The twinning rates and epidemiological characteristics of births in southeast Uttar Pradesh, India.

Birth statistics over a period of 5 years were analyzed to study epidemiological characteristics of twinning in Southeast Uttar Pradesh, India. The data revealed higher incidence of breech twins (11.84% of all cotwins) as compared to breech single births (2.18%). But the perinatal mortality and caesarean section rates were similar in both twin and singleton pregnancies. The cumulative twinning rate over the studied period was 11.70 per 1000 live births. The MZ and DZ twinning rates were estimated respectively as 3.67 and 8.03 per mill. The mean maternal age of sampled mothers was 26.42 years with one standard deviation of 5.30 years. The twinning rate for mothers over 35 years of age was about four times higher than that in mothers younger than 20 years. Incidentally, the twinning rate was the highest at parity four and a non-linear curve could more appropriately be fitted to the series of data. Seasonal variations were observed for both twin and singleton births. The highest frequency of births was observed from August through October. But seasonal index for twinning rate showed a clear bimodal distribution with peaks in April (223) and September (167).