Secular changes in twinning rates in England and Wales.
The monozygotic twinning rate in England and Wales seems to have increased over the years of 1957-1977. This constitutes evidence against the suggestion that the secular decline in dizygotic twinning rates over the same period has been due to an increase in spontaneous abortion rates.
D001723:Birth Rate; D004739:England; D005260:Female; D006801:Humans; D011247:Pregnancy; D013997:Time Factors; D014427:Twins; D014852:Wales