Alterations of occlusive cuff impedance plethysmography results in the obstetric patient.

Impedance plethysmography (IPG) is an attractive diagnostic method for evaluating deep vein thrombosis in the pregnant patient because it is noninvasive and it avoids x-ray or radionuclide exposure. However, the accurate diagnosis of deep venous thrombosis by IPG in pregnant patients might be altered by the normal physiologic and anatomic changes that occur during pregnancy. We evaluated 50 healthy women by IPG throughout their pregnancies and during their nonpregnant state. We found that venous capacitance during pregnancy increases 50% over venous capacitance during the non pregnant state. Most of this change occurs during early pregnancy because of a decrease in venous tone caused by rising levels of progesterone and estradiol. During the third trimester of pregnancy venous outflow is diminished compared to outflow during early pregnancy. Venous obstruction by the gravid uterus and fetal head engaging in the pelvis are factors that contribute to this finding. The IPG results in four patients with ileofemoral thrombosis and in three with postpartum pulmonary emboli are also reported. IPG may be utilized as an accurate diagnostic technique in the pregnant woman if the physiologic and anatomic alterations of pregnancy, which are reflected as significant changes in venous capacitance and outflow on IPG testing, are considered.