Objective Small-for-gestational age infants are at an increased risk for disabilities and chronic health problems. Smoking and hypertension during pregnancy pose significant risks for fetal growth restriction. The study aims to identify whether (1) the timing of tobacco use modifies the risk of small-for-gestational age, (2) there are differences in association by percentile of small-for-gestational age (3rd, 5th, and 10th percentile), and (3) the effect of tobacco exposure on small-for-gestational age outcome is mediated by hypertension.
Materials and Methods Data were obtained from the 2009 Natality public use file available through the National Center for Health Statistics. Women were categorized into 11 groups depending on the trimester of tobacco exposure, the number of daily cigarettes smoked, and presence of hypertension. Multivariable log-linear regression models were performed to determine the association between percentile of singleton small-for-gestational age outcome (3rd, 5th, and 10th), trimester and degree of tobacco exposure, and hypertension.
Results Hypertension and smoking worked synergistically to restrict fetal growth. Hypertensive women who smoked heavily in all three trimesters were 4.34 times more likely to give birth to a 3rd percentile small-for-gestational age infant compared with nonsmoking normotensive women.
Conclusion The timing and duration of tobacco exposure mediates the risk and severity of fetal growth restriction.