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Smoking, preterm birth synergistically increase maternal CVD risk
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An additive and dose-dependent interaction between maternal smoking and preterm birth increases the maternal risk for CVD, according to recent findings.
“Our research shows for the first time that smoking and preterm birth interact to create a greater CVD risk than either risk factor on its own,” Anh D. Ngo, research fellow at the University of Sydney at Royal North Shore Hospital in New South Wales, Australia, said in a press release.
Ngo and colleagues assessed the association between smoking and preterm birth in 902,008 women from New South Wales who gave birth to single infants between 1994 and 2011, over a median follow-up of 7.3 years. The primary outcome was CVD-related hospitalization or death more than 42 days after delivery. The researchers controlled for pregestational diabetes, gestational diabetes, hypertension, fetal death, infants small for gestational age and maternal age.
According to the results, 8.5% (n = 76,204) of women had a preterm birth, 19% (n = 171,370) smoked while pregnant and 2.4% (n = 21,442) met both conditions. Nearly 5,000 CVD-related events were reported, including 36 deaths and 4,930 hospitalizations for CHD (n = 2,462), MI (n = 929), cerebrovascular events (n = 2,211) or congestive HF (n = 582).
The incidence rate for first CVD event was 67 per 100,000 person-years at risk. Among women who experienced an event, the median age at the time of last delivery was 35 years, and the median age at the time of their first CVD event was 42 years.
Compared with nonsmokers who gave birth at full term, the risk for CVD tripled among smokers with preterm births (HR = 3.35; 95% CI, 2.96-3.8) and was greater in these participants than in those with only one condition (smokers with term births, HR = 2.1; 95% CI, 1.96-2.24; nonsmokers with preterm births, HR = 1.73; 95% CI, 1.55-1.93). The sum of risks in participants with both conditions demonstrated a significant additive interaction between smoking and preterm births (synergy index = 1.29; 95% CI, 1.05-1.58).
The risk for CVD was stronger among smokers with an extreme preterm birth (20 to 33 weeks gestation; HR = 3.83; 95% CI, 3.23-4.69) compared with a moderately preterm birth (34-36 weeks gestation; HR = 3.18; 95% CI, 2.76-3.66) and in smokers with two or more preterm births (HR = 4.47; 95% CI, 3.39-5.88) compared with one preterm birth (HR = 3.2; 95% CI, 2.81-3.64).
The results were similar for CHD, MI, cerebrovascular and congestive HF events when assessed individually. The researchers wrote that participants’ absolute risks would be more evident later in life when CVD plays a greater role in morbidity and premature death.
“Our findings have numerous implications for CVD protection,” Ngo said in the release. “Doctors should take into account the joint effects of smoking and preterm birth when assessing a woman’s CVD risk. Doctors should also consider the need for preventive therapy to timely control for biological disorders preceding CVD such as hypertension and dyslipidemia when these occur.” – by Stephanie Viguers
Disclosure: The researchers report no relevant financial disclosures.
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