Association of fetal and maternal carboxyhemoglobin levels in normal and Rh-alloimmune pregnancies

Objective: To compare paired antepartum fetal/maternal COHb ratios in whole blood from control and alloimmunized pregnancies and to examine the relati onships between fetal and maternal COHb. Methods: COHb levels were measured in paired fetal and maternal blood samples obtained at cordocentesis in 47 control and 16 Rh-alloimmunized pregnancies. COHb was determined by gas ch romatography. Results were analyzed by t-test, regression and analysis of c ovariance. Results: Although fetal/maternal COHb ratios for control and all oimmunized pregnancies were not statistically significantly different, i.e. 1.11+/-0.04 and 1.26+/-0.09, respectively (P = 0.09), fetal COHb levels we re higher in Rh-alloimmunized fetuses (P = 0.0002). Fetal COHb levels were also higher than paired maternal levels among the alloimmunized group (P = 0.011), but not among the control group (1.04+/-0.04, P = ns). In univariat e regression analysis, fetal and maternal COHb levels were significantly co rrelated with one another in both control (r = 0.52, P = 0.0002) and alloim munized pregnancy groups (r = 0.52, P = 0.05). Comparison of the slopes of the fetal versus maternal COHb plots for the two groups showed a significan t difference (P = 0.02), with the alloimmunized group having the steeper sl ope. Conclusion: Differences in the antepartum fetal-maternal COHb relation ships in control and alloimmunized groups likely reflect increased endogeno us CO production among alloimmunized fetuses as a result of pathologic hemo lysis. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.