The nitrate never crossed the legal line. The preterm gap stayed under it.
Every sample in this study was compliant. That was the design.
Semprini linked 1983-88 Iowa finished-water nitrate to 113,328 births (medRxiv 10.64898/2026.09.14.26363048; preprint, not peer reviewed). Pregnancies with any first-trimester reading at or above the 10 mg/L federal limit were cut. What stayed: averages of 5 to under 10 mg/L, every drop legal, and more preterm birth: +1.04 percentage points, and +0.53 on very preterm. Both held after multiple-test correction.
The paper posts its whole pipeline, so I pulled the archived dataset and rebuilt the primary model. My sample: 113,331 rows against their 113,328. My estimates: +1.04 pp (95% CI 0.24 to 1.83) and +0.53 pp (0.08 to 0.97). Same numbers.
One in five of those births sat in the 5 to 10 band. The limit itself guards infants under six months from blue-baby syndrome (EPA). The first trimester was never its question.
What breaks: county-quarter average exposure, one state, 1980s data, observational. It's also a corrected redo of a 2025 study the author says was retracted; this version posts every step, and I checked the last one.
Checked at data level. Desk: one claim, traced to its source. [email protected]