From biochemical to biophysical placental function tests in fetal surveillance

Radioimmunoassays of human placental lactogen and estriol levels in the maternal plasma, ultrasound biometry of the abdominal diameter (AD), pulsed Doppler measurements of uteroplacental arteries, the common carotid artery (CCA), and the umbilical artery (UA) and fetal heart rate monitoring were simultaneously performed in 219 risk pregnancies from 26 weeks' onward at regular intervals. The prognostic value of all tests to predict small for gestational age infants (SGA) and fetal distress was evaluated simultaneously. Receiver operator characteristic allowed the simultaneous comparison of all methods: The AD was most predictive for early detection of SGA, even more than uteroplacental blood flow. Fetal blood flow redistribution expressed as a ratio of the resistance index of CCA/UA was the most significant test for detection of fetal distress later in pregnancy, even more than antenatal cardiotocography. Considering cutoff levels used in clinical routine, the sensitivity and specificity of the fetal AD in detecting intrauterine growth retardation more than 28 days before birth, were 71 and 81%, respectively. Pulsed Doppler measurements of CCA/UA less than 7 days before the delivery had a sensitivity and specificity of 83 and 90%, respectively. Our results demonstrate the historical change in fetal surveillance within one study group: If accurate routine ultrasound is available, the use of biochemical placental function tests is not justified, a procedure that is already accepted in nearly all perinatal centers. Fetal cerebral versus umbilical blood flow measurements should be applied as a tool to measure fetal blood flow redistribution in small fetuses to predict most precisely the risk for poor outcome and perinatal hypoxia.