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[Steroids and the prediction of ovulation].


 Prediction of ovulation is useful in artificial insemination but indispensable in gathering of ovocytes for in vitro fertilization (IVF). IVF programs represent quasi-experimental conditions for correlating hormone levels and sonographic findings with ovulation and ovocyte maturation during spontaneous and induced menstrual cycles. During the follicular phase, only 1 "dominant" follicle is usually selected for ovulation. Under the influence of follicle stimulating hormone (FSH) and luteinizing hormone (LH), the ovocyte develops and transforms androgens secreted by the follicle into estrogens. The plasma at this stage is a poor reflector of the hormonal status of the follicular liquid. The preovulatory LH peak occurs after the level of estradiol (E2) reaches 200 pg/ml for about 50 hours. Increased estrogen secretion is the first notable hormonal variation preceding ovulation, but until a stage near ovulation, hormonal changes in the follicular liquid are not reflected in the plasma. Levels of FSH and LH progressively increase at the beginning of the follicular phase. Beginning in the middle of the follicular phase, around the 6th or 7th cycle day, the plasma concentration of 17 beta estradiol begins to increase rapidly. Plasma levels of several other steroids also increase in the days before the LH peak. The androgens produced throughout the menstrual cycle are not all ovarian origin. Their pulsatile secretion and normal variation make them inappropriate for predicting ovulation. Until recently the urinary levels of estrogens were the only measures routinely available, but their reliability as a measure of the estrogen actually produced depended on several factors. They are still used because of their advantages in cost and practicality. Newer tests of plasma estrogen levels give quick results and are used in numerous clinical situations despite their cost and their technical complexity. Although the increased plasma concentration of estradiol is the first of a series of hormonal events leading to ovulation, great variations in E2 rates from 1 cycle to another mean that it is not a reliable or precise predictor of ovulation. For spontaneous cycles, only repeated measurement of plasma or urinary LH levels allow correct prediction of ovulation in clinical practice. Ovarian stimulation by clomiphene or other substances modifies follicular phenomena. In such cases, monitoring of the estradiol level in association with ultrasound provides useful information about follicular maturation and to some extent ovocyte maturation, both of which are essential for IVF and embryo transfer.
