The physiological basis of the fertile period
Definition of the fertile phase of the menstrual cycle is based on the probability that coitus during that period will result in pregnancy, or, alternatively, that coitus outside that period is very unlikely to be fertile. The most significant determinant of the location of the fertile phase within the cycle is the timing of ovulation1: because of the limited fertilizable life-span of the ovum, the fertile period ends shortly after ovulation, but begins a variable number of days before that event, depending on the fertilizing life-span of the spermatozoa. Ovarian oestradiol-17ß (E2) is the physiological basis of the onset and duration of the fertile period: it plays a central role in follicular development and oocyte maturation, is involved in ovum transport, and is responsible for endometrial proliferation and preparation for implantation, stimulation of the cervical mucus glands to secrete a fluid favourable to sperm survival and transport, and facilitation of the mid-cycle surge of luteinizing hormone (LH) which precipitates ovulation. It may enhance female receptivity to the male. The central role of E2 is reflected in the extensive use that is made of oestrogen assays, and of observations of oestrogen-induced phenomena in the clinical delineation of the fertile period. The intervals between fertile periods are determined by corpus luteum function and by breast feeding.
KeywordsLuteinizing Hormone Menstrual Cycle Granulosa Cell Follicular Fluid Follicular Phase
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