Dietary protein: Protection against preterm birth in stressful environments
Louise H. Flick
L.H. Flick, DrPH1, C.L. Cook, PhD2, S.M. Homan, PhD3, M. Mattfield-Beman, PhD4, K.
Pierce, BA4, C. Campbell, PhD5, M. McSweeney, PhD6, L. Parnell, MSW7, M.E.
Gallagher, PhD8.
1
Southern Illinois University Edwardsville, School of Nursing, Edwardsville, Illinois; St.
Louis University: Schools of 2Social Service, 3Public Health, and 6Nursing (emerita),
4
College of Health Sciences and 8Voices Program, St. Louis, Missouri; 5Tulane
University School of Public Health, New Orleans, Louisiana, 7St. Luke's Hospital,
Chesterfield, Missouri; USA.
BACKGROUND: Maternal stress in pregnancy inhibits fetal growth and increases risk
of preterm birth yet only about 10% of the stress hormone cortisol crosses the placenta.
Animal studies indicate that the placenta produces an enzyme that blocks placental
transfer of cortisol. When protein consumption in mother rats is below recommended
pregnancy levels, enzyme production ceases and cortisol transfer increases 10-fold.
OBJECTIVE: To test the hypothesis that environmental stress interacts with prenatal
protein consumption in human mothers in the prediction of gestational age and preterm
birth.
MATERIALS & METHODS: In a representative, prospective cohort study of lowincome pregnant women, we analyzed data from pregnancy assessments of 500 women
enrolled in a prenatal poverty nutrition program. Women were 60% African American
and 40% Caucasian with 72% residing in rural area in the Midwest, with the remainder
being urban; 25.8% reported protein intake below 85% of the US National Academy of
Sciences' recommended daily allowance (RDA) for pregnancy, 16% of births were
preterm (<37 weeks) and 2.6% very preterm (<32 weeks). Gestational age was
determined by last menstrual period, obtained via interview, with birth date from birth
certificates. A self-report measure, modified from the CDC's PRAMS study, summarized
stressful events, stressful relationships and financial stressors in the past year. Protein
intake was measured as percent of RDA using the Harvard Food Frequency Index which
summarizes the past month's food intake. Analyses consisted of multiple linear and
binary logistic regressions adjusting for race, mother's age, parity, and pre-pregnancy
body mass index. RESULTS: Results show a significant interaction between stress
scores and protein consumption in the prediction of gestational age and preterm birth but
not for very preterm birth.
CONCLUSION: In this low income sample, prenatal protein consumption below 85% of
the pregnancy RDA amplifies the effect of a given level of stress on the fetus in
decreasing gestational age at birth and increasing risk of preterm birth. Implications for
public health include reinforcement of the importance of consuming recommended levels
of protein in pregnancy especially for women in stressful social environments.