Pregnant woman sitting in chair reading. Baby is visible inside. Placenta and umbilical cord send nourishment to baby. Amniotic sac (bag of water) holds fluid that surrounds baby in uterus. Perineum is area between vaginal opening and anus. Uterus (womb) holds baby as it grows. Mucous plug helps keep bacteria out of uterus. Cervix is narrow opening of uterus. Pubic symphysis joint lies between pelvic bones and allows baby to pass through. Vagina is birth canal.