Population attributable risks for low birth weight among singleton births—Colorado, Ashley Juhl, MSPH Epidemiology, Planning and Evaluation Branch Prevention Services Division Colorado Department of Public Health and Environment CSTE June 14, 2011

Outline Background on low birth weight Purpose of this analysis Methods for this analysis Results of the analysis Discussion of analysis results Recommendations based on the results

Background and Purpose

Background 2009 low birth weight rate in Colorado = 8.8% Preliminary 2009 low birth weight rate for the United States = 8.2% Low birth weight outcomes – Neonatal mortality and morbidity – Long-term developmental and neurological disabilities and complications

Background Known risk factors for low birth weight – Maternal smoking – Maternal alcohol consumption – Maternal age (<15 years and 35+ years) – Weight gain below the recommended range based on prepregnancy BMI category (inadequate weight gain) – Previous preterm birth – Social and economic factors (low income, low educational level, stress, unmarried, domestic violence or abuse) – Infections and placental problems

Previous Colorado Study Population attributable risk analysis among singleton births Inadequate weight gain during pregnancy (1 in 8 low weight births) Smoking during pregnancy (1 in 8 low weight births) Inadequate weight gain and/or smoking (1 in 3 low weight births)

Purpose To determine if the same risk factors still contribute to low birth weight among singletons

Methods

Colorado birth certificates – Cross-sectional study of a birth cohort – Live births to Colorado residents – Singletons only (N=202,498)

Variables Outcome of interest – Low birth weight <2,500 grams (5 lbs, 8 oz or less)

Variables Risk factors – Inadequate maternal weight gain Based on 1990 IOM recommendations – Smoking during pregnancy – Premature rupture of the membranes – Pregnancy induced hypertension or eclampsia – Abruptio placenta – Short interpregnancy interval (<12 months between previous delivery and subsequent conception) – No prenatal care – Placenta previa – Altitude > 10,000 feet (maternal residence at birth)

Variables (continued) Combined risk factor – Mothers gain inadequately OR mothers smoke OR mothers gain inadequately and smoke

Analysis Steps Step 1. Calculated the prevalence of each risk factor in the population Step 2. Calculated low birth weight rate for each risk factor Step 3. Calculated relative risks (RR) and 95% confidence intervals for each risk factor Step 4. Calculated population attributable risk (PAR) percent and 95% confidence intervals for each risk factor

Results

Maternal Characteristics Colorado Singleton Births Age (years) Mothers (%) N=202,498 <186,499 (3.2) ,907 (6.4) ,456 (22.9) ,516 (27.9) ,695 (24.0) 35+31,408 (15.5)

Maternal Characteristics Colorado Singleton Births Race/Ethnicity Mothers (%) N=202,498 White, non Hispanic119,210 (58.9) White, Hispanic55,949 (27.6) Black9,680 (4.8) Asian American/Pacific Islander7,124 (3.5) American Indian/Native Alaskan2,061 (1.0)

Step 1. Prevalence Colorado Singleton Births Risk FactorPrevalence Inadequate weight gain and/or smoking26.2% Inadequate weight gain during pregnancy18.7% Short interpregnancy interval16.2% Smoking during pregnancy8.7% Pregnancy induced hypertension or eclampsia3.5% Premature rupture of the membranes2.5% No prenatal care1.5% Abruptio placenta, placenta previa, and altitude >10,000 feet each had prevalence below 1%.

Step 2. Low Birth Weight (LBW) Rate Colorado Singleton Births Risk FactorLBW Rate Premature rupture of the membranes36.9% No prenatal care21.0% Pregnancy induced hypertension or eclampsia20.6% Smoking during pregnancy12.2% Inadequate weight gain during pregnancy10.5% Inadequate weight gain and/or smoking10.4% Short interpregnancy interval6.9% Colorado singleton low birth weight rate = 7.0%

Step 3. Relative Risks (RR) for Low Birth Weight Colorado Singleton Births Risk FactorRR (95% CI) Premature rupture of the membranes5.91 ( ) No prenatal care3.26 ( ) Pregnancy induced hypertension or eclampsia 3.14 ( ) Inadequate weight gain and/or smoking1.91 ( ) Smoking during pregnancy1.87 ( ) Inadequate weight gain during pregnancy1.79 ( ) Short interpregnancy interval1.15 ( )

Step 4. Population Attributable Risks (PAR) for Low Birth Weight Colorado Singleton Births Risk FactorPAR (95% CI) Inadequate weight gain and/or smoking19.4% ( ) Inadequate weight gain during pregnancy12.9% ( ) Premature rupture of the membranes11.1% ( ) Smoking during pregnancy7.1% ( ) Pregnancy induced hypertension or eclampsia 6.9% ( ) No prenatal care4.2% ( ) Short interpregnancy interval2.4% ( )

Discussion and Recommendations

Discussion Inadequate maternal weight gain: 1 in every 8 low weight births Smoking during pregnancy: 1 in every 14 low weight births Compared to the study, no change in inadequate weight gain contribution, but a large drop in smoking contribution Smoking prevalence declined 25%

Conclusions Inadequate weight gain and smoking during pregnancy still contribute to low birth weight Prevalence of smoking during pregnancy declined which decreased its contribution to low birth weight Public health implication – If programmatic efforts move pregnant women towards adequate weight gain and increase smoking cessation prior to conception, low birth weight births could be reduced. – Hypothetical state low birth weight rate = 7.5% Actual 2009 LWB rate = 8.8%

Strengths & Limitations Strengths – Large birth cohort to study Able to stratify Limitations – Not all LBW risk factors are included on birth certificate Example: maternal stress

Recommendations for Colorado Continue to – Counsel women on smoking cessation before conception and during pregnancy – Encourage women to gain an adequate amount of weight during pregnancy

Recommendations for All Future Tasks Focus public health efforts to improve preconception and interconception health Opportunities for program collaboration

Acknowledgments Colorado Department of Public Health and Environment – Barbara Gabella. MSPH – Indira Gujral, MS, PhD – Sue Ricketts, MA, PhD – Linda Archer, MSN, RN, CNS – Mandy Bakulski, RD – Kirk Bol, MSPH – Epidemiology, Planning and Evaluation Branch The Prenatal Program of the Women's Health Section and Grant Number B04MC17035 from the Maternal and Child Health Bureau (Title V, Social Security Act), Health Resources and Services Administration, Department of Health and Human Services supports this project. The findings and conclusions in this presentation are those of the author(s) and do not necessarily represent the views of the Colorado Department of Public Health and Environment.

Questions & Comments Thank You

References Births: Preliminary data for National Center for Health Statistics. Ricketts S, Trierweiler K, Colorado. Dept. of Public Health and Environment. Tipping the scales : weighing in on solutions to the low birth weight problem in Colorado. Denver, Colo. (4300 Cherry Creek Drive South, Denver 80246): Colorado Dept. of Public Health & Environment; Colorado Birth Certificates, Vital Statistics Section, Colorado Department of Public Health and Environment. Centers for Disease Control. National Environmental Public Health Tracking Network.