Placental Mesenchymal Dysplasia

Placental mesenchymal dysplasia is a rare condition of the placenta with enlargement and grape like cystic vesicles from dilated stem villi, which looks like a partial mole but has a normal diploid karyotype and a fetus that is usually normal. It is more common in female fetuses. It matters because it is linked with fetal growth restriction, stillbirth, preterm birth and Beckwith-Wiedemann syndrome, and must be told apart from a molar pregnancy.

• Risk factors: Beckwith-Wiedemann syndrome in the fetus, assisted conception, female fetus.
• Maternal human chorionic gonadotrophin is normal or mildly raised.
• Placental histology and p57 staining confirm the diagnosis.

Women are usually well, with a uterus that may be large for dates and a normally formed fetus on scan. Some have bleeding, preeclampsia features or reduced movements.

• Fundal height above or below dates.
• Hypertension in some.
• Differential diagnosis: partial hydatidiform mole, complete mole with a coexisting twin, chorioangioma, placental haematoma, triploidy, normal placental cysts.
• Complications: fetal growth restriction, stillbirth, preterm birth, preeclampsia, fetal macrosomia and organomegaly in Beckwith-Wiedemann syndrome, hepatic mesenchymal hamartoma, neonatal hypoglycaemia.

The approach is ultrasound, hormonal and genetic tests to distinguish it from a partial mole.

• Ultrasound: enlarged thickened placenta with multiple cystic spaces and a normal fetus with normal growth or growth restriction; umbilical vein and stem vessel dilatation; liver and kidney assessment.
• Serum human chorionic gonadotrophin (normal or mildly raised), maternal serum alpha fetoprotein (often raised).
• Amniocentesis for karyotype: diploid 46,XX or 46,XY confirms the condition and excludes triploidy; molecular testing for chromosome 11p15 where available.
• Placental histology with p57 immunostaining after birth; fetal growth and Doppler scans.

The principle is to confirm a diploid fetus, to monitor growth and to plan delivery at 37 to 38 weeks with newborn genetic review.

• Supportive: refer to a fetal medicine unit; counselling on the benign nature of the placenta and the risk of growth restriction; daily fetal movement counts; delivery in a unit with neonatal care.
• Pharmacological: aspirin 150 mg oral at night from diagnosis to 36 weeks if preeclampsia risk is high; labetalol 200 mg oral every 8 to 12 hours (maximum 2.4 g daily) or nifedipine modified release 30 to 60 mg oral once daily (maximum 120 mg) for blood pressure 140/90 mmHg or more; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if delivery is likely; oxytocin 10 IU IM at birth; newborn dextrose 10 percent 2 mL/kg IV over 10 minutes then 80 mL/kg per day for glucose below 2.6 mmol/L.
• Procedures: growth scans every 2 weeks with umbilical artery Doppler; delivery at 37 to 38 weeks, earlier for growth restriction, abnormal Doppler or abnormal cardiotocography; no chemotherapy or uterine evacuation, because it is not a molar pregnancy.
• Special groups: fetuses with features of Beckwith-Wiedemann syndrome (macroglossia, abdominal wall defect, organomegaly) need delivery in a tertiary unit and a newborn genetic review with glucose monitoring.
• Red flags: falling growth centile, reduced fetal movements, hypertension, abnormal Doppler, polyhydramnios.
• Follow-up: antenatal review every 2 weeks; newborn ultrasound of the abdomen and liver; placental histology; genetic counselling for the next pregnancy.