Your doctor measures your abdomen during prenatal visits to get a very rough estimate of the size of the baby. After 20 weeks, the distance from the pubic bone up over the top of the uterus is on average about the same number of centimeters as weeks’ gestation, give or take 4 centimeters. This number provides a rough estimate of fetal growth, but is also influenced by the mother’s height and weight, the amount of amniotic fluid, the position of the baby and how many babies are in there.
So what does it mean if you measure larger than expected? It could be one of several things:
If you have not yet had an ultrasound, a larger than expected uterus can be a sign of a twin pregnancy, or that you are further along than expected. Ultrasound is very good at assessing the number of babies, though, so once you have had a good professional ultrasound that only saw one baby, you are very unlikely to be carrying twins. And the earliest ultrasound is the most accurate for gestational age, so again if you already had an ultrasound, wrong dates are an unlikely cause of measuring big.
Often a large measurement is just a reflection on how you are carrying the baby. Also if you are heavy the measurement may be several centimeters bigger than it otherwise would be, since the distance measured is affected by the thickness of the abdominal wall.
Larger size can be caused by excess amniotic fluid. This in turn may be caused by maternal diabetes or by a problem that the baby has with swallowing, or it may be just a random meaningless finding. If excess fluid is found, your doctor will tell you more about it.
The baby may be extra big. Babies may become extra large when the mother has uncontrolled diabetes, if she herself is large, or if she has gained excessive weight during the pregnancy, or it can just be a random event. A larger baby means that a Cesarean section is more likely, although most babies, unless they are expected to be over 10 or 11 pounds, can still deliver vaginally.
What can you do to slow down the growth of a big baby? Normal weight gain and, if you are diabetic, good control of blood glucose are the only safe tactics. You should not starve yourself when you are pregnant! Interestingly, although you might think that inducing labor would make for a better birth (since the baby wouldn’t get even bigger) it turns out that induction itself can create problems with delivery, and doesn’t seem to decrease the chance of needing a C-section.
Answered by Dr. Marjorie Greenfield