Mothers in the United States who smoke are more likely to deliver smaller babies even after a full-term pregnancy, increasing the risks of birth defects and neurological disorders later in life, say researchers from McGill University and the University of Toronto in Canada.
Their study was published in the Journal of Perinatal Medicine. The following story is from McGill University and was published on 20 September 2021.
The team of researchers, which includes Assistant Professor Michael Dahan and Dr Ido Feferkorn of the McGill University Health Care Centre, examined the effects of smoking on more than nine million deliveries in the Unites States over 11 years, one of the largest studies to date. This is a Q&A with Dahan and Feferkorn.
What question did you set out to answer?
Smoking is one of the most important modifiable risks factors for health.
Although smoking during pregnancy is thought to increase the risk of a wide range of problems, most studies to date have been relatively small – looking at just around 5,000 smokers in most cases.
Our study examined the delivery outcomes in 443,590 smokers and 8,653,198 non-smokers. We set out to study the effects of smoking in a large population, putting the findings of the smaller studies to the test.
What did you find?
We found that mothers who smoke had a 40% increased risk of premature birth and 50% increased risk of rupturing the amniotic sac surrounding the foetus before labour begins. More substantially, there was a 130% increased risk of having a baby that was too small for its developmental stage.
Our findings confirmed the effects detected in other smaller studies. Surprisingly, we also discovered that smoking mildly decreased certain pregnancy risks including developing preeclampsia, which can lead to infections in the uterus and bleeding and require delivery by caesarean section.
We believe that the smaller infant size induced by smoking may contribute to less bleeding and less need for caesarean sections.
What advice would you give?
The fact that smoking decreases some pregnancy risks does not mean pregnant women should start smoking.
There are very substantial risks with delivering a small baby, which can have serious consequences on the long-term health of the infant. Babies with low birth weight often have increased rates of diabetes, heart disease, kidney failure, and even certain cancers later in life.
In childhood, infants that are born too small are at increased risk of intestinal and urinary disorders, lung problems, and adverse neurological outcomes. Mothers who smoke can reduce these risks by quitting.
The relation between cigarette smoking with delivery outcomes. An evaluation of a database of more than nine million deliveries
Ido Feferkorn, Ahmad Badeghiesh, Haitham Baghlaf and Michael H Dahan
Author affiliations: McGill University and University of Toronto in Canada.
Published in the Journal of Perinatal Medicine on 30 July 2021.
Abstract
Objectives
Smoking in pregnancy is associated with an increased risk of preterm birth (PTB), intrauterine growth restriction, placental abruption and perinatal death.
The association between smoking and other delivery outcomes, such as chorioamnionitis, mode of delivery or post-partum haemorrhage (PPH), however, is insufficient as only few studies addressed these issues.
The aim of the study was to evaluate the association between prenatal smoking and delivery outcomes in a large database, while controlling for confounding effects.
Methods
A retrospective population-based study using data from the Healthcare Cost and Utilisation Project-Nationwide Inpatient Sample (HCUP‐NIS). A dataset of all deliveries between 2004 and 2014 (inclusively) was created. Our control group included all pregnant women who did not smoke during pregnancy, which was compared to pregnant women who smoked.
A multivariate logistic analysis was conducted, adjusting for any statistically significant confounding effects.
Results
Our study identified 9,096,788 births between 2004 and 2014. Of which 443,590 (4.8%) had a documented diagnosis of smoking.
A significantly higher risk was found for PTB (odds ratio 1.39, CI 1.35–1.43), preterm premature rupture of membranes (odds ratio 1.52, CI 1.43–1.62) and small for gestational age (SGA) neonates (odds ratio 2.27, CI 2.19–2.35).
The risks of preeclampsia (odds ratio 0.82, CI 0.78–0.85), chorioamnionitis (odds ratio 0.88, CI 0.83–0.4), PPH (odds ratio 0.94 CI 0.9–0.98) and operative vaginal delivery (odds ratio 0.9, CI 0.87–0.94) were lower among smokers.
Conclusions
This large database confirms the findings of previous smaller studies, according to which smoking decreases the risk of preeclampsia while increasing the risk of PTB and SGA neonates.
The current study also revealed a decreased risk for PPH as well as for chorioamnionitis among pregnant smokers.
McGill University material – Dangers of smoking during pregnancy (Open access)
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Just a cigarette a day in pregnancy doubles Sudden Infant Death risk
Nicotine’s effect on the developing embryo studied in new model