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Objective : although numerous studies have reported the association between birth season and sex ratio, few studies have been conducted in subtropical regions in a non-Western setting. The present study assessed the effects of pregnancy season on birth sex ratio in China. Methods : We conducted a national population-based retrospective study from — with children-parents pairs enrolled in the Northeast regions of China. Demographics and data relating to pregnancy and birth were collected and analyzed.
Results : After adjusting for parental age cut-off point was 30 years , region, nationality, mother education level, and mother miscarriage history, there is a significant statistical different mother pregnancy season on birth-sex. The birth-sex ratio varied with months.
Conclusions : Our results suggested that mothers pregnant in summer and winter were more likely to deliver girls, compared with those pregnant in spring. Pregnancy season may play an important role in the birth-sex.
Birth season has been associated with many human diseases [ 1 ] including cancer [ 2 ], or physiological activities e. Data from mammals showed that natural factors could affect the birth-sex through the parental condition [ 5 ]. Birth-sex ratios of humans have been reported to be affected by climate-related risks, such as temperature [ 6 ], although the chromosomes determine the sex.
The few studies that have examined the hypothesis that birth season and birth-sex are related have reported discrepant results, but have varied widely in design, analytical methods, age ranges and populations. For example, Rajani et al. Limited by being a hospital-based study design without considering the potential confounders, these findings cannot withstand scrutiny. Using monthly data of —, Melnikov et al. However, pregnancy season should be more essentially associated with birth-sex, although pregnancy season is associated with birth season.