Assessment of the risk of fetal loss after the coelocentesis procedure using a baboon model

The aims of this study were to gain some insight with regard to the safety of the coelocentesis procedure and, to determine pH, pCO2, and base excess status of the extracoelomic fluid 40 days after fertilization.

Twenty-eight timed-mated baboons from the breeding colony of the Biological Resource Laboratory at the University of Illinois at Chicago were studied. The initial 19 animals were used to determine the ultrasonographic relations between the different compartments of the gestational sac from 38 to 62 days of pregnancy. Under aseptic conditions, in 9 animals coelocenteses were then performed, under continuous transvaginal ultrasound guidance to avoid the amniotic or yolk sacs. Extracoelomic fluid (1-5 ml) was aspirated using 10-ml syringes. Only one attempt of sampling was performed in each of the 9 animals. Extracoelomic fluid pH, pCO2, and base excess were compared with maternal femoral venous blood. Pregnancies were followed by transabdominal ultrasound evaluations on day 3 after the procedure and weekly until day 140 after fertilization.

Extracoelomic fluid could be aspirated easily using a 20-gauge needle. Only one pregnancy loss was detected within 3 days after the procedure. No complications occurred in the remaining 8 pregnancies. Extracoelomic fluid pH (7.45 +/- 0.01) and pCO2 (39.9 +/- 2.4 mm Hg) were significantly different from maternal femoral venous blood pH (7.41 +/- 0.01) and pCO2 (47.1 +/- 1.4 mm Hg; p < 0.02), while base excess values were similar.

This preliminary study performed at 40 days after fertilization in the baboon model suggests that the coelocentesis procedure is technically simple and presents a relatively low risk to mother and fetus if a 20-gauge needle is used and the amount of aspirated extracoelomic fluid is <3 cm3. At this gestational age, the extracoelomic fluid is more alkalotic than maternal femoral venous blood.