In humans, a woman becomes pregnant after an ovum and sperm unite (fertilization). after fertilization, a zygote forms. this zygote grows into a fetus after the eighth week of pregnancy. the fetus receives nutrition from the placenta. the umbilical cord connects the fetus and placenta. a sac-like structure, the amniotic sac, envelopes the fetus. the sac contains amniotic fluid, which cushions the fetus and protects it from harm.