PREVIOUS USE OF ORAL-CONTRACEPTIVES AND SPONTANEOUS-ABORTION

This analysis tests the hypothesis that women who conceive within 3 months after stopping oral contraceptives (''the pill'') have an intrinsically lower risk of chromosomally normal loss. About 30% of women show evidence of endocrine dysfunction, including anovulation, for 1-3 months after stopping the pill. In women who recover rapidly, and therefore are at risk of pregnancy, a common endocrinologic factor may account for both the quick return to normal functioning and improved intrauterine survival of the chromosomally normal conceptus. The hypothesis was tested in women with chromosomally normal (N = 334) and chromosomally aber rant (N = 239) spontaneous abortions. Women were classified according to the number of months between last pill use and last menstrual period. The adjusted odds ratios relating conception in months 0 and 1 after stopping the pill to chromosomally normal (vs chromosomally aberrant) loss were each 0.4, with upper 95% confidence limits of 1.0 and 0.9, respectively. The odds ratios for conception at longer intervals after stopping were 1.1 [95% confidence interval (CI) = 0.4-3.1], 0.7 (95% CI = 0.3-1.2), and 0.9 (95% CI = 0.5-1.5) for 2, 3-11, and greater than or equal to 12 months, respectively. Rates of spontaneous abortion in previous pregnancies were lowest in women who conceived quickly after stopping the pill. Further support: for an endocrinologic explanation requires direct measures of endocrine functioning in the post-pill period among women with varying reproductive histories.