Birth season associates with multiple anthropometric traits in Estonian children

Seasonal variation in maternal exposure to sunlight during pregnancy, which leads to a variation in vitamin D availability for a fetus, is a prevalent explanation for the variation of offspring traits with birth season. However, little consensus exists about the pregnancy period during which the fetus is most sensitive to maternal UV exposure and which offspring traits are most sensitive. We examined the association between 11 anthropometric traits and birth season/month among 18,459–23,876 Estonian children born in 1937–62. Nine traits showed seasonal patterns, which were generally weak, compared to the effects of family socioeconomic position (SEP). Clear nonlinear associations between offspring traits and birth month emerged only among children of mothers in non-manual professions. A possible explanation is that the growth of children in high-SEP families is more strongly buffered against any external exposures than the growth of children in low-SEP settings. For most traits, children born in spring/summer were larger than those born in autumn/winter. Hip width, trunk length and weight showed the most distinct seasonal patterns.孕期母体日光暴露的季节差异会导致胎儿维生素D供给量出现波动，这是解释子代性状随出生季节变化的主流假说。然而，学界对于胎儿对母体紫外线暴露最为敏感的孕期阶段，以及哪些子代性状最易受此影响，尚未达成广泛共识。本研究针对1937至1962年间出生的18459至23876名爱沙尼亚儿童，分析了11项人体测量学性状与出生季节/月份之间的关联。与家庭社会经济地位（socioeconomic position, SEP）的影响相比，9项性状呈现出季节性变化模式，但整体效应较弱。仅在母亲从事非体力职业的儿童群体中，子代性状与出生月份之间才呈现出显著的非线性关联。一种可能的解释是，相较于低社会经济地位家庭的儿童，高社会经济地位家庭的儿童生长发育更能抵御各类外界暴露因素的影响。对于多数性状而言，春夏季出生的儿童体型大于秋冬季出生的儿童。髋宽、躯干长度与体重的季节性变化模式最为显著。