Fetal-maternal gas transport and acid – base balance in preterm labors

Abstract

The use of cord blood gases to predict hypoxic stress during high-risk labor has been known since 1958. This diagnostic test is widely used, especially in specialized clinics, and blood indicators in the umbilical artery accurately reflect the condition of the newborn. However, there is a lack of specific diagnostic criteria for premature births.The objective: to study the ratio of indicators of gas exchange and acid-base status between the newborn and the mother depending on the gestational age at the time of delivery.Materials and methods. The levels of pH, pO2, pCO2, bicarbonate ion concentration (HCO3-) and base excess (BE) were analyzed both in mothers (maternal venous blood, v. cubitalis) and in their newborns (venous blood obtained from the umbilical artery).Study groups: I group – 16 postpartum women with newborns at 24–27 weeks of gestation, II group – 36 postpartum women with newborns at 28–34 weeks, III group (control group) – 24 postpartum women with newborns at term physiological delivery (37–41 weeks).Results. The study found no statistically significant differences in maternal venous and umbilical artery of pH, pO2, pCO2, HCO3- and BE levels between the term pregnancy group and the groups of preterm labor. However, extremely preterm neonates were found to have a marked increase in pH and BE in response to hyperventilation during labor.Conclusions. 1. Preterm infants had higher venous blood pH levels obtained from the umbilical artery, which were more pronounced in those who were born at earlier gestational ages (7.36±0.011 at 24–27 weeks gestation and 7.33±0.022 at a gestation period of 28–34 weeks), compared to full-term children (7.29±0.045; p<0.05).2. The difference in the pH levels of the venous blood of the newborn, obtained from the umbilical artery, and the mother’s blood, obtained from the v. cubitalis, is smaller in premature births (for a gestation period of 24–27 weeks – 7.39±0.018 in maternal blood and 7.36± 0.011 – in newborns; for the period of 28–34 weeks – 7.40±0.021 and 7.33±0.022, respectively) compared to the levels in full-term babies (7.43±0.015 – in maternal blood and 7.29±0.045 – in a newborn); p<0.05. This is primarily due to a decrease in the mother’s venous blood pH.