Zimmermann MB: The efects of iodine deiciency in pregnancy and infancy.
Paediatr Perinat Epidemiolr26(Supp 1):108,r2012
OMETRIAL CYCLE. . .... 80
DECIDUA. . .... 85
FORMATION.. ............ . . .... 87
PLACENTA AND CHORION . .90
AMNION . . .... 95
UMBILICAL CORD ................... . . .... ..... 97
PLACENTAL HORMONES. .98
INTERACTIONS. . . . . .... . . . . . . ...... . . . . . .. . ... 104
Almost immediately ater the impamltio1 of the ovum, its trophoblast begins to prolerate and lJ1d, the s.rrounding decidual tissue. As it does so, it breaks through the walls of the moumal capilaries, from which the blood escapes and orms cavities, which are bounded party by trophobast and party by decidua. ?he maternal blood spaces established in this manner represent the earliest stages of the intervillous blood spaces of the inure placenta.
-). Whitridge Williams (1903)
In 1903, the histopathological and embryological descrip tions of ovum implanrarion and placental development had been extensively studied and described. However, the origins and functions of pregnancy hormones were largely unknown. Indeed, it was another 25 to 30 years before estrogen and progesterone were discovered. In the past 50 years, remarkable strides have followed to uncover the steps of implantation and placental structure and function.
All obstetricians should understand the basic biological steps required for women to successully achieve pregnancy. Several abnormalities can fect each of these and lead to infertili' or pregnancy loss. In most women, spontaneous, cyclical ovulation continues during almost 40 years between menarche and menopause. Without contraception, there are approximately 400 opportunities for pregnancy, namely, the day of ovulation and its few preceding days. his narrow window for fertilization is controlled by tightly regulated production of ovarian steroids. Moreover, these hormones promote optimal endometrial regeneration after menstruation in preparation for the next implantation window.
If fertilization occurs, events thac begin ater blastocyst implantation persist until parturition. hese derive from a unique interaction between fetal trophoblasts and the maternal endometrium. which has been transformed into the decidua. The ability of a mother and her fetus to coexist as two distinct immunological systems results from endocrine. paracrine. and immunological modiication of fetal and maternal tissues in a manner not seen elsewhere. In addition. the placenta mediates a unique fetal-maternal communication system. which creates a hormonal environment that initially maintains pregnancy and eventually initiates events leading to parturition.
Predictable. regular. cyclical. and spontaneous ovulatory menstrual cycles are regulated by complex interactions of the hypothalamic-pituitay-ovarian axis. Concurrently, cyclical changes in endometrial histology are faithfully reproduced ;-1). Essentials players in this process include follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are pituitary-derived gonadotropins, and the ovarian sex steroid hormones estrogen and progesterone.