Mammals [edit ]
In mammals, pregnancy begins when a zygote ( fertilize ovum ) implants in the female ‘s uterus and ends once the fetus leaves the uterus during department of labor or an abortion ( whether induced or spontaneous ).
Humans [edit ]
timeline of homo fertilization In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from the mother ‘s last miss period. Biochemically, pregnancy starts when a charwoman ‘s human Chorionic Gonadotropin ( human chorionic gonadotropin ) levels rise above 25 mIU/mL. [ 4 ] human pregnancy can be divided into three trimesters, each approximately three months long : the beginning, second, and one-third trimester. The first clean-cut is from the last menstrual period through the thirteenth week, the second gear clean-cut is 14th–27th week, and the third base clean-cut is 28th–42nd week. [ 5 ] Birth normally occurs at a gestational senesce of about 40 weeks, though it is common for births to occur from 37 to 42 weeks. [ 5 ] Labor occurring anterior to 37 weeks pregnancy is considered preterm parturiency and can result from multiple factors, including former preterm deliveries. [ 6 ] [ 7 ] Prenatal manage is crucial for the sustenance of a healthy pregnancy and surveillance of relate complications. In high-income countries, prenatal wish typically involves monthly visits during the first gear two trimesters, with an increasing numeral of visits closer to delivery. At these visits, healthcare providers will evaluate a variety of parental and fetal metrics, including fetal increase and affection rate, birth defects, maternal blood pressure, among others. [ 8 ]
After birth, health care providers will measure the baby ‘s weight, full of life signs, reflexes, head circumference, muscle tone, and position to help determine the gestational historic period. [ 9 ] diverse factors can influence the duration of gestation, including diseases in pregnancy and adequate prenatal care. [ 10 ] The rates of unwholesomeness and preexistent diseases that predispose mothers to dangerous, pregnancy-related complications in the United States are increasing. [ 11 ] The brunt of this charge is experienced by non-Hispanic Black women. Inaccessibility of prenatal care may partially explain this ongoing disparity. [ 11 ] other factors that affect prenatal manage utilization include socioeconomic condition, indemnity condition, childcare, social support, caparison, and immigration condition. [ 12 ]
In viviparous animals, the embryo develops inside the body of the mother, as opposed to outside in an egg ( oviparity ). The mother then gives live give birth. The less build up human body of viviparity is called ovoviviparity, in which the beget carries embryos inside eggs. Most vipers exhibit ovoviviparity. [ 13 ] The more develop kind of viviparity is called placental viviparity ; mammals are the best case, but it has besides evolved independently in other animals, such as in scorpions, some sharks, and in velvet worms. [ 14 ] [ 15 ] [ 16 ] Viviparous offspring alive independently and require an external food provide from parentage. Certain lizards besides employ this method such as the genus Tiliqua and Corucia. [ 17 ] [ 18 ] The placenta is attached immediately to the mother in these lizards which is called viviparous matrotrophy. [ 19 ] ovoviviparous animals develop within eggs that remain within the mother ‘s soundbox up until they hatch or are about to hatch. It is alike to viviparity in that the embryo develops within the mother ‘s body. Unlike the embryo of viviparous species, ovoviviparous embryo are nourished by the egg yolk preferably than by the mother ‘s body. [ 20 ] however, the mother ‘s body does provide gasoline exchange. [ 21 ] The young of ovoviviparous amphibians are sometimes born as larva, and undergo transfiguration outside the consistency of the beget. [ 22 ] The fish syndicate Syngnathidae has the singular characteristic whereby females lay their eggs in a sulk pouch on the male ‘s chest of drawers, and the male incubates the eggs. [ 23 ] Fertilization may take home in the pouch or before implantation in the body of water. Included in Syngnathidae are seahorses, the pipefish, and the scraggy and leafy ocean dragons. [ 24 ] Syngnathidae is the only family in the animal kingdom to which the term “ male pregnancy “ has been applied. [ 25 ]