Maternal health
Is any prenatal smoking safe for preterm birth?
Open access · cc by · source: Europe PMC
Among 25.6 million US births, even 1–2 cigarettes/day in the first or second trimester raised preterm-birth odds; quitting before pregnancy matched nonsmoker risk.
How this study connects
Role on claims
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Even low-intensity maternal smoking raises preterm-birth odds; quitting before pregnancy looks like never-smoking risk.
US birth-certificate analyses showed first-trimester smoking of 1–2 to ≥20 cigarettes/day associated with ORs ~1.31–1.53 for preterm birth; low-intensity smoking in either trimester still increased risk, while quitting before pregnancy tracked with never-smoker risk.
Evidence for the claim as stated.
Active tobacco smoking maps onto many CVD subtypes, not only “heart disease” as one bucket.
Large cohort evidence linked tobacco smoking to risk across dozens of fatal and non-fatal cardiovascular disease subtypes.
Scope note — reproductive preterm endpoint ≠ adult CVD subtype incidence
Limits the claim's scope: a different population, assay, or outcome.
Maternal cigarette dose and preterm birth odds vs Conservative SHS relative-risk floors across outcomes vs Active smoking across CVD subtypes
Evidence for the claim as stated.
There is no clearly safe low level of smoking in pregnancy, and quitting before conceiving is what brings risk back to baseline.
In US birth records covering about 25 million mother-infant pairs, first-trimester smoking was linked to higher odds of preterm birth (odds ratios about 1.31 to 1.53 across intensities, even at 1-2 cigarettes a day); women who quit before pregnancy had risk similar to never-smokers, while quitting only after conception did not fully remove the excess.
Evidence for the claim as stated.
There is no clearly safe low level of smoking in pregnancy, and quitting before conceiving is what brings risk back to baseline.
In US birth records covering about 25 million mother-infant pairs, first-trimester smoking was linked to higher odds of preterm birth (odds ratios about 1.31 to 1.53 across intensities, even at 1-2 cigarettes a day); women who quit before pregnancy had risk similar to never-smokers, while quitting only after conception did not fully remove the excess.
Scope note — Observational birth-certificate data with self-reported smoking; associations, not proven causal effects.
Limits the claim's scope: a different population, assay, or outcome.
Maternal BMI clearly shifts hypertensive and delivery outcomes, but neither BMI cohort found a clear link with overall preterm birth: the Scottish study saw no difference in preterm birth before 37 weeks after adjustment (though more very preterm births in obese women), and the Australian composite of serious outcomes and preterm birth did not differ. Smoking, by contrast, is tied to preterm birth in the US data.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Maternal cigarette dose and preterm birth odds vs Conservative SHS relative-risk floors across outcomes vs Active smoking across CVD subtypes
Maternal BMI clearly shifts hypertensive and delivery outcomes, but neither BMI cohort found a clear link with overall preterm birth: the Scottish study saw no difference in preterm birth before 37 weeks after adjustment (though more very preterm births in obese women), and the Australian composite of serious outcomes and preterm birth did not differ. Smoking, by contrast, is tied to preterm birth in the US data.
Study at a glance
- Design
- Cohort — Maternal smoking before and during pregnancy vs preterm birth
- N
- Perinatal cohort; single analytic N not extracted
- Population
- Pregnant women with recorded smoking status before and during pregnancy
- Outcome
- Preterm-birth risk associated with maternal cigarette smoking
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Is any prenatal smoking safe for preterm birth?
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
25,623,479 women were included (mean age 29).
This study included 25,623,479 women, with a mean age of 29 years (range 20–50 years)
First-trimester 1–2 cigarettes/day OR 1.31 (1.29–1.33) vs nonsmokers.
1–2, 3–5, 6–9, 10–19, and ≥20 cigarettes per day during the first trimester compared with mothers who did not smoke were 1.31 (1.29–1.33), 1.31 (1.30–1.32), 1.33 (1.31–1.35), 1.44 (1.43–1.45), and 1.53 (1.52–1.55)
Key findings
First-trimester smoking of 1–2 up to ≥20 cigarettes/day had ORs from 1.31 to 1.53 vs nonsmokers. Low-intensity smoking in either trimester still increased risk. Quitting before pregnancy yielded risk comparable to never smokers; quitting only after conception did not fully normalize risk. Associations varied by age, race/ethnicity, and education.
Methodology
Analyzed NVSS singleton mother–infant pairs (2011–2018) with complete smoking and gestational-age data, estimating adjusted odds of preterm birth by smoking status and cigarettes/day before pregnancy and in the first/second trimester.
Limitations
Self-reported smoking on birth certificates can misclassify exposure; residual confounding and selection after excluding hypertension/diabetes limit causal claims about intervention effects.
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