Association between maternal pre-pregnancy BMI and breastfeeding initiation rates among WIC program participants

WIC program prenatal breastfeeding education and support (BFES) is targeted specifically toward women who are least likely to adopt breastfeeding. Modifiable risk factors for these women are identified at enrollment and customized BFES is provided accordingly, to achieve breastfeeding goals. However, pre-pregnancy BMI is not frequently considered a risk factor for breastfeeding initiation.

This study explores the relationship between pre-pregnancy BMI and breastfeeding initiation. We analyzed 25,333 WIC program participating pregnant women who also participated during post-partum period as mother-infant dyads in 2008. We measured breastfeeding initiation rates at enrollment and computed pre-pregnancy BMI for weight status classification per CDC guidelines.

On average, mothers were 26 years old, had an annual household income of $16,308 and 65.5% were at or below poverty threshold. Almost half (49.1%) were African Americans, a quarter were Hispanic and 22.1% were non-Hispanic Whites. More than a fifth (21.1%) were enrolled in WIC during 3rd trimester. LBW and preterm birth rates were 8.3% and 14.4%, respectively.

Exclusive breastfeeding was 7.5% while “any” breastfeeding (includes partial and exclusive) to measure breastfeeding initiation rate (BFIR), was 59.2%.

Average pre-pregnancy BMI was 27.2 (s.d=7). Based on BMI, weight status classification included: 5.8% underweight, 39.6% normal, 27% overweight, 21.9% class I obese and 5.7% class II obese.

We observed an inverse “U” shape of the relationship between pre-pregnancy BMI and BFIR. Women classified as underweight had the lowest BFIR (50.3%), which increased with increased weight category (56.5% for normal, 63.5% for overweight), but showed lower BFIR for obese class I (56.3%) and class II (49.8%) obese participants (p<0.001), respectively. This inverse “U” shape relationship remained when we conducted multiple regressions using normal weight participants as reference. Underweight participants had 22% lower risk of breastfeeding initiation than normal weight participants (O.R.=0.78;95%CI=0.70-0.88;p<0.001). Compared to normal weight participants, the odds of breastfeeding initiation was 1.02 (95%CI=0.95-1.08;p=NS) for overweight participants, 0.83 (95%CI=0.77-0.89;p<0.001) for class I obese participants, and 0.74 (95%CI=0.66-0.83,p<0.001) for class II obese participants, after maternal and infant socio-demographic and health factors were controlled. Annual analysis for four previous years (2004-2007) yielded similar results.

Our results suggests implications for targeting both underweight and obese WIC program participants for education, promotion and support to improve breastfeeding initiation rates.