Inside the Womb: Ever wondered what really happens in there?

By Heather Kempskie

In a single, nine-month sweep of time, a new human being, unlike any other ever born, emerges from a single cell. “Your Developing Baby: From Conception to Birth” will take you on a guided tour of the development of a baby in the womb. P&K asked authors Peter M. Doubilet, MD, PhD. and Carol B. Benson, MD, who are also professors of radiology at Harvard Medical School and teach and see patients at the Brigham and Women’s Hospital in Boston, to answer some commonly asked questions.

P&K: Some women have had several ultrasounds during their pregnancies others had only two. What is standard?

B&D: In the United States, unlike some European countries, there is no national standard for the number of ultrasounds during pregnancy. It is fairly common for healthy women with low-risk pregnancies to have two ultrasounds, one when they are between 11 and 14 weeks pregnant, and a second between 16 and 20 weeks. The first ultrasound is sometimes performed in conjunction with a blood test, to check for abnormalities such as Down syndrome. The second ultrasound is done to make sure the baby’s organs are developing normally. In some cases, a third ultrasound is performed later in pregnancy to make sure the baby is growing appropriately.
 

P&K: Most expectant parents can’t make heads or tails out of the grainy ultrasound images. Can you provide a quick 101 on deciphering an image?

B&D: The main types of ultrasound are two-dimensional (2D) and three-dimensional (3D). The 2D images are especially difficult for parents-to-be to understand at first, because these images show “slices” of the baby’s body (like slicing a loaf of bread to see the inside). These 2D pictures show the organs inside the baby’s body, structures that may not be familiar to parents. Parents should ask the person performing their ultrasound to point out some of the baby’s structures while the scan is going on.

 

P&K: During an ultrasound, we’re busy looking at the image of the baby and are only faintly aware of what the technician is doing. What is she doing?

B&D: Very early in pregnancy, ultrasound is used to determine if the pregnancy has one baby or twins or triplets, and to check the size and heartbeat of each baby. During scans in the second and third trimester, there is a lot more to look at. Pictures of the baby’s organs, such as the heart, brain and kidneys, are taken to make sure they are developing normally. The baby is measured to confirm that he or she is growing normally. In addition, pictures are taken of the baby’s “support structures,” including the placenta, umbilical cord, and amniotic fluid.

P&K: The person performing the ultrasound holds the key to sharing the sex of the unborn baby. Are you finding that more parents want to know these days?

B&D: The sex of the baby can usually be determined on ultrasound by about 16 weeks of pregnancy. In our experience, about 80-85 percent of parents want to know the sex of their baby. Over the 20 or more years that we have been doing ultrasound, this percentage has not changed.