How Can You Determine Baby's Birth Weight?

Babies just seem to be getting bigger, but will a bigger baby be harder to deliver? Our resident labor nurse answers your questions about baby birth weight.

How Can You Determine Baby's Birth Weight?

It seems to be a big week. I've gotten questions from a couple of readers, Dana and Nicola, who are worried about the size of their babies. Both are first timers and I imagine are concerned that having a "big" baby is a lot more difficult than having a smaller one. Nicola wants to know if her doctor can tell what size her baby will be without doing another ultrasound. Dana has been told her baby will be big and she wonders if that will make her labor too painful for her natural birth plans. Those are good questions. Unfortunately, I don't have an absolute answer.

We hear a lot about big babies these days. They're the reason we do a lot of inductions, c-sections and admissions to the NICU. Babies just seem to be getting bigger. Some of that is certainly genetics. Some of it is uncontrolled diabetes and obesity. Some of it? Who knows? Maybe it's evolution and we're just getting bigger as a species.

I can't tell you how many times we do inductions for "big" babies only to deliver normal sized kiddos. Lots. Doctor's determine their estimate of fetal size based on how big your belly measures. If it measures large for dates, they figure it's going to be a big one. Other reasons for measuring large are extra amniotic fluid or abdominal fat. Ultrasounds are better indicators of fetal size but they're frequently way off. According to the Manual of Obstetrics, the margin of error on determining fetal size ranges between 15 and 30%. That's quite a lot, especially when you're trying to determine how best to delivery this supposedly big baby.

No doubt about it, we're seeing a lot bigger babies than when I first started labor nursing and they play a big part in increased cesarean section rates. To answer (sort of) Nicola's question about whether her doctor can determine her baby's size/weight without ultrasound—he can make a very educated guess. He's been measuring your belly at every appointment and tracking your growth rate. He can palpate (press on and feel around) your tummy to feel for your baby's general size and from there come up with a darn good guess. That's all it is though—a darn good guess.

Dana was told after an ultrasound that her baby is big and she's worried about pain and whether she'll be able to get this baby out vaginally. I don't know that big-baby-labors are any more painful than average-baby-labors. Pain is such a subjective thing that I don't think we can measure accurately if one labor is more painful than another. There are too many factors like tolerance to pain, ability to relax, previous experiences with pain and/or trauma. Whatever measures you're taking to prepare for your natural (unmedicated) labor will be good enough. I hope you're taking childbirth preparation classes and practicing with your partner. Then go into labor with an open mind and hope for the best. Like any labor, there are no guarantees that things will go as planned. Big or small, some babies don't like labor and need to be delivered by "alternative means." Though more extremely big babies are born by cesarean than others, lots and lots of biggun's come out vaginally. Sure, there are likely to be more pereneal tears, bruises and swelling but they're easy enough to repair and most women recover beautifully.

I hate to get on my soapbox about diet and exercise again but the best way to deliver a healthy weight baby (and bigger is not always healthier) is to eat well, exercise and avoid excess weight gain. Extremely big babies have a harder time transitioning to life outside the uterus. They have less stable blood sugar, more respiratory and temperature control issues. They're more likely to spend a little time in the nursery with an IV and oxygen, recovering and stabilizing during their transition. Most eventually do just fine but still, no one likes it when their baby has to go to the nursery.

Dana, I hope your plans and hopes for a "natural" labor go smoothly but keep in mind that the ultimate goal is a healthy baby and mom. If it just plain gets too painful for you, there are lots of options for pain management. Talk to your midwife about this well before you go into labor. Nicola, here's wishing you a good sized, but not too big, baby and a wonderful birth. Keep those questions coming, ladies. I love them.