346 - Pre-Pregnancy Body Mass Index and Smoking during Pregnancy: Differential Effects on Perinatal Outcomes

Publication Number: 346.6486

Sumera Aziz, University of Alberta Faculty of Medicine and Dentistry, Edmonton, AB, Canada; sarka Lisonkova, UBC, Vancouver, BC, Canada; YE SHEN, BC Children's Hospital Research Institute, Richmond, BC, Canada; Jeffrey N.. Bone, BC Children's Hosiptal Research Institute, Vancouver, BC, Canada; Lindsay Richter, University of British Columbia, Vancouver, BC, Canada; Joseph Ting, University of Alberta, Edmonton, AB, Canada

Background: Pre-pregnancy body mass index (BMI) and smoking are each linked to adverse perinatal outcomes. However, modifying effect of maternal smoking on pre-pregnancy BMI related perinatal outcomes remains underexplored.

Objective: We examined whether the associations between pre-pregnancy BMI and perinatal outcomes vary by smoking during pregnancy.

Design/Methods: A retrospective cohort study of singleton live births from 2004-2012 was conducted using data from the British Columbia Perinatal Data Registry extracted by Population Data BC (PopData BC). Pre-pregnancy BMI and smoking during pregnancy were self-reported. Pre-pregnancy BMI was categorized into underweight (BMI < 18.5 kg/m2), normal weight (18.5- 24.9 kg/m2), overweight (BMI: 25 to 29.9 kg/m2), and obese (BMI ≥30kg/m2). Perinatal outcomes included low birth weight (LBW, < 1500g), preterm birth (PTB, < 37 weeks gestation), small for gestational age (SGA, weight < 10th percentile for gestational age), and any congenital anomalies. Poisson regression with robust standard errors were used to estimate adjusted risk ratios (ARR) with 95% confidence intervals (CIs), adjusting for potential confounders, including maternal age, parity, region of residence, hypertension, diabetes, and prior history of any the following: LBW, neonatal death, stillbirth, or PTB.

Results: Overall, 568,239 women were included; 32,434 (5.71%) were underweight, 336,281 (59.2%) had normal BMI (reference), 121,965 (21.5%) were overweight, 77,559 (13.6%) were obese; and 6.95% were smokers (Table 1). Underweight women are at increased risk of delivering LBW and SGA babies, compared to those with normal BMI (Table 2). Both underweight and overweight women were associated with increased risks of PTB (Tables 2 & 3). Smoking modified the effect of BMI on PTB. In non-smokers, we found a U-shaped relationship between pre-pregnancy BMI and PTB (Table 3) with ARRs of 1.16 (95% CI: 1.11, 1.20) for underweight, 1.04 (95% CI: 1.02, 1.06) for overweight, and 1.08 (95% CI: 1.05, 1.11) for obese vs. women with normal BMI (Table 3). Among smokers, risk of PTB was lower in overweight and obese women (Table 3). Smoking did not increase the risk of LBW and SGA across BMI categories.

Conclusion(s): The risk of PTB increased when BMI deviated from normal and for underweight women, magnitude of the risk increased by maternal smoking. Counselling women, especially those with a low pre-pregnancy BMI, to avoid smoking during pregnancy is crucial for minimizing PTB risk.

CV_Sumera_Aziz.pdf

Perinatal outcome rates among women with singleton births by pre-pregnancy BMI, stratified by smoking during pregnancy


Strata-specific crude and adjusted risk ratios (ARRs) and 95% CIs for the relationship between pre-pregnancy BMI and perinatal outcomes