Activated protein C sensitivity ratio in pregnant women at delivery.

We studied activated protein C sensitivity ratio (APC-SR), factors V and VIII activity and von Willebrand antigen in control women, women using oral contraceptives, and pregnant women at delivery. The mean APC-SR of 2.4 in pregnant women was significantly lower than the mean APC-SR value of 3.5 for both the other groups and 45% of pregnant women had a ratio below the 5th percentile of the control group. None of them carried the R506-->Q mutation. This decreased ratio at delivery appeared to be connected, at least in part, with increased VIII activity. Thus, APC-SR at delivery should not be used to detect APC resistance.