The Wuhan Pre/Post-Natal Twin Birth Registry (WPTBR) is one of the largest twin birth registries with comprehensive medical information in China. It recruits women from the first trimester of pregnancy and their twins from birth. From January 2006 to May 2016, the total number of twins enrolled in WPTBR is 13,869 twin pairs (27,553 individuals). The WPTBR initiated the Wuhan Twin Birth Cohort (WTBC). The WTBC is a prospective cohort study carried out through incorporation of three samples. The first one comprises 6,920 twin pairs, and the second one, 6,949 twin pairs. Both are population-based samples linked to the WPTBR and include pre- and post-natal information from WPTBR. The second sample includes neonatal blood spots as well. Using a hospital-based approach, we recently developed a third sample with a target enrolment of 1,000 twin pairs and their mothers. These twins are invited, via their parents, to participate in a periodic health examination from the first trimester of pregnancy to 18 years. Biological samples are collected initially from the mother, including blood, urine, cord blood, cord, amniotic fluid, placenta, breast milk and meconium, and vaginal secretions, and later from the twins, including meconium, stool, urine, and blood. This article describes the design, recruitment, follow-up, data collection, and measures, as well as ongoing and planned analyses at the WTBC. The WTBC offers a unique opportunity to follow women from prenatal to postnatal, as well as follow-up of their twins. This cohort study will expand the understanding of genetic and environmental influences on pregnancy and twins' development in China.

Background Most studies of associations between parental support behaviours for physical activity (PA) and children’s moderate-to-vigorous physical activity (MVPA) have been conducted in developed countries, and they have focused on maternal or parental support behaviours. Children’s MVPA time (i.e., weekdays vs. weekends) has not been adequately differentiated. This paper investigated the associations of paternal and maternal support behaviours for PA with the proportion of children who met the MVPA recommendations on weekdays and weekends in China. Methods Cross-sectional data of 517 father–child dyads and 1422 mother–child dyads were analysed. The children recorded PA diaries on 7 consecutive days to assess their MVPA time. The father or mother completed a questionnaire concerning their support for children’s PA. Multivariate logistic regression was used to investigate the independent effects of paternal and maternal support behaviours for PA on whether children met the MVPA recommendations for weekdays, weekends, and the whole week. Results Significantly fewer children met the MVPA recommendations on weekends (37.8%) than on weekdays (62.8%). Higher paternal (odds ratio [OR] = 1.098, 95% confidence interval [CI]: 1.009–1.195) and maternal (OR = 1.076, 95% CI: 1.021–1.134) total support behaviour scores were associated with higher odds of children meeting the MVPA recommendations on weekends, after controlling for covariates. Paternal PA knowledge-sharing with the child was positively associated with children meeting the MVPA recommendations on weekends (OR = 1.319, 95% CI: 1.055–1.649); it tended to be associated with children meeting the MVPA recommendations on weekdays and throughout the week, although these associations were not statistically significant. Maternal reservation of PA time for the child was positively associated with a higher likelihood of children meeting the MVPA recommendations on weekdays (OR = 1.160, 95% CI: 1.025–1.313), weekends (OR = 1.241, 95% CI: 1.097–1.403), and throughout the week (OR = 1.214, 95% CI: 1.076–1.369). Conclusions Paternal and maternal support behaviours for PA should be enhanced on weekends to increase children’s MVPA. Fathers should share PA knowledge with children and mothers should reserve PA time for children every day.