End-tidal breath carbon monoxide measurements are lower in pregnant women with uterine contractions

Objective: To compare the levels of end-tidal carbon monoxide (ETCOc) among women with and without uterine contractions in term and preterm pregnancies. Study Design: In all, 55 nonsmoking healthy pregnant women were enrolled. ETCOc levels were compared among women with contraction (10 preterm and 13 term) and 32 women without contraction (34-41 weeks gestation). Results: Maternal age, gravidity and parity were similar amon study and control groups. ETCOc levels were significantly lower among women that had uterine contraction (0.99±0.38 part per million (ppm) and 1.15±0.34p.p.m. respectively), compared to women with no contractions (1.70 ± 0.52 p.p.m, P<0.002). However,there was no significant difference in the ETCOc levels between women with preterm or term contractions (P=0.48). Conclusions: Low levels of ETCOc are associated with preterm and term uterine contractions.