Investigation of the acid-base balance of coelomic and amniotic fluids in early human pregnancy.

OBJECTIVE

The aim of our study was to analyze and compare the acid-base status of coelomic and amniotic fluids in early human pregnancy.

STUDY DESIGN

Coelomic fluid, amniotic fluid, and maternal serum were obtained from 55 normal pregnancies between 7 and 14 weeks of gestation and assayed for pH, PCO2, bicarbonate, chloride, phosphate, total protein, glucose, and lactate concentrations.

RESULTS

The coelomic fluid had a significantly lower pH and base excess and contained significantly lower glucose, total protein, and bicarbonate concentrations and higher PCO2, lactate, and phosphate levels than did maternal serum. In the amniotic fluid significantly higher pH, base excess, and lactate and bicarbonate levels and lower concentrations of chloride and phosphate were found compared with the coelomic fluid. Little variation was observed in the coelomic and amniotic fluid composition before 11 weeks of gestation. A significant increase in PCO2, total protein, and chloride levels and a decrease in pH, base excess, and bicarbonate concentrations were observed in the amniotic fluid between 11 and 14 weeks compared with 7 to 10 weeks.

CONCLUSIONS

The coelomic fluid composition was indicative of an anaerobic metabolic acidosis probably related to the accumulation of acid compounds from placental metabolism. During the same period of gestation the composition of the amniotic fluid demonstrated a metabolic alkalosis that probably arises from the accumulation of basic substances through the unkeratinized embryonic skin and from the metabolism of organic anions in the embryonic tissues. The changes in the amniotic composition and acid-base balance at the end of the first trimester may correspond to the switch from the mesonephros to the metanephros and result from the excretion in the amniotic fluid of acid metabolic fetal bioproducts through the maturing kidneys.