**2.2 Sampling procedures**

Fetal blood was obtained by cordocentesis from the umbilical vein, a technique carried out without maternal premedication, and only under local anesthesia at the puncture site (Daffos, 1983).

Five hundred microlitres of umbilical venous blood were collected in a heparinised syringe for gasometric and acid-base analyses, pH, partial CO2 pressure (pCO2), bicarbonate concentration, partial oxygen pressure (pO2) and oxygen saturation (SaO2).

The concentrations of ketone bodies (aceto-acetate and beta-hydroxybutyrate), free fatty acids (FFA) and cholesterol were evaluated on the same sample.

Two hundred microlitres of umbilical venous blood were collected on sodium fluoride to measure glucose and lactate, and 200 µl were collected without anticoagulant to measure hCG.

The good quality of the sample was verified, in particular the absence of contamination by maternal blood or amniotic fluid (Forestier, 1988). An immediate check was made by determining the erythrocyte group iI, and then a Kleihauer test, red and white cell count and a leukocyte differential count were carried out.

The serum hCG concentration of fetal blood was also measured, this test being proposed as a sensitive contamination marker due to the low hCG content of fetal serum, compared with that of the maternal blood and / or amniotic fluid (Dommergues et al., 1993).

Fetal blood samples were stored in ice at +4°C and transported to the laboratory immediately. The blood pH and gas measurement and the deproteinisation of the whole blood with perchloric acid for the ketone bodies determination were carried out upon receipt of the samples; the deproteinisation supernatants were decanted and kept at -20°C.

The blood was centrifuged at +4°C for the other analyses. The plasma glucose, lactate, cholesterol and hCG concentrations were determined immediately; the free fatty acid contents were determined subsequently on the plasma kept at -20°C.

The sample storage conditions were verified for the quantitative analysis carried out after freezing.
