Is fetal blood sampling associated with increased beta-endorphin release into the fetal circulation?

This study was conducted to determine whether fetal blood sampling during the second trimester is associated with changes in circulating fetal beta-endorphin (BE) concentrations. We measured BE concentrations in 68 paired fetal and maternal blood samples obtained between 18 and 28 weeks' gestation. Patients were divided into a control group (n = 50), if the fetal blood samples were obtained by a single umbilical cord puncture, or multiple insertion group (n = 18), if multiple cord punctures were required to obtain a sample. The mean (+/- SE) fetal BE value for the multiple insertion group was significantly higher than BE levels from the control group (771.2 +/- 79.2 pg/ml versus 107.1 +/- 11.7 pg/ml; p < 0.001]. This elevation did not appear to be related to acidosis, since no differences in fetal umbilical pH were observed between the two groups. Fetal BE levels from the control but not from the multiple insertion group significantly correlated with maternal values (Spearman rank r = 0.59; p < 0.001 vs r = -0.08; p > 0.5). In neither group did fetal BE levels correlate with gestational age. These findings indicate that multiple cord punctures at the time of fetal blood sampling are associated with significant increases in BE release. Furthermore, although a maternal or placental contribution to steady state circulating fetal BE cannot be excluded, it would seem that the fetus itself is the primary source of elevated circulating BE levels following multiple cord punctures.