#Grand Rounds

Does Low-Level Prenatal Passive Tobacco Exposure Decrease Breastfeeding Duration?

BACKGROUND AND PURPOSE:

Environmental contaminants, including tobacco smoke, lead and phthalates, are transferred from mothers to infants transplacentally and via breast milk
Most studies have evaluated impact of toxins on breast feeding by focusing on exposure via breast milk
Few studies have focused on low-level exposures to toxins in the prenatal period
Rosen–Carole et al. (Maternal and Child Health Journal, 2017) assessed the impact of low prenatal exposure to common toxins (tobacco smoke, lead, and phthalates) on breastfeeding exclusivity and duration

Prospective cohort study
Health Outcomes and Measures of the Environment (HOME) Study (2003-2006)
Serum and urine samples were collected at approximately 16 (range 10-23) and 26 (range 19-35) weeks gestation and at delivery
Women were included who lived in a home built in 1978 or before, when lead-based paints were frequently used
Maternal infant feeding interviews were conducted eight times through 30 months postpartum, beginning 4 weeks post partum
Tobacco smoke
- Passive smoke exposure defined as serum cotinine levels of 0.015-3.0 μg/mL)
- Active smokers defined as serum cotinine concentrations >3.0 μg/mL
Cotinine, lead, and phthalates measured at the CDC Division of Laboratory Sciences
Primary outcomes were duration of any and exclusive breastfeeding

Samples were collected from 373 women; 302 breastfed their infants
As serum cotinine concentrations increased, duration of any breastfeeding decreased
- 29.9 weeks unexposed vs. 24.9 weeks with passive exposure (p = 0.04)
Duration of any breastfeeding was not significantly different between active smokers and the unexposed group but there was a linear trend for increasing cotinine levels (p = 0.03 for linear trend)
- Only 12% of women were active smokers and ‘n’ may be too small to detect difference
There was no difference in duration for exclusive breastfeeding
Prenatal levels of blood lead and urinary phthalate metabolites were not significantly associated with duration of any or exclusive breastfeeding
More women in passively and actively exposed groups did not feel they had breastfed for as long as intended compared with unexposed women
- 21% felt they did not meet their goals because of return to work while 49% felt their breast milk was insufficient or reported growth failure for their infants

Researchers acknowledge study limitations, including potential lack of generalizability as the HOME cohort generally had lower rates of exclusive breastfeeding and briefer breastfeeding compared to national cohorts
This study does not address biologic explanation but other researchers have suggested toxic impact on development of mammary glands during pregnancy or disruption of hormonal signaling
Hypothesis supported by at least one animal study
Passive exposure to tobacco smoke during pregnancy was associated with shortened duration of any breastfeeding even after adjusting for confounders

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