In return, fetus give placenta what it lacks (19 Carbon compounds)-precursor of oestrogen. Fetus lacks 3 B hydroxysteroid dehydrogenase-hence unable to produce progesterone-borrows from placenta. Hormones act as catalysts for chemical changes at the cellular level that are necessary for growth, development and energy. In its key location as a way station between mother and fetus, placenta can use precursors from either mother or fetus to circumvent its own deficiencies in enzyme activities. To bypass this deficit, dehydroisoandrosterone sulfate (DHA) from the fetal adrenal is converted to estradiol-17ί by trophoblasts. Human trophoblast lack 17-hydroxylase and therefore cannot convert C21-steroids to C19-steroids, the immediate precursors of oestrogen. The placenta does not have all the necessary enzymes to make oestrogens from cholesterol, or even progesterone. Studies have shown that the human corpus luteum makes significant amounts of estradiol, but it is progesterone and not oestrogen that is required for successful implantation. And, of course, progesterone prepares and maintains the endometrium to allow implantation earlier. Progesterone is also important in suppressing the maternal immunologic response to fetal antigens, thereby preventing maternal rejection of the trophoblast. This is relevant to understand prevention of preterm labor. However, beginning about the 32 nd week there is a second, more gradual rise in 17a-hydroxyprogesterone due to placental utilization of fetal precursors. By the tenth week of gestation, this compound has returned to baseline levels, indicating that the placenta has little 17a hydroxylase activity. In early pregnancy, the maternal levels of 17 a-hydroxyprogesterone rise, marking the activity of the corpus luteum. Progesterone production is independent of he precursor available, fetal status including the wellbeing. Almost all of the progesterone produced by the placenta enters the placenta, contrast to oestrogen. 2 When the pregnancy reaches term gestation, progesterone levels range from 100-200 ng/ml and the placenta produces about 250 mg/day. The fetoplacental unit was competent from 10 to 12 weeks’ gestation. 1 A study in ovarian failure and Assisted reproduction it was shown that one hundred mg of P were probably a supraphysiological dose to support pregnancy 6 to 8 weeks after conception. Progesterone is largely produced by the corpus luteum until about 10 weeks of gestation. Method of locating review: Pubmed, scopus Thyroid disorders have a great impact on pregnancy outcome and needs to be monitored and treated accordingly. The route of administration plays an important role in the drug's safety and efficacy profile in different trimesters of pregnancy. Preterm labor can be prevented by the use of progestogen. Prophylactic hormonal supplementation can be recommended for all assisted reproduction techniques cycles. Supportive care in early pregnancy is associated with a significant beneficial effect on pregnancy outcome. Progesterone has been shown to stimulate the secretion of Th2 and reduces the secretion of Th1 cytokines which maintains pregnancy. The controversies of use of progestogen and others are discussed in this chapter. Progesterone and oestrogen have a great role along with other hormones. The endocrinology of human pregnancy involves endocrine and metabolic changes that result from physiological alterations at the boundary between mother and fetus.
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