Abstract
In most mammalian species lactation suppresses fertility. There is no doubt
that it is the suckling stimulus that provides the controlling signal, and, in
human reproduction, this is the only truly physiological signal that
suppresses fertility in normally nourished, healthy women. In breastfeeding
women, the return of normal fertility follows a relatively well-defined path
progressing through: an almost complete inhibition of gonadotrophin-releasing
hormone/luteinizing hormone (GnRH/LH) pulsatile secretion in the early
stages of lactation; return of erratic pulsatile secretion with some ovarian
follicle development associated with increases in inhibin B and oestradiol; a
resumption of apparently normal follicle growth associated with a normal
increase in oestradiol, but often an absence of ovulation, or formation of an
inadequate corpus luteum; and a return to normal ovulatory menstrual cycles. A
key element in controlling the rate of this progression is the impact of the
suckling stimulus on the GnRH pulse generator, a common feature of lactation
in those species for which there is information. The variability in the
duration of lactational amenorrhoea between women is related to the variation
in the strength of the suckling stimulus, a unique situation between each
mother and baby. Full breastfeeding can provide a reliable contraceptive
effect in the first 6 to 9 months, but the precise mechanisms whereby the
suckling stimulus affects GnRH pulsatile secretion remain unknown. Many
studies on the hypothalamic pathways that might be involved in the translation
of the neural suckling stimulus to suppression of hypothalamic GnRH secretion
have been undertaken, principally in rats. In women, suckling increases the
sensitivity of the hypothalamus to the negative feedback effect of oestradiol
on suppressing the GnRH/LH pulse generator, a mechanism that appears to be
common across species. In contrast, the role of prolactin in the control of
GnRH appears to be species-dependent, with the importance varying from none to
an important role in late or throughout lactation. In women, there is little
evidence for a role of leptin, opioids or dopamine, although this may merely
reflect the ethical dilemma of being able to give sufficient drug to test the
system in the mother since these drugs will pass through the breast milk to
the baby. Regardless of mechanism, practical guidelines for using
breastfeeding as a natural contraceptive have been developed, which allows
mothers to utilize the only natural suppressor of fertility in women as an
effective means of spacing births.
Subject
Developmental Biology,Endocrinology,Genetics,Molecular Biology,Animal Science and Zoology,Reproductive Medicine,Biotechnology
Cited by
198 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献