Placental mesenchymal dysplasia: a rare case associated with second trimester fetal growth restriction

Placental mesenchymal dysplasia (PMD) is a rare, benign, placental disorder characterised macroscopically by an enlarged multi-cystic placenta. It is a condition associated with a range of reported clinical outcomes and can be misdiagnosed as a molar or partial molar pregnancy given the similarities in clinical presentation. We present an unusual case of PMD complicated by fetal growth restriction and oligohydramnios in the second trimester.

A 33 year old female was referred to our fetal medicine unit with a multi-cystic placenta at dating scan suspected initially to be a partial molar pregnancy. She opted for conservative management and declined invasive testing. At 16 weeks severe fetal growth restriction was present with an estimated fetal weight < 3rd centile and associated with oligohydramnios. Whilst live births in cases of PMD have been reported in the literature, to our knowledge there are no reported successful outcomes in cases of early onset growth restriction at this gestation. The patient opted to proceed with termination of pregnancy given the suspected poor prognosis. Post mortem results confirmed a diagnosis of PMD and fetal growth restriction with normal genetic testing.

Placental mesenchymal dysplasia can be a difficult condition to manage, particularly when counselling about prognosis and deciding whether to continue the pregnancy. More evidence is needed about prognostic factors in PMD associated with a successful outcome. Early onset fetal growth restriction and/or oligohydramnios prior to 20 weeks are likely poor prognostic factors which should be considered in the antenatal counselling.