Fetal MAP (Novatrans II, MX860, Medex Inc., Hilliard, OH, USA), corrected for maternal movement by subtraction of amniotic pressure, CaBF, and ECG, were recorded continuously throughout the experiment.
5 min (baseline period), 5 sec, and 1 min averages of T/QRS ratio, FHR, MAP, and CaBF were calculated for each fetus, respectively.
The within-subjects relationship between MAP, CaBF, and T/QRS ratio for selected occlusion periods (1 min data) was determined by regression analysis using the methodology of Bland and Altman .
Baseline T/QRS ratio, FHR, MAP, and CaBF are shown in Table 1.
Fetal Heart Rate, Mean Arterial Pressure, and CaBF. Umbilical cord occlusion was associated with a rapid initial fall in FHR from baseline in all gestational groups by 61.2 [+ or -] 1.5% within the first minute; the relative magnitude of this fall was not different between groups (N.S.).
Occlusion was associated with a rapid but brief rise in CaBF followed by a temporary fall before recovering back to baseline values at all gestational ages.
The initial hypertension at the beginning of occlusion was associated with a brief increase in CaBF followed by maintenance around baseline values until approximately 6 minutes at all gestations.
From 8 minutes of occlusion onwards, the fall in MAP below baseline was strongly correlated with a concordant fall in CaBF at all gestational ages.
Perhaps more surprising was that CaBF fell below its relative baseline two minutes before MAP reached baseline.