Ease of conception in mothers of twins

A relationship between fecundability and dizygotic twinning is discussed. 2 kinds of data suggest an association between high fecundability and twinning. First twinning is elevated among conceptions occurring in the first 3 months. In 1 study it was shown that for conception that occurred in the first 3 months of marriage twins exceeded expectation by 19%. Secondly the twinning rate is higher in premarital and illegitimate conceptions. It is noted that highly fecundable women are more likely to be caught by pregnancy and if they are also twin-prone the twinning rate will be high among resulting births. There was a remarkable rate of twinning in 1946. The increase in twinning was most marked among women between the ages of 15 and 29 whose husbands were more likely to have been in service. By an improvised method of estimation average time to conception was estimated to be about 2.2 months shorter for mothers of twins. Prompt conception and twin proneness may both be expressions of 1 physiological characteristic. The long-term decline in dizygotic twinning in the United States could be explained by high fecundability in twin prone women. The increase in family planning has tended to eliminate any weighting by fecundability and would have brought twinning down toward the average rate for all women.