Abstract: Background: Excessive salt intake has been strongly associated with multiple health conditions, while evidence linking salt consumption during pregnancy and birth outcomes remains limited. We aimed to investigate the association between salt intake during pregnancy and adverse outcomes of birth weight. Methods: Our study was based on a prospective cohort study that has followed 4267 mother–child pairs since 2017 in Shanghai, China. Salt consumption was estimated based on the cooking salt and soy sauce from household condiments consumed, weighing measurements over a week, and then categorized into <5.0 (reference), 5.0–10.0, and ≥10.0 g/day. Salt density was calculated as the amount of salt divided by the total energy intake from food frequency questionnaires. Outcomes related to birth weight were defined according to standard clinical cutoffs, including low birth weight (LBW), macrosomia, small for gestational age (SGA), and large for gestational age (LGA). Results: Multivariable-adjusted odds ratios (ORs) of LBW were 1.72 (95% CI 1.01–2.91) for 5.0–10.0 g/day salt intake, and 2.06 (95% CI 1.02–4.13) for ≥10.0 g/day, compared to those of <5.0 g/day (p-trend = 0.04). For SGA, ORs were 1.46 (95% CI 1.09–1.97) for 5.0–10.0 g/day and 1.69 (95% CI 1.16–2.47; p-trend = 0.006) for ≥10.0 g/day. Similarly, the OR comparing the extreme tertile (high vs. low) of salt density was 1.91 (95% CI 1.08–3.36; p-trend = 0.01) for LBW and 1.63 (95% CI 1.18–2.25; p-trend < 0.001) for SGA. No significant associations were observed for salt intake in relation to macrosomia or LGA. These findings remain stable in all sensitivity and subgroup analyses. Conclusions: In this study, habitual cooking salt intake above 5 g/day was associated with increased risks of LBW and SGA, which warrants confirmation by interventional studies.
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