The authors earlier conducted a retrospective study of time to pregnancy among a group of pregnant women in Minnesota, in order to investigate the relation between cigarette smoking and fecundability. Further analysis of these data shows that women who had been exposed as children to cigarette smokers had increased fertility. This finding lacks biologic plausibility. However, the authors found a similar association in a group of North Carolina women whose fecundability had been measured prospectively. Furthermore, both groups showed an apparent dose-response effect. The authors briefly describe this unexpected finding so that it might be more fully explored in other studies.
PIP: A retrospective study of pregnant women in Minnesota and a prospective study of North Carolina women revealed an apparent increase in fecundability among women exposed passively to cigarette smoke in childhood. In 1983, 678 Minnesota women with planned pregnancies were interviewed by telephone regarding the number of cycles it had taken them to become pregnant. These data were used to estimate the women s fecundability of per-cycle probability of conception. 663 of these women were reinterviewed a year later to collect data on their prenatal and childhood exposure to cigarette smoking. Results are presented on 631 women. When women who were exposed to their mothers' smoking during pregnancy were compared with women who were not exposed, both sets of women took an average of 3.4 cycles to become pregnant, i.e., there was no overall effect of prenatal exposure on fecundability. There was a relation between women's fecundability and their exposure as children to adults who smoked. Exposed women had fewer numbers of cycles to pregnancy, indicating higher fecundability. Women with no exposure took 3.8 cycles to become pregnant; those with exposure to 1 smoker took 3.4 cycles and those with exposure to 2 or more cycles took 3.1 cycles. The model also allowed for the consideration of possible confounding effects of other factors associated with fecundability: recent pregnancy or nursing, frequency of intercourse, recent oral contraceptive use, and the smoking habits of the woman herself. The association of smoke exposure during childhood with higher fecundability persisted as each variable was added to the model. The results were compared with similar data collected from a prospective study in North Carolina (1983-85). In the Minnesota study, a woman's prenatal exposure to her mother's smoking was weakly associated with decreased fecundability, whole her exposure to smokers during childhood was more strongly associated with higher fecundability. These 2 trends were present in the North Carolina study, but the association with prenatal exposure was the stronger.