Does the use of oral contraception depress DZ twinning rates?

Data based on total births from a geographically defined population with zygosity determined from blood samples and placentation and with data on the use of oral contraceptives routinely collected in early pregnancy showed no association between oral contraceptive use prior to pregnancy in either MZ or DZ twinning. Three mutually exclusive control groups of singletons were used to take account of age, parity and secular trends.