[Normal value curves for intrauterine fetal blood gas and acid-base parameters in the 2nd and 3rd trimester].

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 gestation.

METHODS

155 appropriate-for-gestational-age fetuses between 18 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. In detail, pH, oxygen partial pressure, and carbon dioxide partial pressure were measured and oxygen saturation, bicarbonate concentration and base excess calculated. Thereafter, a linear regression for gestational age was calculated and the 95% confidence interval established.

RESULTS

pH, oxygen partial pressure, and oxygen saturation showed a significant decrease with advancing gestational age, whereas the carbon dioxide partial pressure increased. The ranges of bicarbonate and base excess did not differ significantly.

CONCLUSION

The results give information about blood gases in the fetus under physiological conditions, and the reference ranges can be used for comparison in fetuses at high risk of hypoxia or acidemia.