Even though I've birthed two babies that were essentially the same size, my husband still occasionally brings up how different I looked between the two. With our first, I was barely able to reach my steering wheel and even with all the extra girth, our son was born early. With our daughter, I don't think I even needed to adjust the bucket seat in my car. But throughout both pregnancies, my bump's fundal height measured very consistently, despite the fact that one made me feel like a major landmass and the other was so compact. So what is fundal height and what does it mean?
According to the Mayo Clinic, fundal height is the measurement in centimeters between your pubic bone and the top of your uterus, or fundus. Beginning in the second trimester, an obstetrician will begin measuring you at each appointment to be sure your bump falls within a short range of measurements that should correlate to how many weeks along you are. For instance, if you're sitting pretty at 30 weeks, your fundus should measure pretty close to 30 centimeters from your pubic bone.
"Once you’re out of the first trimester, you should be growing about one centimeter a week," says Ashlyn Biedbach, an RN and doula in Denton, Texas, to Romper. "Usually it’s the most accurate when you’re actually showing more [than] just a little pouch like some moms get at the beginning."
Fundal height can indicate a few things. First, remember how you were asked the date of your last period at your first prenatal appointment? That date is used to estimate the baby's due date, not it's actual conception because ovulation can be more difficult to pinpoint. If you're measuring large for your gestational age, your due date might be off.
Under- or over-development of a bump could also indicate issues with amniotic fluid, Biedebach says. It could boil down simply to being dehydrated or over-hydrated, but the doctor is also going to perform an ultrasound in case to double-check the infant and the amount of fluid in utero. But there could be a more serious problem, too.
"If there’s enough and then all of a sudden there’s too much, the baby's kidneys sometimes aren't filtering the fluid how they should be," she says.
There are different things that can affect how bumps present though, despite their healthy measurements. Biedebach says a lot of it has to do with the mother's body shape and height, how the baby is situated in the womb, and even skeletal alignment. Sometimes, she says, a body going through a pregnancy for the first time can react in different ways to structural changes.
"The measurement should still be consistent with however many weeks she is, but if she has a short torso for example, her bump will just look different. It could just be that the uterus is hidden because she's super tall, or can be prominent if she's 4' 11"," she says. "It could be how baby is situated in utero — they could be laying toward the front or back. Spinal alignment can also make a huge difference and chiropractic adjustment can change appearance of bump."
According to Babble, measuring fundal height was a more crucial means of determining fetal health in the days before routine ultrasounds and has only a limited applications these days. In fact, some doctors don't even record it in their patient's charts anymore, but pull out the measuring tape to see if more accurate tests are necessary. A lot of the time, fundal height will be affected by things like fetal position, whether the baby has dropped, and whether it's a multiples pregnancy.
What's always true is that every woman and every pregnancy is unique, and as long as your bump is growing at a consistent rate within a specific range, you have very little to worry about if you're feeling insecure about its size. Don't give it a second thought until your doctor does — just find someone to tie your shoes in the meantime.
Ashlyn Biedbach, RN and doula
Editor's note: This post has been updated from its original version