A thin-walled sac surrounds the fetus during pregnancy. The sac is filled with amniotic fluid, which protects the fetus from injury.

Many hormone levels are affected in the body during pregnancy, with several hormones playing major roles.

Average weight gain for women is between 25 and 35 pounds, although slight deviations from this may also be considered normal.

Nausea and vomiting are common in the first trimester, as is fatigue. Other common discomforts are hemorrhoids and heartburn.

Some pregnancy changes are caused by hormones. Others are caused by the pressure and weigh of your growing baby.