Extravillus endovascular implantation site trophoblast invasion is abnormal in complete versus partial molar pregnancies.

This study examines endovascular trophoblast invasion in pregnancies complicated by complete hydatidiform mole (CM), partial hydatidiform mole (PM) and non-molar abortions (HA). Two hundred consecutive cases from a supra-regional referral centre for suspected trophoblastic disease were examined histologically with particular regard to the presence or absence of endovascular trophoblast invasion of decidual vessels. There were 57 CM, 75 PM and 68 HA. The prevalence of normal endovascular invasion of decidual vessels was significantly lower in CM compared to all other clinical groups, amongst which there were no significant differences. Endovascular trophoblast was identified in about 80 per cent of HA and PM moles, compared to only around 25 per cent of CM (Z = -4.0, P< 0.0001). The majority of cases of complete mole demonstrated a similar appearance, of implantation site showing florid interstitial extravascular trophoblast invasion with surrounding of decidual vessels but without normal endovascular trophoblast invasion or 'plugging' seen. In many cases, there also appeared to be destruction of decidual vessels with interstitial haemorrhage and extensive fresh blood clot present in the histological sections. These findings may provide some explanation regarding the mechanism of clinical findings in molar pregnancy. Copyright 2001 Harcourt Publishers Ltd.