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Gestation

January 10, 2024

See also: Pregnancy

Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous 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]

Drawing of a fetus in utero.

The time interval of a gestation is called the gestation period. In obstetrics, gestational age refers to the time since the onset of the last menses, which on average is fertilization age plus two weeks.[3]

Mammals edit

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 edit

Main article: Pregnancy
 
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.[6] Birth normally occurs at a 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 edit

 
Pregnant scorpion

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 birth. The less developed form of viviparity is called ovoviviparity, in which the mother carries embryos inside eggs. Most vipers exhibit ovoviviparity.[14] The more developed form of viviparity is called 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.[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 animals develop within 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.[21] However, the mother's body does provide gas exchange.[22] The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother.[23]

The fish family Syngnathidae has the unique characteristic whereby females lay their eggs in a brood pouch on the male's chest, and the male incubates the eggs.[24] Fertilization may take place in the pouch or before implantation in the water. Included in Syngnathidae are seahorses, the pipefish, and the weedy and 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 edit

References edit

  1. ^ Mckay RJ, Lucey JF (June 1964). "NEONATOLOGY". The New England Journal of Medicine. 270 (23): 1231–6 CONTD. doi:10.1056/NEJM196406042702306. PMID 14132827.
  2. ^ Keith L, Oleszczuk JJ (January 1999). "Iatrogenic multiple birth, multiple pregnancy and assisted reproductive technologies". International Journal of Gynaecology and Obstetrics. 64 (1): 11–25. doi:10.1016/S0020-7292(98)00230-6. PMID 10190665. S2CID 31814692.
  3. ^ Liao JB, Buhimschi CS, Norwitz ER (June 2005). "Normal labor: mechanism and duration". Obstetrics and Gynecology Clinics of North America. 32 (2): 145–64, vii. doi:10.1016/j.ogc.2005.01.001. PMID 15899352.
  4. ^ "You and your baby at 0-8 weeks pregnant". NHS 111 Wales. NHS Wales. 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. ^ Griggs KM, Hrelic DA, Williams N, McEwen-Campbell M, Cypher R (November 2020). "Preterm Labor and Birth: A Clinical Review". MCN: The American Journal of Maternal/Child Nursing. 45 (6): 328–337. doi:10.1097/NMC.0000000000000656. PMID 33074911. S2CID 224813648.
  8. ^ "Preterm Labor and Birth". www.acog.org. Retrieved 2021-09-13.
  9. ^ Helton MR (March 1997). "Prenatal care". Primary Care. 24 (1): 135–46. doi:10.1016/S0095-4543(22)00091-4. PMID 9016732.
  10. ^ "Gestational age: MedlinePlus Medical Encyclopedia". medlineplus.gov. Retrieved 2021-09-13.
  11. ^ Coley SL, Aronson RE (September 2013). "Exploring Birth Outcome Disparities and the Impact of Prenatal Care Utilization Among North Carolina Teen Mothers". Women's Health Issues. 23 (5): e287–e294. doi:10.1016/j.whi.2013.06.004. PMID 23993476.
  12. ^ a b Gadson, Alexis; Akpovi, Eloho; Mehta, Pooja K. (2017-08-01). "Exploring the social determinants of racial/ethnic disparities in prenatal care utilization and maternal outcome". Seminars in Perinatology. 41 (5): 308–317. doi:10.1053/j.semperi.2017.04.008. ISSN 0146-0005. PMID 28625554.
  13. ^ Gadson A, Akpovi E, Mehta PK (August 2017). "Exploring the social determinants of racial/ethnic disparities in prenatal care utilization and maternal outcome". Seminars in Perinatology. 41 (5): 308–317. doi:10.1053/j.semperi.2017.04.008. PMID 28625554.
  14. ^ Neill WT (1964-01-01). "Viviparity in Snakes: Some Ecological and Zoogeographical Considerations". The American Naturalist. 98 (898): 35–55. doi:10.1086/282299. ISSN 0003-0147. S2CID 85209921.
  15. ^ Bainbridge DR (November 2014). "The evolution of pregnancy". Early Human Development. 90 (11): 741–5. doi:10.1016/j.earlhumdev.2014.08.013. PMID 25242206.
  16. ^ Carter AM, Soma H (August 2020). "Viviparity in the longest-living vertebrate, the Greenland shark (Somniosus microcephalus)". Placenta. 97: 26–28. doi:10.1016/j.placenta.2020.05.014. PMID 32792058. S2CID 221121663.
  17. ^ Smith MR (October 2016). "Evolution: Velvet Worm Biogeography". Current Biology. 26 (19): R882–R884. doi:10.1016/j.cub.2016.07.067. PMID 27728789. S2CID 4039461.
  18. ^ Munns SL, Edwards A, Nicol S, Frappell PB (March 2015). "Pregnancy limits lung function during exercise and depresses metabolic rate in the skink Tiliqua nigrolutea". The Journal of Experimental Biology. 218 (Pt 6): 931–9. doi:10.1242/jeb.111450. PMID 25788728. S2CID 16426853.
  19. ^ Hutchin K (2021-07-19). "Prehensile-tailed Skink". Ambassador Animal. Retrieved 2021-09-19.
  20. ^ Ostrovsky AN, Lidgard S, Gordon DP, Schwaha T, Genikhovich G, Ereskovsky AV (August 2016). "Matrotrophy and placentation in invertebrates: a new paradigm". Biological Reviews of the Cambridge Philosophical Society. 91 (3): 673–711. doi:10.1111/brv.12189. PMC 5098176. PMID 25925633.
  21. ^ Mueller LD, Bitner K (December 2015). "The Evolution of Ovoviviparity in a Temporally Varying Environment" (PDF). The American Naturalist. 186 (6): 708–15. doi:10.1086/683661. PMID 26655978. S2CID 7447706.
  22. ^ Thompson MB (December 2007). "Comparison of the respiratory transition at birth or hatching in viviparous and oviparous amniote vertebrates". Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology. 148 (4): 755–60. doi:10.1016/j.cbpa.2007.01.006. PMID 17314056.
  23. ^ Cook DF, Voss SC, Dadour IR (November 2012). "The laying of live larvae by the blowfly Calliphora varifrons (Diptera: Calliphoridae)". Forensic Science International. 223 (1–3): 44–6. doi:10.1016/j.forsciint.2012.07.015. PMID 22921421.
  24. ^ Scobell SK, Mackenzie DS (June 2011). "Reproductive endocrinology of Syngnathidae". Journal of Fish Biology. 78 (6): 1662–80. doi:10.1111/j.1095-8649.2011.02994.x. PMID 21651522.
  25. ^ Wilson AB, Orr JW (June 2011). "The evolutionary origins of Syngnathidae: pipefishes and seahorses". Journal of Fish Biology. 78 (6): 1603–23. doi:10.1111/j.1095-8649.2011.02988.x. PMID 21651519.
  26. ^ Jones AG, Avise JC (October 2003). "Male pregnancy". Current Biology. 13 (20): R791. doi:10.1016/j.cub.2003.09.045. PMID 14561416.

External links edit

  • Table listing average animal gestation periods

January 10, 2024
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See also Pregnancy Gestation is the period of development during the carrying of an embryo and later fetus inside viviparous 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 Drawing of a fetus in utero The time interval of a gestation is called the gestation period In obstetrics gestational age refers to the time since the onset of the last menses which on average is fertilization age plus two weeks 3 Contents 1 Mammals 1 1 Humans 2 Non mammals 3 See also 4 References 5 External linksMammals editMain 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 edit Main article Pregnancy nbsp Timeline of human fertilizationIn 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 6 Birth normally occurs at a 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 edit nbsp Pregnant scorpionIn viviparous animals the embryo develops inside the body of the mother as opposed to outside in an 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 vipers exhibit ovoviviparity 14 The more developed form of viviparity is called 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 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 animals develop within 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 21 However the mother s body does provide gas exchange 22 The young of ovoviviparous amphibians are sometimes born as larvae and undergo metamorphosis outside the body of the mother 23 The fish family Syngnathidae has the unique characteristic whereby females lay their eggs in a brood pouch on the male s chest and the male incubates the eggs 24 Fertilization may take place in the pouch or before implantation in the water Included in Syngnathidae are seahorses the pipefish and the weedy and 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 editEvolution 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 edit Mckay RJ Lucey JF June 1964 NEONATOLOGY The New England Journal of Medicine 270 23 1231 6 CONTD doi 10 1056 NEJM196406042702306 PMID 14132827 Keith L Oleszczuk JJ January 1999 Iatrogenic multiple birth multiple pregnancy and assisted reproductive technologies International Journal of Gynaecology and Obstetrics 64 1 11 25 doi 10 1016 S0020 7292 98 00230 6 PMID 10190665 S2CID 31814692 Liao JB Buhimschi CS Norwitz ER June 2005 Normal labor mechanism and duration Obstetrics and Gynecology Clinics of North America 32 2 145 64 vii doi 10 1016 j ogc 2005 01 001 PMID 15899352 You and your baby at 0 8 weeks pregnant NHS 111 Wales NHS Wales Retrieved 24 December 2022 What is HCG American Pregnancy Association 2020 04 26 Retrieved 2021 09 13 a b How Your Baby Grows During Pregnancy PDF American College of Obstetricians and Gynecologists Griggs KM Hrelic DA Williams N McEwen Campbell M Cypher R November 2020 Preterm Labor and Birth A Clinical Review MCN The American Journal of Maternal Child Nursing 45 6 328 337 doi 10 1097 NMC 0000000000000656 PMID 33074911 S2CID 224813648 Preterm Labor and Birth www acog org Retrieved 2021 09 13 Helton MR March 1997 Prenatal care Primary Care 24 1 135 46 doi 10 1016 S0095 4543 22 00091 4 PMID 9016732 Gestational age MedlinePlus Medical Encyclopedia medlineplus gov Retrieved 2021 09 13 Coley SL Aronson RE September 2013 Exploring Birth Outcome Disparities and the Impact of Prenatal Care Utilization Among North Carolina Teen Mothers Women s Health Issues 23 5 e287 e294 doi 10 1016 j whi 2013 06 004 PMID 23993476 a b Gadson Alexis Akpovi Eloho Mehta Pooja K 2017 08 01 Exploring the social determinants of racial ethnic disparities in prenatal care utilization and maternal outcome Seminars in Perinatology 41 5 308 317 doi 10 1053 j semperi 2017 04 008 ISSN 0146 0005 PMID 28625554 Gadson A Akpovi E Mehta PK August 2017 Exploring the social determinants of racial ethnic disparities in prenatal care utilization and maternal outcome Seminars in Perinatology 41 5 308 317 doi 10 1053 j semperi 2017 04 008 PMID 28625554 Neill WT 1964 01 01 Viviparity in Snakes Some Ecological and Zoogeographical Considerations The American Naturalist 98 898 35 55 doi 10 1086 282299 ISSN 0003 0147 S2CID 85209921 Bainbridge DR November 2014 The evolution of pregnancy Early Human Development 90 11 741 5 doi 10 1016 j earlhumdev 2014 08 013 PMID 25242206 Carter AM Soma H August 2020 Viviparity in the longest living vertebrate the Greenland shark Somniosus microcephalus Placenta 97 26 28 doi 10 1016 j placenta 2020 05 014 PMID 32792058 S2CID 221121663 Smith MR October 2016 Evolution Velvet Worm Biogeography Current Biology 26 19 R882 R884 doi 10 1016 j cub 2016 07 067 PMID 27728789 S2CID 4039461 Munns SL Edwards A Nicol S Frappell PB March 2015 Pregnancy limits lung function during exercise and depresses metabolic rate in the skink Tiliqua nigrolutea The Journal of Experimental Biology 218 Pt 6 931 9 doi 10 1242 jeb 111450 PMID 25788728 S2CID 16426853 Hutchin K 2021 07 19 Prehensile tailed Skink Ambassador Animal Retrieved 2021 09 19 Ostrovsky AN Lidgard S Gordon DP Schwaha T Genikhovich G Ereskovsky AV August 2016 Matrotrophy and placentation in invertebrates a new paradigm Biological Reviews of the Cambridge Philosophical Society 91 3 673 711 doi 10 1111 brv 12189 PMC 5098176 PMID 25925633 Mueller LD Bitner K December 2015 The Evolution of Ovoviviparity in a Temporally Varying Environment PDF The American Naturalist 186 6 708 15 doi 10 1086 683661 PMID 26655978 S2CID 7447706 Thompson MB December 2007 Comparison of the respiratory transition at birth or hatching in viviparous and oviparous amniote vertebrates Comparative Biochemistry and Physiology Part A Molecular amp Integrative Physiology 148 4 755 60 doi 10 1016 j cbpa 2007 01 006 PMID 17314056 Cook DF Voss SC Dadour IR November 2012 The laying of live larvae by the blowfly Calliphora varifrons Diptera Calliphoridae Forensic Science International 223 1 3 44 6 doi 10 1016 j forsciint 2012 07 015 PMID 22921421 Scobell SK Mackenzie DS June 2011 Reproductive endocrinology of Syngnathidae Journal of Fish Biology 78 6 1662 80 doi 10 1111 j 1095 8649 2011 02994 x PMID 21651522 Wilson AB Orr JW June 2011 The evolutionary origins of Syngnathidae pipefishes and seahorses Journal of Fish Biology 78 6 1603 23 doi 10 1111 j 1095 8649 2011 02988 x PMID 21651519 Jones AG Avise JC October 2003 Male pregnancy Current Biology 13 20 R791 doi 10 1016 j cub 2003 09 045 PMID 14561416 External links editNSRL ttu edu Table listing average animal gestation periods Retrieved from https en wikipedia org w index php title Gestation amp oldid 1191266082, wikipedia, wiki, book, books, library,

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