Birth order and its effects on childhood sleep quality: a large epidemiological study

Existing studies indicate that birth order may inherently link to children's sleep characteristics, however, the evidence is quite limited. This large epidemiological study was specially designed to quantify the association between birth order and sleep quality in children.

This cross-sectional study analyzed 16,936 children aged 3-12 years. Birth order was grouped as only child, firstborn, second-born, third-born, and fourth-born or later. Inverse probability of treatment weighting (IPTW) was applied to balance the demographic characteristics across groups. The association between birth order and sleep quality was examined by multivariable logistic regression.

Among the sampled children, 63.2 % were only children, 19.4 % firstborns, 15.7 % second-borns, 1.4 % third-borns, and 0.2 % fourth-or-later-borns. Second-or-later-born children had lower risk of poor sleep quality compared to firstborns across three sleep quality cut-offs (aOR ranged from 0.708 to 0.730 post-IPTW, all p < 0.05). When second-or-later-born children were subdivided into more categories, a pattern resembling a dose-response relationship was observed. Analyses across eight dimensions of sleep problems further supported these associations. Stronger associations were identified in males, preschool-aged children, those with insufficient sleep duration, those with family sleep disorder history, and those with higher socioeconomic status. Only children showed overall sleep quality comparable to firstborns, however, they were more susceptible to sleep problems in specific subscales.

Birth order may play an intrinsic regulating role in children's sleep quality. Second-or-later-born children demonstrated better sleep quality, which appeared stronger as birth order increased. Only children showed greater susceptibility to specific sleep problems. These findings highlight the importance of considering family structure when assessing children's sleep health.