, is a quotation from the American Institute of Ultrasound in Medicine addressing this very question:
AMERICAN INSTITUTE OF ULTRASOUND IN MEDICINE
Official Statement
Approved
March 1993
October 1982
Diagnostic ultrasound has been in use since the late 1950s. Given its known benefits and recognized efficacy for medical diagnosis, including use during human pregnancy, the American Institute of Ultrasound in Medicine herein addresses the clinical safety of such use:
No confirmed biological effects on patients or instrument operators caused by exposure at intensities typical of present diagnostic ultrasound instruments have ever been reported. Although the possibility exists that such biological effects may be identified in the future, current data indicate that the benefits to patients of the prudent use of diagnostic ultrasound outweigh the risks, if any, that may be present.
The Bottom Line: as far as anyone can tell, and a lot of people have looked, ULTRASOUND IN PREGNANCY IS SAFE FOR BOTH THE MOTHER AND EMBRYO/FETUS.
Basically, the ultrasound machine sends out a beam of sound for a really short period of time. Then it listens for echoes.
Think about this example. You are in a big, empty room. You yell and then you listen. You hear an echo as the sound bounces off the walls. In other words, when you send out a sound beam (the yell) and then listen, you hear an echo. The further the wall is from you, the longer it takes for the echo to return to you. The closer the wall is to you, the sooner you hear the echo.
The ultrasound machine does the same thing. And more. It uses the sound it hears to create the picture you see on the monitor. How?
Every time it hears an echo from the sound beam it sent out, it places a dot (usually a shade of gray, ranging from black to white) on the monitor. The location of each dot depends on how long it takes the echo to reach the machine (i.e., how long the machine has to wait until it hears the echo). The shade of gray is determined by how strong (loud) the machine perceives the echo to be.
Picture it this way. An echo from a wall with a hard, smooth surface will be louder than an echo from a wall with a soft, bumpy surface.
Therefore, a strong echo from deep inside the mother will be whiter and farther from the top of the monitor screen. A weak echo from less deep inside the mother will be more gray and closer to the top of the monitor screen.
The ultrasound machine sends out a sound beam and listens for echoes many times a minute in order to create the image on the screen.
There are essentially three parts that are of practical interest:
1. The TRANSDUCER
2. The MONITOR
3. The MACHINE ITSELF
THE TRANSDUCER -- This is the component the person performing the ultrasound examination holds in his/her hand. Within it is a crystal that emits the ultrasound beam and then "listens" for the echoes.
The examiner moves the transducer to aim the ultrasound beam towards the area he/she wants to examine.
THE MONITOR -- What every patient is most interested in. The monitor is a TV screen that displays the images created by the machine.
THE MACHINE ITSELF -- This contains the computer power to transform the echoes the transducer "hears" into the images you and the examiner see on the monitor.
In Obstetrics, there are two commonly employed methods for performing an ultrasound examination:
1. Transabdominal
2. Transvaginal (also called Endovaginal)
The TRANSABDOMINAL method is the older of the two and the one with which most people are familiar. After applying gel or oil to the abdomen, the examiner moves the transducer on the belly in order to image the areas of interest.
The reason gel or oil is applied first, is to help facilitate the transmission of the sound beam from the transducer to the skin.
This examination is performed while the patient has an optimally filled bladder.
The reason you need a properly filled bladder is because the ultrasound beam does not travel well through the gas in the intestines. The filled bladder helps move your intestines out of the way. That's why your doctor will request that you drink fluid before your examination and not go to the bathroom to empty out until he/she has had a chance to examine you.
Incidentally, the reason I said "an optimally filled bladder" and "a properly filled bladder," but not a full bladder, is because, sometimes there can be too much fluid in the bladder and the examiner may ask you to empty some out.
"Only some?" you must be thinking. Yes. This is called incremental voiding and it can make all the difference in the world between a great and a lousy scan. It may sound difficult, but, believe me, in my experience, thousands of women have done it with no difficulty at all. Although not all examiners believe in incremental voiding, I think it is one of the most important techniques used for performing high quality ultrasound examinations.
TRANSVAGINAL ultrasound is generally performed with the bladder empty. This type of examination is performed with a specially designed ultrasound probe (transducer) that is placed in the vagina, just like a tampon. Most people find this method more comfortable than a transabdominal scan.
With this method, the examiner can generally visualize structures more clearly and with greater resolution because he or she is looking a lot closer than by the transabdominal route. The only limitation to this approach is distance. For technical reasons, the ultrasound beam from the transvaginal probe does not travel as far into the body as the ultrasound beam from the transabdominal probe. Therefore, because the uterus has not enlarged very much, transvaginal sonography is usually confined to the first trimester, but may be useful later on in pregnancy.
TRANSVAGINAL SONOGRAPHY IS ALSO CONSIDERED TO BE A SAFE PROCEDURE WITH NO HARMFUL EFFECTS TO EITHER THE MOTHER OR THE EMBRYO/FETUS.
There is also a third technique used in Obstetrical (and Gynecological) ultrasound. This is the Transperineal approach. In essence, this can be considered as a cross between the endovaginal and transabdominal approaches. A transperineal scan is performed by placing the transabdominal probe against the skin just below the vulva. The probe is not inserted into the vagina. As with the transvaginal approach, the examination is generally performed with the bladder empty; however, an optimally distended bladder is not always an empty bladder. This type of scan is used to image the cervix. It can also be used to visualize structures inside the uterus which are close to the cervix. Transperineal scanning is a very useful technique when used in the proper circumstances.
I have to mention something about the ovaries, because almost everyone is surprised to find out that during pregnancy a cyst is usually present within at least one ovary.
THIS IS ALMOST INVARIABLY NORMAL.
You must be wondering "Why is there a cyst in my ovary?"
The egg, which comes from the ovary, needs someplace to grow until it is mature enough to be released in order to meet up with a sperm and get fertilized. The place in which it grows is a fluid-filled sac within the ovary called a CYST or FOLLICLE. More than one cyst may develop during the menstrual cycle, but, in general , only one attains maturity and ruptures. This is called the GRAAFIAN FOLLICLE.
After the Graafian follicle ruptures, releasing the egg, it begins to serve another function. It produces progesterone, a hormone. This hormone provides the environment necessary for the early pregnancy to develop. (Later, the placenta secretes the hormones). The ruptured Graafian follicle is given another name, the CORPUS LUTEUM CYST. To see an image of a normal corpus luteum, click here. Using a 14.4 modem, this will take about 60 seconds to load.
A corpus luteum cyst may be present and visible by ultrasound for months into the pregnancy, even though it ceases to function before the end of the first trimester.
The uterus is the womb. That is, the organ in which the pregnancy develops. Specifically, the pregnancy develops in the lining tissue called the endometrium. The endometrium is surrounded by muscle called myometrium.
After fertilization, which occurs in the Fallopian tube, the embryo travels into the endometrial canal and implants into the endometrium where it begins to develop.
Fibroids are also known as MYOMAs.
A fibroid is a growth of the muscles of the uterus.
Fibroids, or myomas, are almost always BENIGN.
In general, the hormonal changes that the mother-to-be’s body undergoes, promote the growth of fibroids. Thus, previously unseen or undiscovered fibroids may become apparent during early pregnancy. However, as the pregnancy develops past the first trimester, it may become more difficult to visualize them. Usually, however, most significant myomas can be detected sonographically.
Fibroids infrequently cause problems during a pregnancy.
The significance of a fibroid is determined by its size, location and any problems it may be causing (e.g., frequent urination, pain, a sensation of fullness, etc.). For example, relatively large fibroids (myomas) that are located at the top or sides of the uterus may cause no problems at all. But, much smaller fibroids located adjacent to the developing gestational sac or along the path of the birth canal may affect the pregnancy.
Usually, fibroids can be detected with ultrasound.
If you have fibroids, ask your physician if he/she expects any problems because of them.
Now that you are pregnant, just what is inside of you?
A pregnancy contains things inside of other things inside of still other things. Its a lot like those dolls where a large doll contains a smaller doll, which in turn contains a smaller doll, etc.
So, going from the outside in:
1. The uterus (described in the previous chapter)
2. The placenta
3. The chorion (or chorionic membrane)
4. The yolk sac
5. The amnion (or amniotic membrane)
The PLACENTA, is derived from tissue called TROPHOBLAST.
Simply stated, the placenta surrounds the entire pregnancy early on. As the pregnancy progresses, the placenta only surrounds a portion of it. This is normal.
The placenta allows substances to pass from the mother to the embryo/fetus and from the embryo/fetus to the mother. It also produces hormones which help support the pregnancy. To see an image of an early pregnancy with placental tissue surrounding it completely, click here. Using a 14.4 modem, this will take about 50 seconds to load.
The CHORION, is the membrane upon which the placenta sits. I find that the best way to visualize it is as follows:
If the placenta was a shag carpet (which it actually looks like when magnified!), then the chorion is the carpet backing. The chorion is not normally seen as a separate structure during an ultrasound examination.
The YOLK SAC sits between the chorion and the amnion. It is attached to the embryo/fetus by the VITELLINE DUCT. (Vitelline comes from the Latin word vitellus which means "little calf.") The cells which form the blood cells of the embryo migrate from the yolk sac to the embryo. It is believed that the yolk sac ceases functioning when the embryo is about eight weeks old. It can still be seen by ultrasound later than that, however.
If the AMNION was a bottle, the embryo/fetus would be the ship inside of it. Actually, the amnion is more like a water balloon with the embryo/fetus inside of it. At first, the amnion is much smaller than the chorion. By the time the fetus is about 16 weeks old, the amnion is about the same size as the chorion; then, they fuse forming the CHORIO-AMNIOTIC MEMBRANE. This can be pictured as similar to an inner tube filling a tire. To see an image of the Amniotic Membrane, click here. Using a 14.4 modem, this will take about 50 seconds to load.
The GESTATIONAL SAC, also known as the BAG OF WATERS, is essentially everything inside of the chorion (also known as the chorionic sac) during early gestation or everything inside of the chorio-amniotic sac during later gestation (i.e., after approximately 16 weeks menstrual age). To see an image of the Gestational Sac with a Day 48 Embryo, click here. Using a 14.4 modem, this will take about 50 seconds to load.
Is the placenta in the right location?
From the perspective of the embryo and fetus, as long as the placenta is there it is in the right location. Remember, the placenta functions to allow materials (food, oxygen, etc.) to exchange between the mother and the gestation. Obviously, in a continuing pregnancy, the placenta must be there.
From the mother's perspective, unfortunately, there can be a wrong location. This is when the placenta covers the exit from the uterus. This exit is called the internal cervical os. It is the doorway from the uterus to the birth canal. When the placenta is located between the fetus and the birth canal, it is called a placenta previa.
Placenta previa is a diagnosis made by ultrasound. In general it is not diagnosed until after the first trimester.
A placenta previa can affect the pregnancy in several ways. Most commonly, you will require a Caesarean Section for delivery. Also, there is an increased chance that you will experience some bleeding during the pregnancy.
Virtually all complications associated with placenta previa can be successfully handled by your obstetrician.
If a placenta previa is present, talk to your doctor about its effects and your options. To see an image of a placenta previa, click here. Using a 14.4 modem, this will take about 1.0 minute to load.
One last point, and it represents a pet peeve of mine. Where the placenta appears to be located during an ultrasound examination depends on the activity of the uterus. What I mean, is that the uterus is essentially a muscle. Muscles know how to do two things -- contract and relax. When the uterus contracts, which it frequently does whether you are pregnant of not (incidentally, you do not feel these contractions), the placenta may appear closer to the internal cervical os than it really is when the uterus is relaxed. If you have a repeat ultrasound examination to re-evaluate the relationship between the placenta and the internal cervical os the placenta may appear in a different location. Some people will tell you that the placenta "migrated." Personally, I think that is wrong. The placenta did not migrate -- the contraction that was there relaxed.
I know that the preceding paragraph was complicated. Maybe the following example will help. If you flex your biceps, your hand and wrist move closer to your shoulder. If a visitor from another planet were observing you, it/he/she/whatever could say that your hand and wrist are located next to your shoulder. Of course, it/he/she/whatever is wrong. When you relax your biceps, it is apparent that your hand and wrist are at the end of your forearm away from your shoulder. Similarly, a contraction of the uterus can make it appear as if the placenta is near the internal cervical os. But when the contraction relaxes, it is apparent that the placenta is much further away.
An experienced scanner should be able to distinguish between a true placenta previa and the appearance of one due to a uterine contraction.
Physicians determine the age of an embryo/fetus from the date of the first day of the mother's last normal menstrual period (i.e., the first day of bleeding). Why?
Because way back when, before ultrasound, the only objective way to reasonably accurately know where a woman was in her menstrual cycle, was to know the day she began her flow (Day 1). (Conception usually occurs around Day 14, or two weeks into the cycle.)
Consequently, even though we can tell with substantial certainty when conception probably took place, we still give age from the last normal menstrual period. It's a little confusing, but that's the way it is. Forgive us.
Since we use the first day of the last normal menstrual cycle to determine the age of the embryo/fetus, we call this measurement MENSTRUAL AGE.
For example, if conception occurred 8 weeks before an ultrasound scan, we would say that the fetus is 10 weeks old menstrual age. (remember, conception occurs approximately 2 weeks after the first day of the menstrual period.)
Incidentally and interestingly, conception may not occur on the day of intercourse. It may occur within several days of intercourse. This is due to the fact that the sperm and egg may take some time to find each other and the sperm can live for several days within a woman.
The age of a pregnancy is determined in different ways at different times during gestation.
Before an embryo is visible, but the sac in which it will grow (the gestational sac) is visible, a measurement called the MEAN SAC DIAMETER (MSD) is used.
The MSD is obtained by measuring the gestational sac in its three largest perpendicular dimensions, adding those values and dividing by three.
Once the embryo becomes visible, the measurement used to determine age is the CROWN-RUMP LENGTH (CRL).
To obtain the CRL, one measures from the top of the head to the tip of the butt. To see images demonstrating the fetal crown and rump, click here. Using a 14.4 modem, this will take about 70 seconds to load.
By the time the fetus reaches 12 weeks of age, we use measurement of the BIPARIETAL DIAMETER (BPD) to determine age. The parietal bones are parts of the skull. They are located at the sides of the head. To obtain a BPD, we measure across the skull, from side to side.
By sixteen weeks of age, almost everybody measures two other things, in addition to the BPD, to determine fetal age. These are the FEMUR LENGTH (FL) and the ABDOMINAL CIRCUMFERENCE (AC).
The femur is the thigh bone. The bone between the knee bone and the hip bone.
The abdominal circumference is the distance around the fetal belly.
To determine fetal age, the examiner:
1. measures the BPD, the FL and the AC,
2. determines the age indicated by each and
3. averages them to obtain the fetal age.
So how accurate are we when we tell you how old the embryo/fetus is?
Very accurate early on...less accurate later on.
From 5 - 6 weeks our range is +/ - 4 days.
From 7 - 11 weeks our range is +/ - 5 days.
From 12 - 16 weeks our range is +/ - 7 days.
From 17 - 26 weeks our range is + - 10 days.
From 27 - 28 weeks our range is +/ - 2 weeks.
From 29 - 40 weeks our range is +/ - 3 weeks.
Why are we less accurate as the pregnancy gets older? Think of fetal development as a race in which all the participants are normal. Everybody is at the starting line at the same time. As the race progresses, some pull ahead and others stay behind. At the starting gun, all the racers are bunched together. One mile into the race, the racers are spread out. Two miles into the race, the racers are more spread out. The longer the race, the farther out the field is spread. All the racers are normal, some just race faster, some race slower. Likewise with development. As the gestation progresses, taller fetuses get taller, bigger fetuses get bigger, etc. Just like normal people come in a variety of sizes and shapes, so do normal fetuses.
REMEMBER, fetal development is not a race. A bigger fetus does not necessarily mean better. A smaller fetus does not necessarily mean worse.
WHEN WILL I DELIVER?
Normally, the overwhelming majority of women deliver within +/- two weeks of their expected due dates.
As you may recall from the preceding chapter, the earlier in pregnancy an ultrasound examination is performed, the more accurate it is. Therefore, an expected due date based upon an earlier ultrasound is more accurate than one based upon a later scan.
Okay, here is the most confusing thing to deal with. Suppose that an earlier scan predicts one due date and a later scan predicts another. In general, the first scan is going to be closer to the true due date. Remember that there may be differences in growth rate among fetuses/embryos. These differences become greater and more apparent as the pregnancy progresses.
The first scan, if done well, should always be the most accurate for the purpose of determining the due date.
Using what is called Nagele's Rule is an easy way to estimate your expected due date. It is most accurate if your cycles are 28 days long and you ovulate on Day 14.
Step 1 -- Determine the first day of your LMP
Step 2 -- Add 7 days
Step 3 -- Subtract 3 months
Step 4 -- Add 1 year
If you had either an Artificial/Intrauterine Insemination (AI or IUI), IVF, TET, ZIFT, or GIFT, you can use Applebaum's Rule to estimate your expected due date:
Step 1 -- Determine the date of insemination, IVF, TET, ZIFT or GIFT
Step 2 -- Subtract 7 days
Step 3 -- Subtract 3 months
Step 4 -- Add 1 year
A heartbeat is detectable by 42 days gestational age (six weeks from your last normal menstrual period = LNMP or LMP). This is generally true for a technically adequate ultrasound examination and if the mother is correct about the date of her LNMP. It is usually easier to detect a heartbeat using transvaginal technique than transabdominal technique. As mentioned above, this is due to the fact that the transvaginal ultrasound probe is closer to the embryonal heart.
Please remember, although the embryo may be Day 42 size (six weeks menstrual age), there is still a range of + / - of 4 days. Therefore, do not be discouraged if a heartbeat is not seen when you expect it, especially:
if you are uncertain of your LMP
if your cycles are longer than 28 days
if your menstrual cycles are irregular in duration
If you have any questions, talk to your physician about it.
Not only can a heartbeat be seen by Day 42, it can also be heard using Doppler technique. (Doppler is a technique I will describe later).
WHEN DOES THE FETUS BEGIN TO MOVE?
There is no doubt that the fetus can be seen moving during the eighth week menstrual age. Just because the fetus does not move during a scan, it does not mean that anything is wrong.
In general, the mother feels the fetus move by the eighteenth week. This perception of fetal movement is technically called "quickening." If the placenta is located anteriorly (on the front wall of the uterus), movement may not be felt until later. This is probably because the placenta acts as a cushion between the moving fetus and the mother.
The amount of growth the embryo/fetus undergoes depends on its gestational age. The earlier in gestation, the faster it grows. For example, between six weeks and seven weeks of age, the embryo triples in size. From six to eight weeks it grows about five times bigger. Between seven and eight weeks, however, it grows about 1.6 times its size. The following chart, compares growth from the sixth week on:
LENGTH (approx.) INCREASE IN SIZE
FROM WEEK SIX MENSTRUAL AGE (MA)
| Menstrual Age (MA) | Length (cm) | Length (in) | Growth since six weeks MA |
| 6 weeks | 0.3 cm | .125 in | - |
| 7 weeks | 1.0 cm | 0.4 in | 3 times |
| 8 weeks | 1.5 cm | 0.6 in | 5 times |
| 9 weeks | 2.5 cm | 1.0 in | 8 times |
| 10 weeks | 3.5 cm | 1.4 in | 12 times |
| 11 weeks | 5.0 cm | 2.0 in | 17 times |
| 12 weeks | 6.0 cm | 2.4 in | 20 times |
| 13 weeks | 7.5 cm | 3.0 in | 25 times |
| 14 weeks | 9.0 cm | 3.6 in | 30 times |
| 15 weeks | 10.5 cm | 4.2 in | 35 times |
| 16 weeks | 12.0 cm | 4.8 in | 40 times |
| 17 weeks | 14.0 cm | 5.6 in | 47 times |
| 18 weeks | 16.0 cm | 6.4 in | 53 times |
| 19 weeks | 18.0 cm | 7.2 in | 60 times |
| 20 weeks | 20.0 cm | 8.0 in | 70 times |
| 21 weeks | 22.5 cm | 9.0 in | 75 times |
| 22 weeks | 25.0 cm | 10.0 in | 83 times |
| 23 weeks | 26.5 cm | 10.6 in | 88 times |
| 24 weeks | 28.0 cm | 11.2 in | 93 times |
| 25 weeks | 29.0 cm | 11.6 in | 97 times |
| 26 weeks | 30.0 cm | 12 in | 100 times |
| 27 weeks | 31.0 cm | 12.4 in | 103 times |
| 28 weeks | 32.0 cm | 12.8 in | 107 times |
| 29 weeks | 33.5 cm | 13.4 in | 112 times |
| 30 weeks | 35.0 cm | 14.0 in | 117 times |
| 31 weeks | 36.5 cm | 14.6 in | 122 times |
| 32 weeks | 38.0 cm | 15.2 in | 127 times |
| 33 weeks | 39.0 cm | 15.6 in | 130 times |
| 34 weeks | 40.0 cm | 16.0 in | 133 times |
| 35 weeks | 41.0 cm | 16.4 in | 136 times |
| 36 weeks | 42.0 cm | 16.8 in | 139 times |
| 37 weeks | 43.5 cm | 17.4 in | 145 times |
| 38 weeks | 45.0 cm | 18.0 in | 150 times |
| 39 weeks | 46.5 cm | 18.6 in | 155 times |
| 40 weeks | 48.0 cm | 19.2 in | 160 times |
HOW MUCH DOES THE EMBRYO/FETUS WEIGH?
Until about eight weeks gestational age, the embryo weighs less than a gram. Below is a list of average weights by week of age. More accurate determinations of weight are made in the second and third trimesters by measuring the femur length and the abdominal circumference. This chart is reproduced in the Appendix. In general, male fetuses weigh more than females.
REMEMBER: These numbers are averages. Greater or lesser weights may be perfectly normal and healthy.
WEIGHT (approx.) INCREASE FROM WEEK
EIGHT MENSTRUAL AGE (MA)
| Menstrual Age (MA) | Weight (gm) | Weight (lb/oz) | Weight increase since eight weeks MA |
| 8 weeks | 1.0 gm | 0.035 oz | - |
| 9 weeks | 3.0 gm | 0.11 oz | 3 times |
| 10 weeks | 5.0 gm | 0.18 oz | 5 times |
| 11 weeks | 12.5 gm | 0.44 oz | 12.5 times |
| 12 weeks | 20 gm | 0.7 oz | 20 times |
| 13 weeks | 40 gm | 1.4 oz | 40 times |
| 14 weeks | 60 gm | 2.1 oz | 60 times |
| 15 weeks | 90 gm | 3.2 oz | 90 times |
| 16 weeks | 120 gm | 4.2 oz | 120 times |
| 17 weeks | 170 gm | 6.0 oz | 170 times |
| 18 weeks | 220 gm | 7.75 oz | 220 times |
| 19 weeks | 275 gm | 9.7 oz | 275 times |
| 20 weeks | 330 gm | 11.6 oz | 330 times |
| 21 weeks | 395.5 gm | 13.9 oz | 395 times |
| 22 weeks | 460 gm | 1 lb | 460 times |
| 23 weeks | 555 gm | 1 lb 3 oz | 555 times |
| 24 weeks | 655 gm | 1 lb 7 oz | 655 times |
| 25 weeks | 750 gm | 1 lb 10 oz | 750 times |
| 26 weeks | 850 gm | 1 lb 14 oz | 850 times |
| 27 weeks | 975 gm | 2 lb 2 oz | 975 times |
| 28 weeks | 1100 gm | 2 lb 7 oz | 1100 times |
| 29 weeks | 1260 gm | 2 lb 12 oz | 1260 times |
| 30 weeks | 1420 gm | 3 lb 2 oz | 1420 times |
| 31 weeks | 1585 gm | 3 lb 7 oz | 1585 times |
| 32 weeks | 1750 gm | 3 lb 14 oz | 1750 times |
| 33 weeks | 1915 gm | 4 lb 3 oz | 1915 times |
| 34 weeks | 2080 gm | 4 lb 9 oz | 2080 times |
| 35 weeks | 2250 gm | 4 lb 15 oz | 2250 times |
| 36 weeks | 2420 gm | 5 lb 5 oz | 2420 times |
| 37 weeks | 2660 gm | 5 lb 14 oz | 2660 times |
| 38 weeks | 2900 gm | 6 lb 6 oz | 2900 times |
| 39 weeks | 3075 gm | 6 lb 12 oz | 3075 times |
| 40 weeks | 3250 gm | 7 lb 2 oz | 3250 times |
Until the eleventh week of gestation, males and females appear similar. Even if you took the fetus out of the womb (uterus) and looked directly at it, it would be difficult to tell male from female, at this time. The final appearance of the genitals does not occur until about the fourteenth week.
Ultrasound can reliably determine gender by sixteen weeks gestational age (85% accuracy or better).
You have to understand though, that this is not always easy and the person performing the examination must get "just the right shot." Also, the external genitalia are not very large at this time and sometimes difficult to visualize by ultrasound. To see an image of a male fetus, click here. using a 14.4 modem, this will take about 60 seconds to load.
A full-term pregnancy is defined as 36 weeks in duration or until the fetus weighs 2500 grams. Normal pregnancy can last until 40 weeks.
We tend to talk about development in terms of TRIMESTERs. Each trimester is 3 months in duration.
THE MSAFP, MSAFP-PLUS OR "TRIPLE TEST" Blood Tests
The MSAFP blood test measures the amount of a protein called AFP, or alpha feto-protein, in the mother's blood. It is a screening test that is recommended for all pregnant women. Elevated (high) values are associated with fetal NEURAL TUBE DEFECTS (NTDs) and VENTRAL WALL HERNIAs while low values have been associated with chromosomal abnormalities of the fetus. An NTD is an abnormality in which the skull or spine has failed to develop normally.
Because it is a screening test, only about 5 percent of all mothers with elevated MSAFP values and only about 10 per cent of all mothers with low MSAFP values carry an abnormal fetus. Therefore, if your blood test is abnormal, it is still very, very likely that your fetus IS NORMAL.
The TT ("Triple Test")is similar to the MSAFP blood test, except that each measures two other substances in the blood of the mother -- beta hCG (human chorionic gonadotropin) and unconjugated estriol (also called E3, a form of estrogen). By determining the ratios of AFP to hCG to E3, the TT is believed to be more accurate in detecting the presence of chromosomal abnormalities. The TT is also known as the AFP-Plus blood test.
If either of these tests is abnormal, you may have an ultrasound examination to:
1. detect the presence of an NTD or ventral wall hernia
2. look for anatomic abnormalities associated with abnormal chromosomes
3. guide an amniocentesis
4. check for fetal viability
5. check to see how many fetuses are present
Provided that you are far enough along in your pregnancy, the ultrasound examination you have may be a complete Level II (explained below).
I chose to tell you about the LEVEL II ULTRASOUND EXAMINATION for several reasons:
1. I believe it is valuable
2. Many people have questions about it
3. Many people do not understand its purpose
First, a little history. The term "Level II" is somewhat of a misnomer in this day and age. Its origins are in the early days of ultrasound where a more detailed ultrasound examination was performed to explain the abnormal results of a screening blood test, called the MSAFP Blood Test (see above). To explain those results, a "Level II" study was performed. Physicians still use the term "Level II" because it is a convenient short-hand way of communicating among ourselves, even though the purpose of the Level II has changed.
Today, the Level II ultrasound, is an examination designed to look for anatomic abnormalities of the fetus. It is generally performed between 18 and 22 weeks menstrual age. There are six basic reasons for doing this:
1. To detect problems which may be incompatible with life outside the uterus.
2. To detect problems which may require the presence of specialized personnel in the delivery room.
3. In the event of an abnormality, to help parents-to-be prepare (e.g., contact support groups, etc).
4. If an abnormality is found, to allow parents the option of intervention, a follow-up ultrasound and/or genetic testing.
5. The maternal serum alpha-fetoprotein (MSAFP) blood test or "Triple Test" (TT) was abnormal.
6. To provide reassurance to the prospective parents that their fetus is all right.
What does the examiner look for while performing a Level II ultrasound? Interestingly, it depends. Guidelines for a Level II have been set by different organizations.
These organizations are:
Each organization's guidelines are different, although they are somewhat similar to each other.
In general, the examiner will look at the fetal brain
(echoencephalography), heart (echocardiography), stomach, kidneys, spine and umbilical
cord insertion site (the area of the navel or umbilicus or "belly button"). In
addition, the examiner will determine the position of the fetus, the
amount of amniotic fluid present (too much, too little or the correct amount) and the
location of the placenta. Some examiners do more than others, but most people do at least
the things I have mentioned. To see images
from a "Level II" ultrasound examination, click here. Using a 14.4 modem,
this will take about 120 seconds to load.
If an abnormality is found, your doctor may recommend genetic testing, e.g., an amniocentesis. This is because some anatomic problems are associated with genetic abnormalities.
Who should do the Level II ultrasound? This is a tough question. Firstly, I feel that all Level IIs should be interpreted by a physician experienced in interpreting Level IIs. There are many physicians who do not scan, but review and interpret the work of technologists. Secondly, the person performing the Level II should be experienced and specially trained in the performance of the study. Thirdly, the equipment used to perform the study should be adequate. Fourthly, if the person performing the Level II is the person interpreting the study, then you, the patient, can know the results by the end of the examination instead of waiting to find out. I think this is courteous.
In conclusion, my opinion is that a Level II ultrasound examination should be performed by an experienced individual (preferably a physician) using adequate equipment and interpreted by a physician with experience in doing this kind of work.
For your information, there are examinations which are performed that are designed to look in greater depth at single organs or organ systems (e.g., the skeleton, heart, brain, etc.) These studies are variously called, among other things, LEVEL III, TARGETED or DIRECTED ultrasound examinations.
HOW MANY ULTRASOUNDS DO I NEED?
"Need" is the key word. This will depend on several factors:
1. How healthy the pregnancy is. As you can imagine, the less healthy a pregnancy is, the more it may need to be followed by ultrasound.
2. How your physician was trained. Habits physicians develop affect how they practice medicine. If your physician is not accustomed to using the information ultrasounds provide, then he or she may order fewer studies. If your physician is accustomed to relying heavily on such information, then he or she may order more studies. It just depends.
3. How conclusive the prior ultrasound was. By this I mean that sometimes the results of the ultrasound are uncertain and questions remain. This can be absolutely normal and does not mean that anything is wrong. For example, it is possible to have an inconclusive study if the fetus is in a position where not all of its anatomy is visible. Those parts which cannot be seen cannot be evaluated. Therefore, you may need another examination to evaluate what could not be seen at the time of the earlier exam.
4. Was another test abnormal? If, for example, the Triple Test or MSAFP test was abnormal, your physician may request an ultrasound. Had the test been normal, the ultrasound may not have been requested.
There are other reasons affecting the number of ultrasounds your physician may request. But, you get the picture -- there is no way to predict how many you will "need."
Various diagnostic procedures may be performed during pregnancy to diagnose different conditions which may occur. Virtually all of these should be performed under continuous ultrasound guidance to prevent injury to the fetus. Among these procedures are:
performed to test the amniotic fluid for the presence of chromosomal abnormalities, NEURAL TUBE DEFECTs or VENTRAL WALL HERNIAs in the fetus. Later in pregnancy, it may be performed to assess fetal lung maturity prior to delivery. To perform an amniocentesis, the physician inserts a needle through the mother's abdomen into the gestational sac ("bag of waters") and withdraws some fluid. The fluid is then tested. When looking for chromosomal abnormalities, the cells in the fluid are evaluated. When looking for neural tube defects, ventral wall hernias or fetal lung maturity, chemicals in the fluid are evaluated.
Chorionic Villus Sampling ("CVS")
to test placental tissue for the presence of fetal chromosomal abnormalities. CVS is generally performed in either one of two ways. The first is similar to an amniocentesis. A needle is inserted through the mother's abdomen into the placenta, not into the gestational sac. Placental tissue is withdrawn through the needle. The second method is to place a plastic tube, known as a catheter, through the cervix into the placenta. Placental tissue is withdrawn through the catheter.
PUBS
a needle is placed into an umbilical vessel to test the blood of the fetus for the presence of abnormalities. To perform a PUBS, the physician inserts a needle through the mother's abdomen into the gestational sac ("bag of waters"), into the umbilical cord and withdraws some blood. The blood is then tested.
Fetal Skin Biopsy
a small amount of skin is removed from the fetus to test for certain abnormalities. To perform a fetal skin biopsy, the physician inserts a sampling device through the mother's abdomen into the gestational sac ("bag of waters") and removes some fetal skin. The sample is then tested.
Color Doppler imaging is used mainly to image blood vessels which are difficult to see using the gray-scale image only.
Using color Doppler technique, flowing blood appears as an area of color in an otherwise gray-scale image.
SPECTRAL DOPPLER
Spectral Doppler is used to obtain information regarding the qualities of the blood that is flowing in a vessel.
Copyright 1998-2008, Michael Applebaum, MD,
JD, FCLM. All rights reserved.
Suite 935 East, 845 North Michigan Avenue, Chicago, IL 60611- 2252, (312) 337-0732
Please send comments regarding this Web site to webmaster@drapplebaum.com
AC -- Abdominal Circumference. A measurement used to determine fetal age.
AFAFP -- Amniotic Fluid Alpha FetoProtein. Alpha fetoprotein found in the amniotic fluid. See AFP
AFP -- Alpha FetoProtein. A chemical found in the amniotic fluid and the mother's blood which is produced by the pregnancy.
AFP-Plus -- A blood test performed on the mother's blood to detect certain fetal abnormalities. It is usually performed between sixteen and nineteen weeks menstrual age. The same as the Triple Test.
AI -- Artificial Insemination
Amnio -- shorthand for an amniocentesis
Amniocentesis -- A testing procedure in which a needle is inserted into the amniotic sac ("bag of water") and fluid is withdrawn. The fluid, including the cells in it, is analyzed for chromosome and biochemical abnormalities.
Amnion -- One of the fetal membranes. It surrounds the fetus and is inside the chorion. By approximately 16 weeks, the amnion fuses to the chorion to form a unified double membrane, the "chorio-amniotic" membrane.
Applebaum's Rule -- A method of estimating the due date for people who have had AI, IUI, IVF, TET, ZIFT or GIFT
BPD -- Biparietal Diameter. A measurement used to determine fetal age.
Cervical Canal -- the birth canal.
Chorion -- One of the fetal membranes. It surrounds the fetus and is outside the amnion. By approximately 16 weeks, the amnion fuses to the chorion to form a unified double membrane, the "chorio-amniotic" membrane.
Chorionic Villus Sampling (CVS) -- A testing procedure in which a sample of tissue is removed from the placenta and analyzed for chromosome abnormalities.
cm -- Centimeters. There are 2.54 centimeters in an inch.
Color Doppler -- An ultrasound technique used to locate areas of motion, such as blood flowing within vessels.
Corpus Luteum -- literally, a "yellow body." What a dominant follicle evolves into after it ruptures. A normally functioning corpus luteum secretes progesterone in amounts adequate to support a pregnancy.
CRL -- Crown-Rump Length. A measurement used to determine embryonal or fetal age.
CVS -- see Chorionic Villus Sampling
Cyst -- A fluid-filled structure.
Doppler -- In ultrasound, a technique used to detect and evaluate moving structures. It is usually applied to the evaluation of blood flowing in vessels.
Embryo -- The developing human up to 10 weeks menstrual age
Endovaginal Ultrasound -- An ultrasound examination performed with an ultrasound transducer placed in the vagina. Same as transvaginal.
Fetus -- The developing human from 10 weeks menstrual age until delivery
FL -- Femur Length. A measurement of the length of the thigh bone used to determine fetal age.
Follicle -- A functional cyst within the ovary.
Gestation -- The pregnancy itself, also the period of time between conception and birth.
GIFT -- Gamete IntraFallopian Transfer
Internal Cervical Os -- the portion of the birth canal by the uterus.
IUI -- IntraUterine Insemination
IVF -- In Vitro Fertilization
lb -- pound, as in 16 ounces
Level II Ultrasound -- An ultrasound examination performed to evaluate the fetus for structural/anatomic abnormalities.
LMP or LNMP -- Last Menstrual Period or Last Normal Menstrual Period. A shorthand term for the date of the first day of normal menstrual bleeding prior to getting pregnant.
mm -- Millimeters. There are 10 millimeters in a centimeter. There are 25.4 millimeters in an inch.
MSAFP -- maternal serum alpha fetoprotein. Alpha fetoprotein found in the mother's blood. See AFP
MSAFP-PLUS -- A blood test performed on the mother's blood to detect certain fetal abnormalities. It is usually performed between sixteen and nineteen weeks menstrual age. The same as the Triple Test and AFP-Plus.
MSD -- Mean Sac Diameter. The size of the gestational sac ("bag of waters"). Usually measured during the first trimester.
Nagele's Rule -- A method of estimating the due date.
Neural Tube Defect -- see NTD, below
NTD -- neural tube defect. Any of a group of abnormalities related to the fetal brain and spine.
oz -- Ounce, as in 16 to a pound.
Percutaneous umbilical blood sampling -- see PUBS
Placenta -- The after-birth. Where nutrition goes from mother to the gestation.
Placenta Previa -- a placenta located in front of the internal cervical os, blocking the birth canal
Probe -- The ultrasound transducer. The instrument the person performing the ultrasound examination holds.
PUBS -- Percutaneous umbilical blood sampling. A test for fetal abnormalities in which blood is removed from the umbilical cord.
Scan -- The ultrasound examination.
Scanner -- The person performing the ultrasound examination.
Sonographer -- The technician performing the ultrasound examination.
Sonography -- Literally, writing with sound.
Sonologist -- The physician performing the ultrasound examination.
TET -- Tubal Embryo Transfer
Transabdominal -- An ultrasound examination performed with the transducer on the abdomen.
Transducer -- The ultrasound transducer. The instrument the person performing the ultrasound examination holds.
Transvaginal -- Same as "endovaginal."
Trophoblast -- embryonal tissue that contributes to the formation of the placenta.
TT -- Triple Test. A blood test performed on the mother's blood to detect certain fetal abnormalities. It is usually performed between sixteen and nineteen weeks menstrual age. The same as the AFP-Plus Test.
Ultrasound -- Sound beyond the range of human hearing.
Umbilicus -- the "belly button."
Ventral Wall Hernia -- a protrusion of the contents of the fetus, usually its abdominal organs, outside of its body.
Vitelline Duct -- Connects the yolk sac to the embryo/fetus.
Yolk Sac -- An embryonal structure upon which the early embryo is located. The earliest embryonal heartbeat is detectable adjacent to this structure.
ZIFT -- Zygote IntraFallopian Transfer
This baby diary includes worksheets for the ultrasound examinations and other tests you and your baby MAY have during the pregnancy.
REMEMBER: There is no standard or fixed number of ultrasounds you should of must have. Your doctor will determine that based upon his/her particular way of practicing medicine and your clinical condition.
GENERAL STUFF
Date of first day of LMP ____/____/_____
or
Date of AI, IUI, ET, GIFT, ZIFT, TET ____/____/____
Estimated date of delivery using either Nagele's or Applebaum's Rule ____/____/____
Physician's Name
Physician's Phone Number
Physician's Address
Names of Physician's Associates
Name of Hospital at Which You Will Deliver
Hospital Phone Number
Hospital Labor and Delivery Ward Phone Number
Hospital Address
Who to Call After You Deliver
Emergency Phone Numbers
FIRST TRIMESTER WORKSHEET
Institution Where the Ultrasound is Performed
Address of Institution
Phone Number of Institution
Date of Examination ____/____/____
Expected Embryonal/Fetal Age Based on LMP _____weeks
_____days
Expected Embryonal/Fetal Age Based on Date of AI, IUI, ET, GIFT, ZIFT, TET ____weeks
____days
Person Performing the Exam
Name of Physician Interpreting Exam
CRL _______mm
MSD _______mm
Heart Rate of Embryo/Fetus _______ beats per minute
Estimated Gestational Age by Ultrasound _____weeks _____days
SECOND TRIMESTER WORKSHEET
Institution Where the Ultrasound is Performed
Address of Institution
Phone Number of Institution
Date of Examination ____/____/____
Expected Embryonal/Fetal Age Based on LMP _____weeks
_____days
Expected Embryonal/Fetal Age Based on Date of AI, IUI, ET, GIFT, ZIFT, TET ____weeks
____days
Person Performing the Exam
Name of Physician Interpreting Exam
MSAFP/Triple Test or AFP Plus Result Normal Abnormal
"Level II" Results
BPD ____mm
FL ____mm
AC ____cm
Estimated Fetal Age by Ultrasound _____weeks _____days
Estimated Fetal Weight _____gm or _____oz
Fetal Heart Rate _____ beats per minute
Fetal Brain Normal Abnormal
Fetal Spine Normal Abnormal
Fetal Heart Normal Abnormal
Umbilical Cord Insertion Site Normal Abnormal
Fetal Kidneys Normal Abnormal
Placental Location
Cervical Length Normal Abnormal
Gender Male Female
Names Under Consideration
THE Name
Notes/Comments
Copyright 1998-2008, Michael
Applebaum, MD, JD, FCLM. All rights reserved.
Suite 935 East, 845 North Michigan Avenue, Chicago, IL 60611- 2252, (312) 337-0732
Please send comments regarding this Web site to webmaster@drapplebaum.com