Gestation

Source: Wikipedia, the free encyclopedia.
See also: Pregnancy
Drawing of a sagittal cross-section of a fetus in the pregnant parent's amniotic cavity.
Drawing of a fetus in utero.

Gestation is the period of

animals (the embryo develops within the parent).[1] 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.[2]

The time interval of a gestation is called the

gestational age refers to the time since the onset of the last menses, which on average is fertilization age plus two weeks.[3]

Mammals

Main article: Pregnancy (mammals)

In mammals, pregnancy begins when a zygote (fertilized ovum) implants in the female's uterus and ends once the fetus leaves the uterus during labor or an abortion (whether induced or spontaneous).

Humans

Main article: Pregnancy
Timeline of human fertilization, ending with implantation of the blastocyst eight to nine days after fertilization.
Timeline of human fertilization

In humans, pregnancy can be defined clinically or biochemically. Clinically, pregnancy starts from first day of the mother's last period.[4] Biochemically, pregnancy starts when a woman's human chorionic gonadotropin (hCG) levels rise above 25 mIU/mL.[5]

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.

gestational age of about 40 weeks, though it is common for births to occur from 37 to 42 weeks.[6] Labor occurring prior to 37 weeks gestation is considered preterm labor and can result from multiple factors, including previous preterm deliveries.[7][8]

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.[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.[12] The brunt of this burden is experienced by non-Hispanic Black women. Inaccessibility of prenatal care may partially explain this ongoing disparity.[12] Other factors that affect prenatal care utilization include socioeconomic status, insurance status, childcare, social support, housing, and immigration status.[13]

Non-mammals

Pregnant scorpion
Pregnant scorpion

In viviparous

velvet worms.[15][16][17] 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.[18][19] The placenta is attached directly to the mother in these lizards which is called viviparous matrotrophy.[20]

Ovoviviparous

metamorphosis outside the body of the mother.[23]

The fish family

leafy sea dragons.[25] Syngnathidae is the only family in the animal kingdom to which the term "male pregnancy" has been applied.[26]

See also

References

  1. PMID 14132827
    .
  2. S2CID 31814692
    .
  3. PMID 15899352
    .
  4. ^ "You and your baby at 0-8 weeks pregnant". NHS 111 Wales. NHS Wales. 26 April 2018. Retrieved 24 December 2022.
  5. ^ "What is HCG?". American Pregnancy Association. 2020-04-26. Retrieved 2021-09-13.
  6. ^ a b "How Your Baby Grows During Pregnancy" (PDF). American College of Obstetricians and Gynecologists.
  7. S2CID 224813648
    .
  8. ^ "Preterm Labor and Birth". www.acog.org. Retrieved 2021-09-13.
  9. S2CID 36322807
    .
  10. ^ "Gestational age: MedlinePlus Medical Encyclopedia". medlineplus.gov. Retrieved 2021-09-13.
  11. PMID 23993476
    .
  12. ^
    PMID 28625554
    .
  13. PMID 28625554
    .
  14. S2CID 85209921
    .
  15. PMID 25242206
    .
  16. S2CID 221121663
    .
  17. S2CID 4039461
    .
  18. S2CID 16426853
    .
  19. ^ Hutchin K (2021-07-19). "Prehensile-tailed Skink". Ambassador Animal. Retrieved 2021-09-19.
  20. PMID 25925633
    .
  21. S2CID 7447706
    .
  22. PMID 17314056
    .
  23. PMID 22921421
    .
  24. PMID 21651522
    .
  25. PMID 21651519
    .
  26. PMID 14561416
    .

External links
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