A common question that many women ask is:
“If I have a big (or small) bump, does this indicate how big or small my baby will be at birth?”
The simple answer is that no, the size of the bump is not directly related to the size of the baby.
There are several reasons that a pregnant woman can have a small or big bump, most of them not an indication of the baby’s actual size:
- Position of the baby (transverse, posterior, breech, engaged or unengaged, sitting back or forward) can all influence the size of the bump.
- Woman’s height. The bump size can vary based on how tall a woman is in some cases, and how much room there is for baby to expand.
- Abdominal muscles. Especially in a first time pregnancy, most women have stronger abdominal muscles which hold the uterus in more. In subsequent pregnancies they’re more likely to have a bigger bump as muscles are weaker (although not always.)
- Body type. Things such as the woman’s BMI, weight gain during pregnancy and genetic history can all impact on how big her bump is.
So how do you tell how big your baby is? The fundal height is a good indicator that your baby is growing to the average and your care provider can check this for you – although babies grow at different rates so the fundal height can measure within a 4 week range without it being a sign of an issue. Ultrasounds are notoriously bad for checking baby’s size and can be anywhere from 10-50% out depending which algorithm is used to determine baby’s size. Although it’s nice to hear an approximation of your baby’s weight, this should almost never be a reason to make a medical decision such as induction or csection.
Susannah is a certified Birth Doula through Childbirth International and the founder of Trimester Talk. With a background in journalism and digital strategy, she combines evidence-based research with real-world knowledge to create accessible content about pregnancy and parenting. She’s a mother of two and stepmother of two more, all of them now teenagers.