Twinning rates in Chennai, India - A cross-sectional study

The city of Chennai is one of the largest metropolitan cities in India where apart from a large traditional population, there has been a continuous migration from rural areas and growing sophistication in lifestyle. Twinning rates trend in the present world would be interesting to study.

The aim of the present study was to analyse the twinning rate in the city of Chennai, the distribution amongst various city zones and the present trends in the co-relation between the maternal age of the twins with the zygosity.

A population-based study was conducted on twin births in various corporation Zones in the Chennai Metropolitan, between 2010 and 2012. As per the Chennai corporation and Health Department register, there were a total of 2,32,884 births registered in the city of which 4,500 were twin births over the 3 years. Only 1371 pairs were found residing in Chennai at the time of study, and hence, a study was conducted on this population only.

The data were analysed with Epiinfo software.

A twining rate of 19.3 per 1000 births was observed as per Corporation records. In the present study, the sample of 150 pairs, 34 pairs (22.6%) comprised of monozygotic (MZ) twins and 116 pairs (77.3%) comprised of dizygotic twins giving a ratio of 1:3. The maternal age groups 25-30 and 30-35 years comprised of the maximum twinning rates. Most twin births were of the first order. An analysis of Weinberg's Differential Rule method to determine zygosity showed a significant difference compared to the Questionnaire method.

The twinning rate observed in Chennai in the present study is interestingly very high, compared to the overall twinning rate reported in the past in the state of Tamilnadu. The Wienberg's Differential method for zygosity determination is again found to be questionable. The zygosity proportion, maternal age and parity relations are not very different from previously available data.