Prenatal Ultrasound

09.23.10: To peek or not to peek?


Emily wonders if all the ultrasounds her doctor recommends are really necessary. She’s healthy and wants to avoid interventions. She didn’t have a 6-week ultrasound and is weighing her options on the upcoming 18- 20-week one. Her question is can doctors really do anything about it if they find something wrong?

Emily, I understand your concerns. Women delivered without ultrasounds for thousands of years and now, it seems some practitioners hand them out like Pez.

On the other hand, when used properly, ultrasounds can provide important information that might make a big difference to your or your baby’s health. For example, they can tell if there’s one baby or two or if the placenta is blocking the cervix. They can tell if a baby has Spina bifida, extra limbs, is missing a kidney or other pieces of anatomically useful information. When a problem is suspected on a standard ultrasound, a more specialized ultrasound will be prescribed.

Ultrasound is also used to guide screening and diagnostic tests like amniocentesis. In late pregnancy, when there’s concern about babies who aren’t moving a lot or who look “funky” on fetal heart monitoring, ultrasounds can provide real reassurance through a test called a biophysical profile that might actually prevent further interventions. And yes, they can sometimes help solve problems (like certain heart defects) before they become a crisis.

One of the biggest uses for ultrasound is to determine fetal age and a due date. The most accurate time for that is in the first trimester. Emily, if you have any question about when your last period was or when you might be due get your ultrasound sooner than later. Ultrasounds are far less accurate for that purpose in the second trimester and even less in the third. In fact, second and third trimester ultrasounds can miscalculate a due date by plus or minus two weeks. That’s particularly important if a doctor/midwife thinks you’re over due, schedules an induction and then… oops; discovers your cervix won’t dilate or worse, delivers a premature baby because you weren’t actually due for a couple weeks.

Everybody should be taking a closer look at pesky ultrasound limitations in light of ever-increasing induction, c-section and maternal and newborn mortality rates. Ultrasounds can be waaaay off in predicting how big a baby is too. I’ve had patients be induced and even c-sectioned because their ultrasound and doctor said their baby was getting too big. Then, they deliver a normal-sized baby who would have had no trouble fitting through the birth canal and didn’t need to be delivered early after all.

Ultrasounds can be very useful but they aren’t perfect. Here’s what the March of Dimes says:

“In low-risk women, ultrasound is good at ruling out problems but not as good at detecting them. Studies suggest that a routine ultrasound exam detects about 40 percent (with a range of 13 to 82 percent) of all structural birth defects. Ultrasound appears most accurate when done by an experienced examiner, generally at a major medical center.

Besides missing some birth defects, a routine ultrasound exam can occasionally suggest that a birth defect is present when none exists. While follow-up exams often show that the baby is healthy, such false alarms can cause intense worry for parents.”

Why Emily might want an ultrasound:

• If you’re one of the women who need it, say, you’re carrying twins or a have a funky placenta; ultrasound could save you from serious trouble.

• If you don’t know when you had your last period or when you got pregnant, ultrasound can help determine a due date.

• If you’ve had trouble with a previous pregnancy or there’s something “iffy” about your current one, finding out everything’s OK (or not) could be priceless.

Why Emily might not want ultrasounds:

• She wants her baby to develop in privacy, without medical intrusion.

• She doesn’t want doctors/midwives stirring up trouble that doesn’t really exist, just to say later, “Whew, everything’s OK after all.” Most babies are born healthy when mothers are healthy.

• She has no medical reason for getting one.

Ultrasound has been studied and widely used for over 40 years and so far, so good. We know that professionally done, for brief periods of time, ultrasounds don’t appear to cause any problems. That doesn’t mean you should rent your own machine and produce your own “baby channel.”

The key to safety is: limited use by professionals only, when there’s a reason to do one. Ultrasound uses a type of energy (sound waves) to produce images. There’s some concern that overuse could raise body temperature. Does this cause fetal damage? We haven’t seen it so far, but we don’t want to experiment by bouncing babies with too much ultrasound. Leave this job to the professionals who know how to get the info they need and get the heck out quickly.

Emily, if you’re not comfortable with ultrasound and your health practitioner doesn’t provide any reason to do one, it’s OK to say “no.” And to the women out there who have no medical reason to get one other than to just to take a peek, determine whether it’s a boy or girl or to get a keepsake photo; it’s OK for your insurance company to say “no” too.

Jeanne Faulkner, R.N., lives in Portland, Oregon with her husband and five children. Got a question for Jeanne? E-mail it to and it may be answered in a future blog post.

This Fit Pregnancy blog is intended for educational purposes only. It is not intended to replace medical advice from your physician. Before initiating any exercise program, diet or treatment provided by Fit Pregnancy, you should seek medical advice from your primary caregiver.