Gestation

[4] Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL.

[7][8] Prenatal care is important for the maintenance of a healthy pregnancy and surveillance of related complications.

[9] After birth, health care providers will measure the baby's weight, vital signs, reflexes, head circumference, muscle tone, and posture to help determine the gestational age.

[10] Various factors can influence the duration of gestation, including diseases in pregnancy and adequate prenatal care.

[11] The rates of morbidity and pre-existing diseases that predispose mothers to life-threatening, pregnancy-related complications in the United States are increasing.

[14] It was postulated that the rates of DNA damage and senescence may impact the gestation period as well as lifespan.

[14] In viviparous animals, the embryo develops inside the body of the mother, as opposed to outside in an egg (oviparity).

The less developed form of viviparity is called ovoviviparity, in which the mother carries embryos inside eggs.