Maternal hyperventilation during labor revisited: its effects on fetal oxygenation.

To investigate the relationship between maternal hyperventilation and fetal blood gas values and to estimate its possible association with fetal oxygenation, maternal transcutaneous partial pressure of carbon dioxide (tcP(CO2)) values were analyzed in association with umbilical venous P(CO2) (UVP(CO2)), umbilical venous partial pressure of oxygen (UVP(O2)), and umbilical venous oxyhemoglobin saturation (UVHbo (2)) values. Pregnant women without labor (30.7 ± 3.7 mm Hg, n = 20) showed significantly lower tcP(CO2) values compared with nonpregnant women (37.4 ± 4.0 mm Hg, n = 10). Pregnant women in the second stage of labor showed even lower tcP(CO2) values compared with pregnant women during the first stage of labor (20.8 ± 5.9 mm Hg vs 28.4 ± 5.0 mm Hg, n = 26). Maternal tcP(CO2) values had significant positive correlations with UVP(CO2) (r = .78, P < .001), UVP(O2) (r = .62, P < .001), and UVHb(O2) values (r = .59, P < .001). Maternal hyperventilation had a close relationship with lower UVP(CO2), UVP(O2), and UVHbo(2) values, which might interfere with optimal fetal cerebral oxygenation.