OBJECTIVE To investigate the relative contribution of genetic and environmental components to subfertility. DESIGN Twin design using a quantitative genetic liability threshold model that splits the variation of subfertility into additive genetic effects, common environmental effects, and unique environmental effects. SETTING Not applicable. PATIENTS A total of 9053 Danish monozygotic and dizygotic same-sex twins aged 18+ years from nationwide twin surveys (twins born 1931-1976). INTERVENTION Not applicable. MAIN OUTCOME MEASURES Time to pregnancy (TTP) restricted to first pregnancy as a binary outcome, with a cut-off point of 10 months. RESULTS Based on the Akaike information criterion, a model including additive genetic and unique environmental factors resulted in the best model fit. For females, the relative contribution of additive genetic factors to TTP was 28% (95% confidence interval [CI] 15%, 41%), whereas unique environmental factors explained 72% (95% CI 59%, 85%). For males, additive genetic factors explained 4% (95% CI 0%, 22%) of the variation in TTP, while unique environmental factors accounted for 96% (95% CI 78%, 100%). Results were overall similar for the crude model and consistent across surveys. CONCLUSION Unique environmental factors explain most of the observed variation in subfertility, when measured as waiting time to pregnancy.

中文翻译：

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丹麦双胞胎不育的遗传性

目的 调查遗传和环境因素对低生育力的相对贡献。设计 双胞胎设计使用定量遗传责任阈值模型，该模型将低生育力的变化分为加性遗传效应、共同环境效应和独特环境效应。设置 不适用。患者 来自全国双胞胎调查（出生于 1931-1976 年的双胞胎）共有 9053 名 18 岁以上的丹麦单卵和异卵同性双胞胎。干预 不适用。主要结局指标 妊娠时间 (TTP) 限于作为二元结局的首次妊娠，截止点为 10 个月。结果 基于 Akaike 信息准则，包括加性遗传和独特环境因素的模型产生了最佳模型拟合。对于女性来说，附加遗传因素对 TTP 的相对贡献为 28%（95% 置信区间 [CI] 15%, 41%），而独特的环境因素解释了 72%（95% CI 59%, 85%）。对于男性，附加遗传因素解释了 TTP 变异的 4% (95% CI 0%, 22%)，而独特的环境因素解释了 96% (95% CI 78%, 100%)。原始模型的结果总体相似，并且在调查中保持一致。结论 独特的环境因素解释了观察到的生育力低下的大部分变化，以等待怀孕的时间来衡量。原始模型的结果总体相似，并且在调查中保持一致。结论 独特的环境因素解释了观察到的生育力低下的大部分变化，以等待怀孕的时间来衡量。原始模型的结果总体相似，并且在调查中保持一致。结论 独特的环境因素解释了观察到的生育力低下的大部分变化，以等待怀孕的时间来衡量。