Normal Fetal Development

The Baby's Size
Sometimes women express concern about giving birth to a large baby. Many factors affect how big your baby will be. If you are in good health, have no medical problems and take good care of yourself during pregnancy, you'll probably have an average-size baby. Although weight varies greatly from baby to baby, the average baby at term weighs 7 to 7 ½  pounds (3,280 to 3,400 g).
Some factors do affect the size of a baby at birth, including hypertension and diabetes, which are more common in older pregnant women. Hypertension during pregnancy can cause intrauterine-growth restriction (IUGR), which results in smaller babies. Diabetes can cause blood-sugar problems. Blood-sugar levels are higher in those with gestational diabetes or mild diabetes that is not under control. Diabetes exposes the baby to higher sugar levels, resulting in a larger baby.

In cases of insulin-dependent diabetes, the result may be a smaller baby. Women with insulin-dependent diabetes may have circulation problems, which can result in IUGR and decreased blood flow to the baby.

THE FETAL ENVIRONMENT
Your baby is growing and developing inside a complex system within your body. There are three major parts to this system, and each relies upon the other to work together as a complete unit. Your baby's first home consists of the placenta, the umbilical cord and the amniotic sac. Together they provide nourishment, warmth and protection while your baby matures and prepares to live on its own, outside your uterus.