Objectives: We sought to investigate the fetal hemodynamic response to the acute stress of invasive procedures.
Study design: The middle cerebral artery pulsatility index was measured by Doppler ultrasonography before and after 136 invasive procedures (fetal blood sampling, transfusion, shunt insertion, tissue biopsy, and ovarian cyst aspiration). The response of fetuses submitted to invasive procedures involving transgression of the fetal body, such as intrahepatic vein blood sampling, was compared with that of control procedures at the placental cord insertion.
Results: The middle cerebral artery pulsatility index value fell with fetal blood sampling performed at the intrahepatic vein (median, -0.26; 95% confidence interval, -0.35 to -0.15) but not at the placental cord insertion (median, 0.05; 95% confidence interval, -0.04 to 0.19). With transfusions, the middle cerebral artery pulsatility index also fell with procedures at the intrahepatic vein (mean, -0.51; 95% confidence interval, -0.66 to -0.35) but not at the placental cord insertion (mean, -0.04; 95% confidence interval, -0.23 to 0.14). The magnitude of the response was greater with transfusions than with blood sampling alone. The middle cerebral artery pulsatility index value also fell with non-fetal blood sampling procedures involving transgression of the fetal body (mean, -0.32; 95% confidence interval, -0.56 to -0.09) but not with control non-fetal blood sampling procedures. The change in the middle cerebral artery pulsatility index was not related to gestational age, with the youngest fetus showing a fall in the middle cerebral artery pulsatility index value being at 16 weeks' gestation. Although the degree of response was weakly correlated with the duration of needling (y = -0.21 - 0.00014x; R (2) = 0.08; P =.02), multiple logistic regression demonstrated that this was instead a function of the type of the procedure. A response was seen within 70 seconds of fetal puncture. The fetal heart rate did not change significantly with procedures in any of the above-mentioned groups.
Conclusions: The human fetus mounts a cerebral hemodynamic response to invasive procedures involving transgression of the fetal body, which is consistent with the brain-sparing effect.