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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怀孕和自然早产期间饮用水中的硝酸盐：加利福尼亚州的回顾性内部母亲分析。

背景硝酸盐是一种广泛存在的地下水污染物，并且是加利福尼亚州饮用水质量违规的主要原因。已经提出了硝酸盐暴露与特定不良分娩结果之间的关联，但很少有研究检查妊娠期硝酸盐暴露和早产风险（妊娠 37 周前）。目的 我们通过一项针对加利福尼亚分娩的母亲内部回顾性队列研究，调查了饮用水中硝酸盐含量升高与自发性早产之间的关联。方法 我们获取了超过 600 万份出生证明记录，这些记录与 2000 年至 2011 年加州出生的全州健康规划和发展办公室的出院数据相关联。我们使用公共供水系统监测记录来估计每位女性饮用水中的硝酸盐浓度 s 怀孕期间的住所。排除后，我们构建了一个包含 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分别估计了在连续怀孕期间硝酸盐暴露发生变化的女性在 20-31 周和 32-36 周时早产的几率。结果 妊娠期自来水硝酸盐浓度为 5 至 <10mg/L [优势比 (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）与 <5mg/L（以氮计）。对于 5 至 <10 毫克/升硝酸盐（OR=1.08；95% CI：1.02, 1.15）和≥10mg/L 硝酸盐（OR=1.05），32-36 周自发早产的相应估计值是阳性但接近零; 95% CI：0.85, 1.31) vs. <5mg/L 硝酸盐。我们的研究结果在几个二级和敏感性分析中是相似的，包括在传统的个人水平设计中。讨论 结果表明，饮用水中的硝酸盐与自然早产的几率增加有关。值得注意的是，我们估计自来水硝酸盐浓度从 5 到 <10mg/L（低于 10mg/L 的联邦饮用水标准）相对于 <5mg/L 的几率略有增加。https://doi.org/10.1289/EHP8205。我们估计自来水硝酸盐浓度为 5 至 <10mg/L（低于 10mg/L 的联邦饮用水标准）相对于 <5mg/L 的几率略有增加。https://doi.org/10.1289/EHP8205。我们估计自来水硝酸盐浓度为 5 至 <10mg/L（低于 10mg/L 的联邦饮用水标准）相对于 <5mg/L 的几率略有增加。https://doi.org/10.1289/EHP8205。