PREVIOUS USE OF ORAL-CONTRACEPTIVES AND SPONTANEOUS-ABORTION

This analysis tests the hypothesis that women who conceive within 3 mo nths after stopping oral contraceptives (''the pill'') have an intrins ically lower risk of chromosomally normal loss. About 30% of women sho w evidence of endocrine dysfunction, including anovulation, for 1-3 mo nths after stopping the pill. In women who recover rapidly, and theref ore are at risk of pregnancy, a common endocrinologic factor may accou nt for both the quick return to normal functioning and improved intrau terine survival of the chromosomally normal conceptus. The hypothesis was tested in women with chromosomally normal (N = 334) and chromosoma lly aber rant (N = 239) spontaneous abortions. Women were classified a ccording to the number of months between last pill use and last menstr ual period. The adjusted odds ratios relating conception in months 0 a nd 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 inter vals 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 g reater than or equal to 12 months, respectively. Rates of spontaneous abortion in previous pregnancies were lowest in women who conceived qu ickly after stopping the pill. Further support: for an endocrinologic explanation requires direct measures of endocrine functioning in the p ost-pill period among women with varying reproductive histories.