BACKGROUND Nitrate is a widespread groundwater contaminant and a leading cause of drinking water quality violations in California. Associations between nitrate exposure and select adverse birth outcomes have been suggested, but few studies have examined gestational exposures to nitrate and risk of preterm birth (before 37 wk gestation). OBJECTIVE We investigated the association between elevated nitrate in drinking water and spontaneous preterm birth through a within-mother retrospective cohort study of births in California. METHODS We acquired over 6 million birth certificate records linked with Office of Statewide Health Planning and Development hospital discharge data for California births from 2000-2011. We used public water system monitoring records to estimate nitrate concentrations in drinking water for each woman's residence during gestation. After exclusions, we constructed a sample of 1,443,318 consecutive sibling births in order to conduct a within-mother analysis. We used separate conditional logistic regression models to estimate the odds of preterm birth at 20-31 and 32-36 wk, respectively, among women whose nitrate exposure changed between consecutive pregnancies. RESULTS Spontaneous preterm birth at 20-31 wk was increased in association with tap water nitrate concentrations during pregnancy of 5 to <10mg/L [odds ratio (OR)=1.47; 95% confidence interval (CI): 1.29, 1.67] and ≥10mg/L (OR=2.52; 95% CI: 1.49, 4.26) compared with <5mg/L (as nitrogen). Corresponding estimates for spontaneous preterm birth at 32-36 wk were positive but close to the null for 5 to <10mg/L nitrate (OR=1.08; 95% CI: 1.02, 1.15) and for ≥10mg/L nitrate (OR=1.05; 95% CI: 0.85, 1.31) vs. <5mg/L nitrate. Our findings were similar in several secondary and sensitivity analyses, including in a conventional individual-level design. DISCUSSION The results suggest that nitrate in drinking water is associated with increased odds of spontaneous preterm birth. Notably, we estimated modestly increased odds associated with tap water nitrate concentrations of 5 to <10mg/L (below the federal drinking water standard of 10mg/L) relative to <5mg/L. https://doi.org/10.1289/EHP8205.

中文翻译：

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妊娠和自然早产期间饮用水中的硝酸盐：加利福尼亚州母亲内部的回顾性分析。

背景技术硝酸盐是广泛的地下水污染物，并且是加利福尼亚州违反饮用水水质的主要原因。有人建议将硝酸盐暴露与某些不良的出生结局联系起来，但是很少有研究检查妊娠期硝酸盐暴露和早产风险（37周妊娠之前）。目的我们通过一项针对加利福尼亚出生的母亲内部回顾性队列研究，研究了饮用水中硝酸盐含量升高与自发性早产之间的关系。方法我们获得了超过600万份出生证明记录，这些记录与2000年至2011年加利福尼亚州出生的州卫生计划与发展办公室医院出院数据相关。我们使用公共水系统监测记录来估算每个女性的饮用水中的硝酸盐浓度 妊娠期间的住所。排除后，我们构建了一个1,443,318个连续兄弟姐妹出生的样本，以进行母亲内部分析。我们使用单独的条件逻辑回归模型来估计连续两次怀孕之间硝酸盐暴露发生变化的女性早产的机率分别为20-31周和32-36周。结果怀孕期间自来水硝酸盐浓度在5至<10mg / L时，自发早产在20-31 wk时增加[比值比（OR）= 1.47；95％置信区间（CI）：1.29、1.67]和≥10mg/ L（OR = 2.52； 95％CI：1.49、4.26），而<5mg / L（以氮计）。每周32-36周自然早产的相应估计为阳性，但对于5至<10mg / L硝酸盐（OR = 1.08; 95％CI：1.02，1.15）和≥10mg/ L硝酸盐（OR = 1.05）接近零值; 95％CI：0.85，1.31）vs. <5mg / L硝酸盐 我们的发现在一些二级和敏感性分析中都相似，包括在常规的个人设计中。讨论结果表明，饮用水中的硝酸盐与自发早产几率增加有关。值得注意的是，相对于<5mg / L，我们估计与5至<10mg / L（低于联邦饮用水标准10mg / L）的自来水硝酸盐浓度相关的几率会适度增加。https://doi.org/10.1289/EHP8205。我们估计相对于<5mg / L，自来水硝酸盐浓度为5至<10mg / L（低于联邦饮用水标准10mg / L）时，适度增加的几率。https://doi.org/10.1289/EHP8205。我们估计相对于<5mg / L，自来水硝酸盐浓度为5至<10mg / L（低于联邦饮用水标准10mg / L）时，适度增加的几率。https://doi.org/10.1289/EHP8205。