We conducted a case-control study of factors that may be related to the prevalence of multiple births with at least one liveborn. Over a period of 15 months during 1991–1992 in Athens, Greece, we identified 380 women who had a multiple birth that was delivered in one of the six larger maternity hospitals in the area. We selected as controls 380 livebirth singleton pregnancies delivered at the same hospitals immediately following a multiple pregnancy. All mothers were interviewed in the maternity wards or at home, and zygosity w’as ascertained through the similarity method. The odds ratio for ovulation-inducing drugs was not elevated for monozygotic twins, but it was 9-fold for dizygotic twins and 90-fold for triplets or quadruplets. We excluded drug-induced pregnancies, twins of indeterminable zygosity, and all triplets from further analyses. We found no remarkable association between any of the study variables and the occurrence of monozygotic twins, with the exception of an increasing trend with age. For dizygotic twins, we found weak associations in the expected directions with maternal age (positive) and height (positive) as well as with parity and number of induced abortions (positive). A history of oral contraceptive use was inversely, but weakly, associated with dizygotic twinning. Each cup of coffee per day was associated with an increment in the odds ratio of 1.23-fold (95% confidence interval = 1.05–1.43). Restriction of the analysis to dizygotic twins of different gender increased the point estimate of the odds ratio to 1.31 for each cup of coffee consumed daily. There was no association of tobacco smoking with dizygotic twinning, after controlling for coffee intake.
|Number of pages||5|
|Publication status||Published - 1995|
- Multiple pregnancies
- Oral contraceptives
- Risk factors