The disappearance of HCG and return of pituitary function after abortion.

Plasma concentrations of HCG/LH and FSH were monitored after a first trimester abortion in eighteen healthy female volunteers three times weekly until the onset of first menstruation. Plasma concentrations of the HCG were measured with a specific RIA for the beta subunit (beta-sub-HCG) from the samples of six of these subjects. The elimination of HCG during the first 12 days was studied from plasma concentrations measured by the radioimmunoassay of LH. The experimental data were well explained by a mathematical model consisting of three exponentially decreasing components. The half-lives of the two more slowly decreasing components were 27 and 168 h. The estimate of the complete disappearance of HCG was 37.7 days, when the specific (beta-sub-HCG) assay was used. Recovery of pituitary function occurred within 4--9 days after abortion, as judged by increased plasma FSH concentrations. In fourteen of eighteen subjects a midcycle LH peak was observed which occurred between 16 and 29 days after abortion. Plasma oestradiol concentrations increased 2--16 days after the rise in plasma FSH. Considerable amounts of HCG still circulated in the blood but the preovulatory peak of oestradiol never began before HCG/LH concentrations had decreased to below the range of the mid-cycle LH peak.