Chromosome breakage studies in lymphocytes from normal women, pregnant women, and women taking oral contraceptives.

Cytogenetic studies of 977 lymphocyte cultures from ten normal men and 54 normal women have shown: (1) variations in the frequencies of chromosome breakages among consecutive cultures from the same person and among cultures from different people, indicating that many extraneous factors may affect lymphocyte chromosomes, and (2) significantly higher average breakages in cultures from nulligravidas taking oral contraceptives (OC) and in pregnant women who had had previous pregnancies than in nulligravidas who had never taken the pill. The increase in breakages in cultures from the OC users was not observed in all cultures and could not be correlated with length of time on pill or stage of the pill cycle, suggesting that synthetic hormones do not directly damage lymphocyte chromosomes. Since estrogens and progestogens are known to affect many metabolic and biochemical systems, it is possible that these substances may induce in OC users and pregnant women a slightly altered in vivo condition in which increased chromosome breakages may be expressed.