REFERENCE RANGES FOR FETAL BLOOD-GAS AND ACID-BASE PARAMETERS DURING THE 2ND AND 3RD TRIMESTERS OF PREGNANCY

Objective: The aim of the study was to establish reference ranges for fetal blood gases and acid-base balance for the second half of the ges tation. Methods: 155 appropriate-for-gestational-age fetuses between 1 8 and 39 weeks of gestation underwent a diagnostic cordocentesis. From a specimen obtained from umbilical venous blood the acid-base balance and blood gases were evaluated using an AVL 995 blood gas analyzer. I n detail, pH, oxygen partial pressure, and carbon dioxide partial pres sure were measured and oxygen saturation, bicarbonate concentration an d base excess calculated. Thereafter. a linear regression for gestatio nal age was calculated and the 95% confidence interval established. Re sults: pH, oxygen partial pressure, and oxygen saturation showed a sig nificant decrease with advancing gestational age, whereas the carbon d ioxide partial pressure increased. The ranges of bicarbonate and base excess did not differ significantly. Conclusion: The results give info rmation about blood gases in the fetus under physiological conditions, and the reference ranges can he used for comparison in fetuses at hig h risk of hypoxia or acidemia.