Objective To establish the Shanghai twin birth cohort （STBC） and analyze the effects of genetic factors， shared environment， and non-shared environment interactions on birth health and growth and development of newborns.
Methods Based on the population-wide birth cohort in Shanghai， a comprehensive survey was conducted on the families with double and multiple babies born after January 1， 2015 to collect information on birth health， growth and development， and the family environment of the babies.
Results By December 31， 2021， a total of 7 195 pairs （14 405 cases） of twins were successfully included in the STBC survey. The average birth length of twins was 47.2 cm and average birth weight was 2 465.3 g. Heterozygous twins accounted for 69.05% and preterm babies accounted for 57.07%. The average age of the mothers of twins was 31.82 years， and the average age of the fathers was 33.87 years， with more than 80% of the parents having a college degree or above. 44.50% of the mothers used assisted reproductive technologies， 7.40% had illnesses during pregnancy， and 15.90% were exposed to passive smoking during pregnancy. During the survey period， the average monthly increase in the length of the twin infants was 2.09 cm， and the average monthly weight gain was 0.53 kg.
Conclusion The incidence of adverse outcomes such as maternal cesarean section rate， preterm birth， and low birth weight is higher in the twin birth population. Information on birth health as well as growth and development in childhood and adolescence in the twin birth population is collected based on STBC， which can provide a solid data foundation for studying children’s chronic non-communicable diseases， psychological and behavioral disorders and other complex health problems caused by the combined effects of genetics and the environment.
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