The fertilized ovum becomes an embryo, develops into a fetus and gestates until childbirth. It is within the uterus that the fetus develops during gestation. The placenta intermediates the transfer of nutrients between mother and fetus. Many pregnancies with a sirenomelic fetus spontaneously miscarry. If infected during initial stages of pregnancy severe damage to the fetus can take place. Nutrition during pregnancy is important to ensure healthy growth of the fetus. Pregnant women are often excluded due to potential risks to the fetus. The volume of amniotic fluid increases with the growth of fetus. Around the middle of the second trimester, movement of the fetus may be felt. Chromosome characteristics determine the genetic sex of a fetus at conception. Congenital cataracts usually develop as a result of infection of the fetus or genetic reasons. Congenital transmittance from mother to fetus can also occur. She is shown viewing an ultrasound of her fetus with Mason. Spectrometric studies identify androsterone as the main backdoor androgen in the human male fetus. AFP is the most abundant plasma protein found in the human fetus.