A: Babies grow tremendously in the later stages of pregnancy -- they usually double in size between 28 weeks and the time they're born. But it's rare that a baby is growing too fast; more likely, he's just big for other reasons. A baby is not considered too large unless his growth exceeds the 90th to 95th percentile (as calculated by an ultrasound, which examines the circumference around the belly and head as well as length of her legs).
If you're concerned about the size of your baby, first look at your and your husband's genetics. If one or both of you is tall or big-boned, then having a large baby could be normal for you. However, if you're gaining a lot of weight (for most women pregnant with one child, doctors recommend gaining 25 to 35 pounds), this could be making your baby bigger than she ought to be. Your doctor can advise you whether your weight gain and diet are healthy and what, if anything, you should be doing differently.
The only real cause for concern is if your baby is too big as a result of your having gestational diabetes, which your doctor would be able to diagnose with ultrasounds and blood tests. When you develop diabetes during pregnancy, your baby receives higher amounts of sugar than normal, causing her to be bigger than she normally would. If you have gestational diabetes, it's important to keep it in under control with a proper diet (your doctor can provide you with healthy-eating tips) and, if necessary, medication to regulate insulin production.