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Gestation is the period of
development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking#Development, Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material i ...

development
during the carrying of an
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
, and later
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism tha ...

fetus
, inside
viviparous Among animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aero ...
animals Animals (also called Metazoa) are multicellular Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the L ...

animals
(the embryo develops within the parent). It is typical for
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s, 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 Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple birth, multiple pregnancy involves more than one offspring, ...
. The time interval of a gestation is called the ''
gestation period 300px, A pregnant lioness. In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from Implantation (human embryo), implantation in the uterus through gestation. It begins when a fertilisatio ...
''. In human obstetrics, ''
gestational age Gestational age is a measure of the age of a pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple birth, multiple pregnancy involves more than one offspring, such as w ...
'' refers to the
fertilization age Illustration depicting ovulation and fertilization. Human fertilization is the union of a human egg and sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there ...
plus two weeks. This is approximately the duration since the mother's last menstrual period (LMP) began.


Mammals

In mammals, pregnancy begins when a
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
(fertilized ovum) implants in the female's
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

uterus
and ends once the fetus leaves the uterus during labor or an
abortion Abortion is the ending of a pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young born of living organism, organisms, produced either by a single organism ...

abortion
(whether induced or spontaneous).


Humans

In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from the mother's last missed 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–27th week, and the third trimester is 28th–42nd week. Birth normally occurs at a
gestational age Gestational age is a measure of the age of a pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple birth, multiple pregnancy involves more than one offspring, such as w ...
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 labor Preterm birth (PTB), also known as premature birth, is the birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which ...
and can result from multiple factors, including previous preterm deliveries.
Prenatal care Prenatal care, also known as antenatal care, is a type of preventive healthcare. It is provided in the form of medical checkups, consisting of recommendations on managing a healthy lifestyle and the provision of medical information such as materna ...
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 defect A birth defect, also known as a congenital disorder, is a condition present at birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiat ...
s, 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
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s, the embryo develops inside the body of the mother, as opposed to outside in an
egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do not. eg ...
(
oviparity Oviparous animals are female animals that lay their egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excludi ...
). The mother then gives live birth. The less developed form of viviparity is called
ovoviviparity Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is an outmoded term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparity , viviparous reproduction. Ovoviviparous animals have the embr ...
, in which the mother carries embryos inside eggs. Most
vipers The Viperidae (vipers) are a family of venomous snake Venomous snakes are species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical ...
exhibit ovoviviparity. The more developed form of viviparity is called ; mammals are the best example, but it has also evolved independently in other animals, such as in
scorpion Scorpions are predatory Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including hum ...

scorpion
s, some
shark Sharks are a group of elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, ...

shark
s, and in
velvet worm Onychophora (from Ancient Greek ονυχής, ''onyches'', "claws"; and φέρειν, ''pherein'', "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (aft ...

velvet worm
s. 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
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s develop within
egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do not. eg ...
s 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
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
s are nourished by the
egg yolk Diagram of a chicken egg in its 9th day. Membranes: allantois, chorion, amnion, and vitellus/ yolk. An egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal ha ...

egg yolk
rather than by the mother's body. However, the mother's body does provide
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...

gas exchange
. The young of ovoviviparous
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s are sometimes born as
larva A larva (plural larvae ) is a distinct juvenile form many animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Ove ...
e, and undergo
metamorphosis Metamorphosis is a biological process Biological processes are those processes that are vital for an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are ...
outside the body of the mother. The fish family
Syngnathidae The Syngnathidae is a family of fish which includes seahorses, pipefishes, and seadragons (''Phycodurus'' and ''Phyllopteryx''). The name is derived from Greek, σύν (''syn''), meaning "together", and γνάθος (''gnathos''), meaning "jaw". ...
has the unique characteristic whereby females lay their
eggs Egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do ...
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
seahorse A seahorse (also written ''sea-horse'' and ''sea horse'') is any of 46 species of small marine fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct rel ...

seahorse
s, the
pipefish Pipefishes or pipe-fishes (Syngnathinae) are a subfamily of small fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. They form a sister group to the tunicates ...
, and the and s. Syngnathidae is the only family in the animal kingdom to which the term " male pregnancy" has been applied.


See also

*
Evolution of mammals The evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or s ...
(for the evolution of gestation-related features in humans and other mammals) * Male pregnancy *
Nesting instinct Nesting behaviour refers to an instinct or urge in Pregnancy, pregnant animals associated with an increase of Estradiol, estradiol (E2) to prepare a home for the upcoming newborn(s). Nest building provides protection against predators and competit ...
*
Pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual repr ...

Pregnancy
* Pregnancy in fish *
Prenatal development Prenatal development () includes the development of the embryo and of the foetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of ...

Prenatal development
*
Prenatal nutrition and birth weight Prenatal nutrition addresses nutrient recommendations before and during pregnancy. Nutrition and weight management before and during pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring develops inside ...


References

{{Reflist


External links


NSRL.ttu.edu


Reproduction in mammals