Should You Worry About the Size of Your Bump—and Your Baby?

Our maternity nurse weighs in on what it means if your baby is measuring small during ultrasounds.

Pregnant Women Holding Ultrasound Image
Photo: Natalia Deriabina/Shutterstock

I get questions all the time based on dumb stuff friends and family say that freak pregnant women out. C'mon guys, leave these poor mothers alone. If she's getting good prenatal care, let her doctor be the one to voice concerns.

One mom-to-be was worried that her bump—and her baby were measuring small at 33 weeks. At 3 pounds at that point, the baby is certainly measuring smaller than average. We'd expect her little one to be closer to 4 pounds at this point.

However, a single ultrasound doesn't always indicate accurate size and growth patterns. Observing growth over time will be important.

Will the baby start catching up on the growth chart or will he/she turn out to have Intrauterine Growth Retardation (IUGR)? IUGR indicates a baby who's not growing well inside. It's usually caused by a lack of nutrition or oxygen getting through the placenta to the baby. Sometimes that's caused by smoking, poor nutrition, drug abuse, diabetes, or other medical diagnoses. Something is affecting the placenta.

Sometimes it's the effect of pre-eclampsia, high blood pressure or other circulatory conditions preventing adequate blood flow to and from the placenta. Sometimes, IUGR is caused by genetic anomalies. A lot of the time, we don't know why IUGR happens.

I expect what will happen next is that the doctor will repeat ultrasounds frequently and start monitoring baby's wellbeing with nonstress tests and a fetal heart monitor, either in her doctor's office or at the labor and delivery unit of her hospital. They'll look for specific heart patterns that indicate good fetal circulation and oxygenation.

She may have other tests done as well, like blood work to rule out serious blood pressure issues. If all of these tests turn out reassuring, the doctor will probably just wait and see what happens.

If tests start indicating that baby's in trouble, they'll start talking about contingency plans like bed rest to reduce circulatory stress and check-ups with a perinatologist (who specializes in fetal medicine and premature babies). In the uncertain but less common scenario that the baby is really not growing inside, they'll talk about the possibility of premature delivery. This doesn't happen very often. Most of the time, baby is growing well enough inside Mom that they leave him/her there. When baby is born, they'll keep a close eye on him/her to make sure all systems work well. Most of the time, they're fine. Little but fine.

That's a whole lot to worry about but most of the time smaller than usual babies are just that—little ones. Maybe baby's little because Mom's little. That's why they invented petite sizes. Maybe the mom's not as far along as previously thought and this baby is normal for a 31-weeker. Maybe he/she's just about to hit a growth spurt and will be right where he's supposed to be in another week or so.

If I can offer one useful piece of advice it's this: When people offer you unwanted comments or advice on your pregnancy, stick your fingers in your ears and sing, "LALALALALA! I can't hear you!"

If that's not your style, try saying, "Thanks but I've got a great doctor who's taking good care of me. I'm fine."

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