Can ultrasound be wrong when saying boy or girl?

It’s a big decision whether or not to find out whether or not you are having a boy or girl at your ultrasound visit. If you have decided yes, it’s a big deal in the ultrasound room, waiting for the sonographer to break the big news. Once it is revealed, most people get excited but then they wonder if there is room for error. Even if it looks pretty convincing during your scan, afterwards chances are your friends and relatives will have stories to cast doubt on whether or not what you’ve been told is actually right.

So, if you’ve been told boy versus girl, can you bank on it? The answer is a somewhat unsatisfactory “Yes, MOST of the time…”

Why the ultrasound might be wrong:

  • Experience of the sonographer- You hope that whoever is doing your ultrasound is well trained with hundreds, if not thousands, of hours of supervised experience. Ultrasound is not as easy as it might look, and it can be easy to be fooled regarding gender if you are not properly trained. Girls have surprisingly prominent yet normal genitalia, which can sometimes be easily confused as ‘boy bits’ by someone without experience. Umbilical cord can also play tricks on a newbie, making a girl look like a boy.
  • Too early to call: One of the most common reasons for error is making the gender call too early. I have seen many cases where even the most experienced and respected high risk perinatologists have been wrong (and I must admit I have similarly misled families on a couple of occasions)  because we predicted gender at the 12 week nuchal translucency scan, only to discover the error at the 20 week anatomy scan (click for more info on what happens at these scans). A complete discussion on what fetal gender looks like at 12 weeks, including images, can be found in the post “Am I having a boy or a girl?” . The essential truth is that boys and girls look VERY VERY similar and BOTH have an external phallus at this point in development. Despite what boys and girls “should” look like at this scan, not all of them are blatant or clearly defined and predictions made at this early scan ALWAYS have some wiggle room for a mistake. Predictions at the 18-20 week scan are much, MUCH more reliable. In fact, as long as you have an experienced sonographer, you can count on what they tell you to be true more than 99% of the time.  Why only 99+% and not 100%?? Because some fetuses can have ambiguous fetal genitalia…
  • Ambiguous fetal genitalia: While not common, it is not completely unusual for fetuses to have abnormalities of the genitourinary tract, especially in boys, which can make an accurate determination of their gender difficult even after birth. There are also multiple cases reported where, in perfectly normal girls,  there is a temporary hypertrophy or enlargement of the clitoris and/or labia (which may or may not be related to hormonal imbalances), but which do regress to normal appearances before birth or in the first year of life.  In these cases, it is possible that a girl fetus could be mistaken for a boy. Additionally, there are some rare fetal chromosomal abnormalities and androgenital syndromes which can cause confusion regarding boy versus girl genitalia.

Fortunately, in the vast majority of cases, as long as you get your prediction at 18 weeks or more, your baby is almost certainly what you have been told. If you happen to have multiple scans as your pregnancy progresses, you should be able to throw out any lingering doubt that you may have. The good news is that in this day and age, if you want to know what you are having, you can do so with a high level of confidence.




20 Week Ultrasound



For many couples, the 20 week ultrasound (also known as anatomy scan) can be one of the highlights of a pregnancy. It’s a wonderful opportunity to see the actual form and movements of that growing person  that is driving all those big changes in your body. Finding out the sex CAN be done at this time, however, learning the gender of your baby is completely optional. If you don’t want to know, just inform the person doing your scan. Plenty of people don’t want to find out, and it is strict policy in all facilities not to carelessly divulge the gender. Nor are they permitted to give the gender information to anyone but the mother without her express consent. Click for more information about learning the sex of your baby.

Why the 20 week ultrasound is important:

The 20 week ultrasound can be done anywhere from 19-22 weeks, with the main purpose of the scan being to evaluate the baby’s anatomy. Many families are surprised at how much can be seen at this scan. Ultrasound is able to see the anatomy that lies within your baby including the brain, stomach, heart, kidneys, bladder, just to name a few. For detailed information on exactly what is investigated at your 20 week ultrasound, click the link. Because each bit of the baby’s body is carefully examined from the skull, brain, and down to the feet, this scan can take quite a while. Depending on whether or not the baby is in a cooperative position (similar to posing for pics at the portrait studio), the exam can take anywhere from 30 minutes to an hour.

Do I need a full bladder?

Some places will ask you to come in for your scan with a full bladder. Many don’t bother, but IF you are asked, then do make an effort to comply. In truth, your bladder does not need to be excruciatingly full so use some common sense when following the instructions. It’s not the AMOUNT of fluid you drink that is key (and just so you know, the examiner cannot tell the difference if you drank  10 oz. or 32 oz.; as long as you have feel like you could go, you should be OK). The point of asking you to drink is that a moderately full bladder can sometimes aid in getting a better view. So, drink a bit of extra fluids and don’t go  to the bathroom for about an hour before your appointment, and you should be plenty full. You don’t need to be so full that you are miserable! If you find you just can’t hold it, go (you don’t need to confess to the staff) but count to five slowly, then try to stop. You’ll be surprised to find that if you try, most people CAN stop (albeit not immediately) while still keeping enough in your bladder to keep your examiner happy.

Can I bring family to see the ultrasound?

Generally, husbands/partners are always welcome in the ultrasound room, just as they are in the labor suites. Most places that perform anatomy scans are very used to the occasional requests for additional ‘spectators’ such as grandparents, aunts, etc.  You are advised to check the policy of the facility performing your scan as whether they will allow multiple people in the exam room can vary from site to site. Often, they won’t mind, but it is a good idea to give a call to the office before you all show up together. Some places are more than happy to accommodate, some will only allow additional family in the room for a ‘tour’ of the baby after the medical part of the scan is finished, while others have policies against anyone other than parents.

For more information on how to read and understand what you are seeing at your ultrasound, click the link. This should help you and your ‘audience’ get the most out of what you are going to be seeing.

What about siblings?

Many parents want to bring their other child or children to see the ‘new’ baby’s ultrasound with them. Again, it is very important to check with the facility performing your scan as to whether minors are allowed in the exam rooms. Some places have very strict policies and issues with liability. Many places are going to discourage it, but if you do bring your other children with you, it is important that you have an adult (Dad, friend, or grandparent) there who can take the child (or children) out of the room if they get bored- which most eventually do. The anatomy scan can take a long time, and many times younger children simply do not have the attention span required to sit quietly in a dark room watching a black-and-white image of a ‘baby’ (not usually recognizable to them) for as long as needed.




Tips on understanding your baby’s 20 week ultrasound

At 20 weeks, the baby is completely formed and just needs to grow and mature. Even if you’ve never seen an ultrasound before, you should be able to recognize the shape of the baby and see it’s heart beating. Despite all the buzz about color 3D images of the baby, where it looks like a ‘real’ baby with the skin on, your ultrasound will mostly be the traditional black and white pictures you may have seen over the last couple of decades. This is because 2D is still the best way for the doctor and sonographer to see the structures below the baby’s skin, looking  inside the baby where the anatomy lives. Learn more about the differences of 2D versus 3D and 4D Below is a video of a 20 week 2D ultrasound.

To better understand what you are seeing, note that the very top of the image is the mother’s skin (where the probe is) and the bottom of the image is the mother’s muscles and spine behind the uterus. Think of the image as a top-down slice taken from the top (mother’s skin), through the uterus, through the placenta, fluid, and baby, with the bottom of the image being at the mother’s back. Parents quickly realize they are easily able to see right through the baby to the bones, ribs, etc., and many of them ask if the baby has skin yet or remark that the baby must still be transparent. The baby DOES have skin and is not transparent (think of a premature baby—it definitely is not transparent- slightly translucent skin maybe, but you certainly can’t see the bones and organs underneath).  The ultrasound beam is able to “see” through the fetus, just as it ‘sees’ through the mother’s skin to the structures  behind.

It will also help you to understand what the various shades of white/gray/black represent. On ultrasound, fluid is BLACK. You can see that the baby is moving surrounded by fluid (amniotic fluid) and there are areas of black within the baby as well, which are other types of fluid.  Cerebrospinal fluid (which you can see in the head) and blood in the heart and blood vessels  show up as black on ultrasound. On ultrasound, any WHITE  you see is bone and cartilage. The different shades of gray represent different densities of soft tissue such as the placenta, and muscles and organs within the baby. In the video above, you can see that there is a large patch of smooth gray above the baby and black of the amniotic fluid. This is the placenta, which lies just below the surface of the mother’s skin. This is known as an anterior placenta, which is a great location, however, it may affect how well the mother is able to feel the baby. Click for more on feeling fetal movements.

In the video above, notice how you don’t clearly see the arms and legs when you are able to see the beautiful profile of the face. This is because the ultrasound beam is being transmitted in a single plane, or a thin slice going from the top down. Since the slice is going straight along the fetal forehead, nose, lips, neck, and chest, the arms and legs are lying to the right and left side of the slice and aren’t visible. However, as you watch the baby move, you can see parts of the arms and legs coming in and out of the picture as the baby moves.

Is the baby’s gender going to be obvious? Again, because ultrasound is a single plane of data, you’re not able to see the whole baby ‘naked’ like you would if it were lying in front of you. In order to see the gender, specific views need to be taken between the legs, and good sonographers can usually avoid letting you see that view if you don’t want to know. Many people are confused by what  they are seeing even when they are shown that specific view between the legs, so don’t assume you’ll easily figure out what it is. Click for more on how to determine gender with ultrasound.

What does 3D or 4D look like at 20 weeks?

First of all, 4D is simply a series of single 3D images so that there is the appearance of motion. The 4th ‘D’ is time. Because 20 week fetuses are still skinny without much body fat, and their heads appear large compared to their thin limbs and body, they can look pretty scary. It is very hard to get a really cute 4D video at 20 weeks. The other important thing to remember when you look at any 3D/4D image is that it is a computer-constructed image, not a glimpse at the real thing. As such, the computer can make some odd assumptions as it is trying to render a pleasuring surface to the baby and weird bulges and lumps appear. In addition, the  image is being ‘directed’ by the sonographer, who uses the 3D/4D software to try and adjust the area in focus, rotate, expand, or contract the field of view to create the most pleasing image. Meanwhile, the baby is moving and wiggling, making the job of getting a good window of view even harder.

Below is a 20 week 4D video, and you can see how the sonographer is trying to chase the baby, rotate the picture to catch the baby at a pleasing angle, and cut away data (the placenta, cord, and hands) that is blocking view of the baby. Sometimes you’ll notice parts of the skull get cut out which makes it look as though there is a gaping hole in the head, the nose sometimes looks funny, the baby’s mouth is opening at times giving it an odd appearance, and is generally is not a video you’d want to show off to the family at holidays.  This video is unfortunately  pretty typical of the type of images we get on 20 week fetuses. Read more on the limitations of 3D and 4D.

Soft Markers

questions about pregnancy screening tests

Many parents look forward to their 18-20 week anatomy ultrasound (click for more information on the anatomy scan), only to discover that the doctor sees a ‘soft marker’. Soft markers are not abnormalities within the baby but are normal anatomical variants. In the quest to find fetuses that have Down’s Syndrome or other serious abnormalities, anything that was seen to be out of the ordinary has been greatly studied to see if there is a possible correlation between the variant and abnormal outcomes. Sure enough, there have been associations, albeit weak, between ‘soft markers’ and babies with Down’s or other problems. But before you panic, understand that even if you are told your baby has a soft marker, the chances are more than excellent that everything is fine. In fact, 10-15% of all babies have at least one soft marker. Most of the time, the finding of a soft marker in an otherwise normal-appearing baby is a big to-do about nothing. Years ago, doctors were more interested and wary when soft markers were found, but over time, it became clear that the most common problem associated with soft markers is unnecessarily scaring the wits out of parents. Much less emphasis is placed on soft markers now that we have more trusted, reliable screening methods such as First Trimester Screening and NT Ultrasound (click for more information).

The bottom line is that generally, in an otherwise low risk pregnancy with a normal first trimester screening test, the presence of a soft marker or two does not significantly increase the odds that your baby has a problem and more invasive testing with amniocentesis is not usually warranted. If you are already high risk such as being over 35 or the baby has other anatomical abnormalities, your doctor or a midwife will advise you as to whether or not amniocentesis is an appropriate next step.

What are soft markers?

Again, soft markers are not abnormalities but are anatomical variants. For example, an anatomical ‘variant’ is having naturally red hair—most people aren’t born redheads, but having red hair does not mean you are physically abnormal. It’s just the way you are built. Same goes for ‘soft markers’, most fetuses don’t have them, but if they do, most of the time they are not physically significant. But, in rare cases, they can be a clue that a larger problem exists.

The following is a list of some Soft markers:

  • Choroid plexus cysts: These are rounded cystic structures seen in the part of the brain that makes the cerebral-spinal fluid. Cysts in the brain sound scary, but they have no significance to the development and intelligence of your baby. They are significant in that 30% of babies with Trisomy 18 have them, but keep in mind, very few babies with choroid plexus cysts have Trisomy 18!
  • Borderline ventriculomegaly: In the brain, the lateral ventricle is a structure which holds some of the cerebrospinal fluid. It is routinely measured on every anatomy scan to look for hydrocephalus or ‘water-on-the-brain”. If it is prominent, meaning it is at the very upper range of normal, it can be associated with a host of problems. It is more common and more likely to be normal in boys than girls. If this is found, your doctor will likely do some additional testing and follow ups just to make sure it doesn’t represent a problem or worsen.
  • Echogenic intracardiac focus: Fancy words for a ‘bright spot’ in the heart which represents some calcifications or prominence to the papillary muscle. This doesn’t affect the function of the muscle or the beating of the heart. It’s seen in approximately 20% of all Down’s Syndrome fetuses. This is a relatively common finding on ultrasound, approximately 5% of all fetuses have this. Yet only approximately .25% of fetuses have Down’s Syndrome. Incidentally, it is more commonly found in Asian mothers than others, and is much more likely to be normal than indicative of Down’s.
  • Echogenic Bowel: Sometimes there can be very bright spots seen within the baby’s abdomen or liver. Most of the time, this represents nothing but in some cases, it can be caused by Down’s Syndrome, cytomegalovirus (CMV), or cystic fibrosis. A few normal babies with echogenic bowel will show poor growth later in the pregnancy so your doctor might order follow up ultrasounds in the later 2nd and 3rd trimesters to follow growth.
  • Single umbilical artery: Most babies are born with an umbilical cord that contains 2 arteries and one vein. Normal cords are known as 3 vessel cords. Sometimes, there is only one artery and one vein. Again, most of the time, this is just a curiosity and the baby is born healthy and well. However, in some cases, 2 vessel cords can be associated with kidney or heart abnormalities and/or poor growth. A careful look at the anatomy will be performed to rule out any associated defects.  Additional ultrasounds will likely be done to follow the growth.
  • Mild pyelectasis: This occurs when there is fluid within the part of the kidney that collects urine. A little bit of fluid (less than 4 mm.) is perfectly normal. More than that has been loosely correlated with Down’s Syndrome. Even if Down’s Syndrome is not suspected, chances are you will have follow up ultrasounds to keep track of the amount of fluid. In some cases, the amount of the fluid can increase and signal a urinary blockage or other problem with the kidney and bladder. Again, these follow ups can be nerve-wracking but most of the time, even if the kidneys continue to retain fluid, it can be medically managed and successfully treated after the baby is born.

Should you find yourself in the position of being told your baby has any of these issues, try not to assume the worst. Your doctor or midwife is obliged to tell you of the findings and the risks, which can sometimes sound horrible. How alarmed you get is often a function of the personality of your doctor or midwife. Some will emphasize all the worst case scenarios since there are no guarantees in medicine (OR parenting, for that matter). Despite being told that something might be wrong, believe them if they say they your risks are low and they are not concerned.



The Anatomy Scan: 18-20 week ultrasound

20 week 3D image

At around 5 months from your LMP (last menstrual period),
your doctor or midwife will send you for an ultrasound. At this scan, you can
find out the sex IF you choose. Keep in mind that there are some areas and some
countries where it is policy not to reveal gender, but generally, this is the
scan where the sex can be reliably determined. Click for more about how we see boy versus girl Many people look most forward to this scan because of the possibility of finding out the gender, but there are so many more important reasons to do this scan. All of the baby’s anatomy from head to toe will be carefully examined, and lots of measurements are taken to ensure normal growth. In order to see the anatomy that lies beneath the surface of the skin inside of your baby’s body, the images will be taken in black and white 2D (rather than those fancy 3D images).

Click for tips on how to read and understand your 20 week ultrasound.


This scan is very important since it has been repeatedly demonstrated in multiple studies across different countries that performing an anatomy scan makes a difference in overall rates of infant mortality. Identifying fetuses with an anatomical abnormality before birth allows for delivery of the infant in the proper hospital environment with a prepared team of doctors and professionals who can give your baby the best possible care. For example, if you live in a remote area, knowing that your baby has a serious physical abnormality before it is born means you can plan to give birth in a hospital that has specialized neonatal care unit with experts who are equipped and prepared to handle your baby’s special needs.

20 week 3D image

20 week 3D image

Because there is so much to examine, this scan can take quite a while. In addition, sometimes the  baby simple doesn’t cooperate and insists on lying in a position that makes visualization of some structures impossible. There is no bad position for the baby at this point, but there are bad positions for getting good photos!! Occasionally, you may need to come back later in the day or at another appointment to get a complete exam.

What things do the doctors check on this ultrasound?

  • The fetal brain structures are thoroughly examined to ensure that they appear normal and there are no blockages or
  • The fetal face, eyes,  lips, skull, and jaws are imaged, ensuring that everything appears normal and there is no cleft lip.
  • Internal organs such as the kidneys, diaphragm, stomach, bladder, thorax, and intestines are examined. Blockages or defects in
    these areas can be identified and, in some cases, some interventions can be performed if blockages are seen. For example, if kidney or bladder blockages are seen, doctors can place a thin drainage tube which can prevent damage to the organs
    until proper surgical repair can be done after birth.
  • The spine is examined to make sure the skin is closed and there is no evidence of spina bifida (an opening in the spine) or
    other problems.
  • The arms, legs, hands, and feet will be examined. It is hard to account for each individual finger and toe, but the
    general structure of the hands and feet is checked.
  • The umbilical cord will be checked to ensure that it enters the abdomen normally and that it has 3 vessels. The umbilical cord
    should have 2 arteries and 1 vein. Sometimes only 1 artery and 1 vein is seen (known as a 2 vessel cord). This is not a terrible thing but follow up ultrasounds will be needed to ensure that the baby is growing well.
  • The baby’s arm and leg bones, head, abdomen, and bones are measured which allows an assessment of the overall growth of the baby.
  • Fetal heart: many images of the heart and the main vessels are examined. These images can sometimes take a while since the
    heart is a moving structure and getting a thorough exam can often be difficult. If the baby’s position prevents a good evaluation or a possible abnormality is suspected, you may be referred for a fetal echocardiogram. Fetal echocardiography is an exam performed  by a doctor who specializes in prenatal and infant hearts. He or she can best evaluate and address any potential problems that might be found. Rest assured, most of the time, the exam turns out to be normal.

In addition to looking carefully at the baby, the uterus, amniotic fluid, and cervix will be checked. The cervix should appear long and
closed. If it is doesn’t appear as expected, this can alert your doctor to the possibility that you are at higher risk for pre-term labor. Follow up examinations may be required and, if it is decided that the cervix is indeed  beginning to dilate and open, a procedure known as a cerclage (click for more info) can be performed where the doctor inserts a stitch to hold the cervix closed.

The placenta will also be examined and the location documented. The only time the placental location is a concern is if it lies at
the cervix. If it is completely covering the cervix, it is known as a placenta previa. If the edge of the placenta is at or near the cervix, this is known as a low-lying placenta. For more information, click here.

Because the placenta is a vascular structure that is embedded in the uterine wall by a multitude of blood vessels, if it lies at the cervix and the cervix begins to dilate, it can cause a severe life-threatening emergency for mother and baby. Fortunately, true previas are uncommon and occur in only about 5% of pregnancies. However, it is not uncommon at this 18-20 week scan to be told
that the placenta is low-lying and needs to be followed up with another ultrasound at a later date. Try not to worry since most of the time, a low-lying placenta will migrate away from the cervix as the uterus expands and will not be a concern by the third trimester.

Hopefully, the baby will be in a good position and you will get some good photos for you to take home with you. If the baby is cooperating and your ultrasound center has the capabilities, you may get some 3D/4D pictures as well. However, babies are skinny at this time in development and often, the 2D profiles are the cutest. Click for more on the limitations of 3D/4D and to view a 20week 4D video.

Below is a video of a 2D 20 week fetus in a beautiful, face-up position. Here you can see it flexing and moving, and the heart can be seen as the area of fluttering motion in the chest.

Click for more tips on understanding your ultrasound.


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