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Gestation is the period of
In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from first day of the mother's last period. Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL.
Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third trimester is 29/30th–42nd week. Birth normally occurs at a
In viviparous animals, the embryo develops inside the body of the mother, as opposed to outside in an Egg (biology), egg (oviparity). The mother then gives live birth. The less developed form of viviparity is called ovoviviparity, in which the mother carries embryos inside eggs. Most Viperidae, vipers exhibit ovoviviparity. The more developed form of viviparity is called placenta, placental viviparity; mammals are the best example, but it has also evolved independently in other animals, such as in scorpions, some sharks, and in velvet worms. Viviparous offspring live independently and require an external food supply from birth. Certain lizards also employ this method such as the genera ''Tiliqua'' and ''Corucia.'' The placenta is attached directly to the mother in these lizards which is called viviparous matrotrophy.
Ovoviviparous animals develop within Egg (biology), eggs that remain within the mother's body up until they hatch or are about to hatch. It is similar to viviparity in that the embryo develops within the mother's body. Unlike the embryos of viviparous species, ovoviviparous embryos are nourished by the egg yolk rather than by the mother's body. However, the mother's body does provide gas exchange. The young of ovoviviparous amphibians are sometimes born as larvae, and undergo Metamorphosis (biology), metamorphosis outside the body of the mother.
The fish family Syngnathidae has the unique characteristic whereby females lay their egg (biology), eggs in a brood pouch on the male's chest, and the male incubates the eggs. Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy sea dragon, weedy and leafy sea dragons. Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.
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Reproduction in mammals
development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
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during the carrying of an embryo, and later fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
, inside viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
animals
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
(the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth
A multiple birth is the culmination of one multiple pregnancy, wherein the mother gives birth to two or more babies. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such bir ...
.
The time interval of a gestation is called the '' gestation period''. In obstetrics, ''gestational age
In obstetrics, gestational age is a measure of the age of a pregnancy which is taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Su ...
'' refers to the time since the onset of the last menses
Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of horm ...
, which on average is Human fertilization#Fertilization age, fertilization age plus two weeks.
Mammals
In mammals, pregnancy begins when a zygote (fertilized ovum) Implantation (embryology), implants in the female's uterus and ends once the fetus leaves the uterus during labor or an abortion (whether induced or spontaneous).Humans
In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from first day of the mother's last period. Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL.
Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third trimester is 29/30th–42nd week. Birth normally occurs at a gestational age
In obstetrics, gestational age is a measure of the age of a pregnancy which is taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Su ...
of about 40 weeks, though it is common for births to occur from 37 to 42 weeks. Labor occurring prior to 37 weeks gestation is considered Preterm birth, preterm labor and can result from multiple factors, including previous preterm deliveries.
Prenatal care is important for the maintenance of a healthy pregnancy and surveillance of related complications. In high-income countries, prenatal care typically involves monthly visits during the first two trimesters, with an increasing number of visits closer to delivery. At these visits, healthcare providers will evaluate a variety of parental and fetal metrics, including fetal growth and heart rate, birth defects, maternal blood pressure, among others.
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.
Various factors can influence the duration of gestation, including diseases in pregnancy and adequate prenatal care. The rates of morbidity and pre-existing diseases that predispose mothers to life-threatening, pregnancy-related complications in the United States are increasing. The brunt of this burden is experienced by non-Hispanic Black women. Inaccessibility of prenatal care may partially explain this ongoing disparity. Other factors that affect prenatal care utilization include socioeconomic status, insurance status, childcare, social support, housing, and immigration status.
Non-mammals
In viviparous animals, the embryo develops inside the body of the mother, as opposed to outside in an Egg (biology), egg (oviparity). The mother then gives live birth. The less developed form of viviparity is called ovoviviparity, in which the mother carries embryos inside eggs. Most Viperidae, vipers exhibit ovoviviparity. The more developed form of viviparity is called placenta, placental viviparity; mammals are the best example, but it has also evolved independently in other animals, such as in scorpions, some sharks, and in velvet worms. Viviparous offspring live independently and require an external food supply from birth. Certain lizards also employ this method such as the genera ''Tiliqua'' and ''Corucia.'' The placenta is attached directly to the mother in these lizards which is called viviparous matrotrophy.
Ovoviviparous animals develop within Egg (biology), eggs that remain within the mother's body up until they hatch or are about to hatch. It is similar to viviparity in that the embryo develops within the mother's body. Unlike the embryos of viviparous species, ovoviviparous embryos are nourished by the egg yolk rather than by the mother's body. However, the mother's body does provide gas exchange. The young of ovoviviparous amphibians are sometimes born as larvae, and undergo Metamorphosis (biology), metamorphosis outside the body of the mother.
The fish family Syngnathidae has the unique characteristic whereby females lay their egg (biology), eggs in a brood pouch on the male's chest, and the male incubates the eggs. Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy sea dragon, weedy and leafy sea dragons. Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.
See also
*Evolution of mammals (for the evolution of gestation-related features in humans and other mammals) *Male pregnancy *Nesting instinct *Pregnancy *Pregnancy in fish *Prenatal development *Prenatal nutrition and birth weightReferences
{{ReflistExternal links
NSRL.ttu.edu
Reproduction in mammals