Prolonged exposure to nitrate in drinking water does not adversely impact prenatal or birth outcomes in a rat model

Nitrate (NO3−) is a common drinking water contaminant associated with increased risks of adverse pregnancy outcomes at concentrations below the World Health Organisation (WHO) drinking water guidelines (50 mg/L NO3−). However, causal evidence at relevant concentrations is sparse. This study aimed to characterise the effects of prolonged exposure to drinking water nitrate at concentrations relevant to human exposure on maternal, fetal, and birth outcomes. Wistar rats were exposed to 0, 50 or 100 mg/L NO3− as sodium nitrate in drinking water three weeks pre-conception and throughout gestation. At 21 days gestation, fetal and placental weights and morphology, maternal outcomes including plasma nitrate and nitrite, endocrine and inflammatory markers, and uterine artery haemodynamics were analysed. In a second cohort, birth timing and weight were assessed. While nitrate exposure substantially increased maternal plasma nitrate and nitrite concentrations, no consistent effects were seen on fetal or placental outcomes or endocrine/inflammatory markers. Several birth complications, small litters and higher uterine artery blood velocities were noted in nitrate-exposed groups, but these outcomes were highly variable. These results show that chronic exposure to nitrate at or above the WHO drinking water guidelines subtly impacts rat pregnancy and do not provide causal support for the findings of epidemiological studies.