The initiation of parturition at term

Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
Obstetrics and Gynecology Clinics of North America (Impact Factor: 1.38). 01/2005; 31(4):935-47, xii. DOI: 10.1016/j.ogc.2004.08.012
Source: PubMed


This article discusses the initiation of parturition at term.

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    • "Another function is to stimulate the maternal adrenal gland and the transitional zone of the fetal adrenal gland (both directly and through stimulation of the fetal pituitary) to synthesize and release cortisol. Cortisol serves to drive the maternal–placental–fetal adrenal axis through a positive feedback system [Robinson et al., 1988], which results in increasing estrogen production over gestation [Lockwood, 2004; Rainey et al., 2004]. Maternal cortisol also is likely involved in many of the metabolic adjustments necessary for successful pregnancy , such as the increase in maternal metabolic rate and insulin resistance [Damjanovic et al., 2009]. "
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    ABSTRACT: The anthropoid primate placenta appears to be unique in producing corticotropin-releasing hormone (CRH). Placental CRH is involved in an endocrine circuit key to the production of estrogens during pregnancy. CRH induces cortisol production by the maternal and fetal adrenal glands, leading to further placental CRH production. CRH also stimulates the fetal adrenal glands to produce dehydroepiandrostendione sulfate (DHEAS), which the placenta converts into estrogens. There are at least two patterns of maternal circulating CRH across gestation among anthropoids. Monkeys examined to date (Papio and Callithrix) have an early-to-mid gestational peak of circulating CRH, followed by a steady decline to a plateau level, with a possible rise near parturition. In contrast, humans and great apes have an exponential rise in circulating CRH peaking at parturition. To further document and compare patterns of maternal circulating CRH in anthropoid primates, we collected monthly blood samples from 14 squirrel monkeys (Saimiri boliviensis) and ten owl monkeys (Aotus nancymaae) during pregnancy. CRH immunoreactivity was measured from extracted plasma by using solid-phase radioimmunoassay. Both squirrel and owl monkeys displayed a mid-gestational peak in circulating CRH: days 45-65 of the 152-day gestation for squirrel monkeys (mean±SEM CRH=2,694±276 pg/ml) and days 60-80 of the 133-day gestation for owl monkeys (9,871±974 pg/ml). In squirrel monkeys, circulating CRH declined to 36% of mean peak value by 2 weeks before parturition and then appeared to increase; the best model for circulating CRH over gestation in squirrel monkeys was a cubic function, similar to previous results for baboons and marmosets. In owl monkeys, circulating CRH appeared to reach plateau with no subsequent significant decline approaching parturition, although a cubic function was the best fit. This study provides additional evidence for a mid-gestational peak of maternal circulating CRH in ancestral anthropoids that has been lost in the hominoid lineage.
    Full-text · Article · Nov 2010 · American Journal of Primatology
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    • "Placental CRH plays key roles in the progression of gestation to parturition (Majzoub et al., 1999; Challis et al., 2000). It is thought to be important in the transition from uterine quiescence to coordinated contractions, and in fetal development and maturation necessary for extrauterine life (Majzoub et al., 1999; Lockwood, 2004; Smith et al., 2005). CRH is a prime example of an important regulatory molecule that, through evolution, has come to serve a wide range of adaptive functions. "
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    ABSTRACT: Corticotropin-releasing hormone (CRH) is an ancient regulatory molecule. The CRH hormone family has at least four ligands, two receptors, and a binding protein. Its well-known role in the hypothalamic-pituitary-adrenal (HPA) axis is only one of many. The expression of CRH and its related peptides is widespread in peripheral tissue, with important functions in the immune system, energy metabolism, and female reproduction. For example, CRH is involved in the implantation of fertilized ova and in maternal tolerance to the fetus. An apparently unique adaptation has evolved in anthropoid primates: placental expression of CRH. Placental CRH stimulates the fetal adrenal zone, an adrenal structure unique to primates, to produce dehydroepiandrosterone sulfate (DHEAS), which is converted to estrogen by the placenta. Cortisol induced from the fetal and maternal adrenal glands by placental CRH induces further placental CRH expression, forming a positive feedback system that results in increasing placental production of estrogen. In humans, abnormally high placental expression of CRH is associated with pregnancy complications (e.g., preterm labor, intrauterine growth restriction (IUGR), and preeclampsia). Within anthropoid primates, there are at least two patterns of placental CRH expression over gestation: monkeys differ from great apes (and humans) by having a midgestational peak in CRH expression. The functional significance of these differences between monkeys and apes is not yet understood, but it supports the hypothesis that placental CRH performs multiple roles during gestation. A clearer understanding of the diversity of patterns of placental CRH expression among anthropoid primates would aid our understanding of its role in human pregnancy.
    Full-text · Article · Jul 2006 · American Journal of Human Biology
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    ABSTRACT: Interfering with the normal physiological process of labor and birth in the absence of medical necessity increases the risk of complications for mother and baby. Six evidence-based care practices promote physiological birth: avoiding medically unnecessary induction of labor, allowing freedom of movement for the laboring woman, providing continuous labor support, avoiding routine interventions and restrictions, encouraging spontaneous pushing in nonsupine positions, and keeping mothers and babies together after birth without restrictions on breastfeeding. Nurses are in a unique position to provide these care practices and to help childbearing women make informed choices based on evidence.
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