Ultrasound Images of Your Growing Baby Boy

What to Look For

Person holding an ultrasound image over a baby boy

 Cavan Images / Getty Images

For most expectant parents, finding out the sex of their fetus on ultrasound is more of a curiosity than a necessity. But for some people, learning the sex of their fetus is very important, especially if they are considering invasive testing for a male sex-linked disorder like Duchenne muscular dystrophy or hemophilia.

During your pregnancy, you will likely have at least one or two routine ultrasounds. You may have more if your doctor thinks they are indicated. Except in certain circumstances, prenatal ultrasounds are not done specifically just to check on the fetal sex.

Remember, a healthy baby is your ultimate goal and the real reason for prenatal ultrasound is to help make sure you achieve that goal. Here is what that ultrasound may look like at different stages when you're carrying a boy.

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Your Baby's Ultrasound: What to Expect

Early Ultrasound

Having an ultrasound between 11 to 14 weeks is common. An ultrasound at this gestational age will help confirm your due date, and it is part of the early risk assessment testing (ERA) for a chromosomal abnormality, such as Down syndrome.

The ultrasound technician will measure the fold on the back of the fetal neck. Both a boy and a girl fetus have this fluid-filled space. If the thickness of the nuchal translucency is more than 3.5 mm, it is associated with an increased risk of Down syndrome.

At this gestational age, you can't distinguish between the genders on ultrasound. The part of the fetus that is developing into either girl parts or boy parts is called the genital tubercle. The way the genital tubercle forms into the penis of a boy fetus is different from how it forms into the clitoris of a girl fetus.

11 to 14 Week Ultrasound

By looking at the angle of the genital tubercle, it is possible to distinguish between a boy and a girl fetus. But remember, this is usually not part of the routine ultrasound at this gestation age.

The ultrasound technician needs to look at certain additional views of the developing fetus in order to determine this angle. Not all technicians feel comfortable with making these measurements and confirming a boy fetus.

What Needs to Happen to Make a Boy

A lot has happened by the time your boy fetus reaches 16 weeks. Even before the genital tubercle develops into boy parts, changes occur to set up the development of these recognizable boy parts—namely the penis, scrotum, and testicles.

The first step in becoming a boy starts with the fertilization of an egg with a sperm containing a Y chromosome. The SRY gene or the sex-determining region on the Y chromosome determines that testicles will develop.

By six weeks, the early testicle cells release a substance that prevents female genital development. By nine weeks, testosterone is produced. Testosterone is the major sex hormone in men and it is necessary for the continued fetal development of a boy's sex organs.

By 14 to 16 weeks, under the influence of testosterone, the genitals of a boy fetus begin to be recognizable.

Dating Ultrasound

It is not routine to have an ultrasound at 16 weeks, however, sometimes you are late to prenatal care or your dates may be off and you end up being farther along than you thought. In these situations, you may actually be sixteen weeks (or more) at the time of your first ultrasound.

At this point, it is too late to do the early risk assessment testing. But the technician will take measurements of your fetus that will help establish or confirm your due date.

By 16 weeks, all of the parts of your boy fetus are formed. Now fetal development is focused on growth.

Preterm Labor Risk Assessment

Another reason you may have an ultrasound at 16 weeks is to check the length of your cervix. This is typically done if you delivered a preterm baby (before 37 weeks) in a prior pregnancy. Unlike the typical prenatal ultrasound, this is a transvaginal ultrasound and is done only to measure your cervix.

Although not well understood, research suggests that a male fetus is associated with an increased risk of preterm labor. So, if you have a history of preterm delivery and you are pregnant with a boy baby, be sure to discuss cervical length checks with your doctor.

By 16 weeks, you can start to see a more well-defined penis and scrotum on ultrasound.

18- to 20-Week Ultrasound

It is recommended that you have an ultrasound between 18 to 20 weeks. The purpose of this ultrasound is to be sure that your fetus is developing normally. This ultrasound is often called an anatomy scan.

It is possible you may be scheduled for a more comprehensive and detailed ultrasound. This special ultrasound is called a level 2 ultrasound and may be recommended if:

  • You are carrying twins.
  • You are older than 35 years.
  • You have a family history of congenital malformations.
  • You have diabetes.
  • You were exposed to certain medications early in pregnancy.

And yes, this is the time that ultrasound can more reliably confirm that you are having a boy (if he cooperates).

Anatomy Ultrasound

The anatomy scan is about much more than finding a penis.

The ultrasonographer will look systematically at your fetus to be sure that all is developing normally. This is the time when congenital malformations are detected. Some congenital malformations found on routine ultrasound include:

  • Cleft lip/palate
  • Club foot
  • Congenital heart defects

The anatomy scan can also detect non-specific structural changes that can be associated with Down syndrome, especially if more than one of these findings are noted on the anatomy scan. Common soft markers of Down syndrome include:

Camera Shy?

Besides hearing that your fetus is developing normally, learning the sex of your fetus is arguably the most anticipated part of the anatomy scan.

By 18 weeks, the penis and scrotum are well developed and usually easily identified. The one obstacle to seeing if you are having a boy is the position of the fetus in your uterus. Sometimes the ultrasonographer is not able to get a good enough shot of the penis and scrotum to definitively say, "It's a boy!"

21 Week Ultrasound

Having an ultrasound at 21 weeks is not part of routine prenatal care. However, there are certain instances where you may find yourself having an ultrasound at this gestational age.

For instance, sometimes the position of the fetus inside the uterus makes it challenging to take the right photos. If the sonographer can't see everything they need to, you may be called back for a follow-up visit.

People who are at higher risk for preterm birth may also need a follow-up scan to check the length of their cervix. The risk of preterm birth increases as the length of the cervix decreases. In this case, a follow-up scan is used to see if there has been any change.

If you are having this unscheduled check, it does give you a chance to peek at those boy parts again. And if you are lucky, they are obvious enough to catch in a profile shot.

Monitoring a Complicated Pregnancy

Any ultrasound done after a detailed anatomy scan is performed is not part of routine prenatal care. Usually, it means there is something complicating your pregnancy that needs to be followed.

Maybe you have diabetes or high blood pressure, or maybe something was noted on your anatomy scan that needs to be reevaluated. The top three reasons that you may need ultrasounds during your third trimester include:

Managing your way through a complicated pregnancy with all of the extra testing and appointments can be stressful. But hopefully getting another look at your baby boy will brighten your day.

Descent of the Testes

The descent of the testes into the scrotum is a very important part of the normal development of your boy fetus.

It is a complicated process that begins when your boy fetus is only 10 weeks old. Between 10 to 15 weeks, the testes begin to move out of the fetal abdomen and into the area where the boy sex organs are forming. They stay in the fetal pelvis until about 26 to 35 weeks. Then, under the influence of testosterone, the testes begin to move down into the fetal scrotum.

By 32 weeks, both testes have descended in over 95% of boy fetuses.

Testicular descent is absolutely dependent on proper testosterone production by a male fetus. If testosterone production is inadequate or disturbed in any way, a condition called cryptorchidism can result.

About 3.4% of newborn boys delivered at term will have cryptorchidism. However, there is significant evidence that this anomaly is on the rise thanks to in utero exposure to endocrine-disrupting chemicals.

Antenatal Testing

Again, although not part of routine prenatal care, having an ultrasound in the few weeks before your due date is not uncommon. An ultrasound ordered at this point in pregnancy is often part of the biophysical profile—a specific test used to check for fetal wellbeing.

It is very likely that you will get a glimpse of what are now very obvious boy parts during this type of ultrasound. This image clearly shows a penis and scrotum, no interpretation necessary.

A Word From Verywell

Ultrasound photos are an exciting part of the pregnancy journey, but with an uncomplicated pregnancy, you may only get a glimpse or two. Still, it's helpful to understand the process of your baby boy's development so you know what to expect from the photos or just when visualizing the general stages of his growth.

Remember: Getting extra testing because you have a high-risk pregnancy is to help ensure that your 9-month journey goes well. While this can undoubtedly be stressful, these bonus sneak peeks at your baby boy on ultrasound can be a reminder (although probably an unnecessary one) of why these checks are all worthwhile.

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Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Andrea Chisholm, MD
Andrea Chisholm, MD, is a board-certified obstetrician and gynecologist with more than 20 years of clinical experience. She has taught at both Tufts University School of Medicine and Harvard Medical School, and she is currently on the Clinical Advisory Board of the International Association of Premenstrual Disorders.