For my first son I gained 31 pounds and he came out 8 pounds 7 oz and my doctor told me I was measuring small so he would be a small baby. Now I’m 15 wks along with my second and my same doctor is telling I’m 2.5 inches bigger than I am supposed to be. Does that mean this baby is going to be even bigger then my first? I’m 5″4 and normally 113 pounds and have a very small frame. My first son being 8 pds 7 oz. was pretty big I thought so I’m a little scared.”
As you can see from your doctor’s predictions, measurements of a fetus’ size from the outside are basically vague of guesstimates, especially if you doctor is talking about the measurement outside of your stomach and not of an ultrasound.
There are lots of reasons why a uterus might appear to measure large for date in a second pregnancy. Abdominal muscles get weakened by a first pregnancy, making for a less-firm bump. Fibroids, a full bladder or simple mis-measuring can also cause a measurement not to match up with a due date. Even fetal size estimates made late in pregnancy by experienced experts with the help of ultrasound can be off by a good percentage.
It’s quite possible, too, that your second baby will be larger than the first. But there’s no way to know that with certainty so early in your pregnancy. Remember, too, that it’s the proportion of the baby’s head circumference to your pelvic outlet that might make birth difficult, not the baby’s weight or length.