Uterine artery Doppler evaluation in twin pregnancies at 11+0 TO 13+6 weeks of gestation

Objective To compare uterine artery pulsatility index(PI) obtained at 11 + 0-13 + 6 weeks in singleton and twin pregnancies and to evaluate changes in PI values of twin pregnancies developing pre-eclampsia (PE) or small for gestational age (SGA) of either one or both fetuses. Methods Uterine artery PI was measured in 421 twin pregnancies (384 dichorionic, 37 monochorionic) and in 500 singleton pregnancies. The measured mean and lowest uterine artery PI values was converted to multiples of the expected normal median (MoM) after correction for maternal body mass index, ethnicity and gestational age. The median PI MoM values of twins were compared with singleton pregnancies. In twin pregnancies PI MoM values were analyzed according to chorionicity, development of early onset (<34 weeks), late onset PE (≥34 weeks) and SGA of one or both twins Results Uterine artery PI MoM was significantly lower in twin pregnancies vs. singleton pregnancies (mean value K =174.31, p≤0.0001, lowest value K =139.27, p≤0.0001). However, there were no significant differences in the uterine artery PI MoM values between monochorionic and dichorionic twins. The uterine artery PI in twin pregnancies who developed early onset PE (p ≤ 0.001) and SGA of both twin (p ≤ 0.05) was higher than in uncomplicated twin pregnancies, while no differences were found for late PE or SGA of one twin. Conclusions First-trimester placental impedance to flow, as assessed by uterine artery Doppler examination, is reduced in twin pregnancies with no differences related to chorionicity. The relative increase of uterine artery PI found in twin pregnancies that developed early PE and SGA of both twins suggests that first trimester uterine artery assessment may be useful in identifying such complications