First trimester markers of preeclampsia in twins: Maternal mean arterial pressure and uterine artery Doppler pulsatility index

Objective: This study aims to evaluate the distribution of mean arterial pressure (MAP) and uterine artery Doppler pulsatility index (PI) in first trimester twins with and without preeclampsia. Method: A total of 147 twins were recruited from a specialist clinic and 110 unaffected singleton pregnancies attending the same institution served as controls. MAP and Doppler PI values were expressed in multiples of the gestation-specific median using published equations. Results: Among the twins, 12 had preeclampsia and two had pregnancy-induced hypertension. Among unaffected pregnancies, there was no significant difference in MAP levels between twins and singletons (P=0.17, Wilcoxon rank sum test, two-tail). However, the Doppler PI levels were highly statistically significantly lower than in singletons (P<0.0005). MAP was unrelated to chorionicity (P=0.46), but there was a statistically significant increase in Doppler PI among monochorionic compared with dichorionic twins (P<0.01). In twins with preeclampsia, MAP was significantly higher than in unaffected twins (P<0.02, one-tail), whereas Doppler PI levels were significantly reduced (P<0.01, two-tail). Conclusion: If first trimester screening for preeclampsia is extended to twins, a different normal median Doppler PI equation will be needed. Contrary to expectations, Doppler PI levels may not be raised in affected twins, although this needs confirmation in a larger study.