What is placental mesenchymal dysplasia?

Placental Mesenchymal Dysplasia (PMD)

Placental mesenchymal dysplasia (PMD) is a rare vascular and connective placental anomaly characterized by placentomegaly and grape-like vesicles that can be confused with molar pregnancy, but unlike molar pregnancy, PMD can coexist with a viable fetus with normal karyotype. 1

Definition and Pathophysiology

• PMD is a rare placental abnormality with an enlarged placenta and multiple vesicular lesions that resemble molar pregnancy on ultrasound examination 2
• Unlike placenta accreta spectrum disorders (which involve abnormal trophoblast invasion into the myometrium), PMD is a morphological abnormality of the placental vasculature and connective tissue 3, 1
• PMD is characterized by hydropic degeneration of stem villi, placentomegaly, and often increased maternal serum alpha-fetoprotein (AFP) 4

Epidemiology and Risk Factors

• The true incidence of PMD remains unknown due to its rarity and potential underdiagnosis 5
• Mean gestational age at diagnosis is approximately 23 weeks (range 16-39 weeks) 1
• No consistent clinical risk factors have been established for PMD development 1

Clinical Presentation and Diagnosis

Prenatal Features

• Ultrasound findings typically show an enlarged placenta with multiple vesicular lesions resembling molar pregnancy 2
• Prenatal biochemical screening may be abnormal in approximately 36% of cases 1
• Normal maternal human chorionic gonadotropin (hCG) levels help differentiate PMD from molar pregnancy 2

Diagnostic Challenges

• PMD is frequently misdiagnosed as partial molar pregnancy due to similar ultrasound appearance 6
• Accurate diagnosis is essential as management differs significantly between these conditions 6
• Definitive diagnosis is usually achieved through postpartum histological examination of the placenta 6

Diagnostic Tools

• Chorionic villus sampling or amniocentesis showing normal fetal karyotype in the presence of molar-like placental changes supports PMD diagnosis 2
• Cytogenetic ploidy analysis and p57KIP2 protein staining are useful in differentiating PMD from partial molar pregnancy 6

Maternal and Fetal Complications

Maternal Complications

• Approximately 27% of mothers with PMD develop complications such as preeclampsia or gestational hypertension 1
• Despite the abnormal placental appearance, many pregnancies with PMD can progress without maternal complications 4

Fetal Complications

• Fetal growth restriction occurs in approximately 50% of PMD cases 1
• Intrauterine fetal death is reported in about 18% of cases 1
• Only about 14% of pregnancies with PMD progress normally to term 1
• Among live births, approximately 35% may experience neonatal death within the first two months 1
• Transient thrombocytopenia is observed in about 35% of live-born infants 1
• PMD has been associated with Beckwith-Wiedemann syndrome and other genetic abnormalities 6
• Cases of sudden intrauterine death have been reported even in normal-sized fetuses with no prior signs of distress 2

Associated Conditions

• PMD has been associated with various conditions including:
  • Beckwith-Wiedemann syndrome 6
  • Placental triploidy mosaicism 1
  • CHARGE syndrome 1
  • Fetal pleuropulmonary blastoma 1
  • Fetal skeletal dysplasia 1

Management Considerations

• Due to the high risk of adverse fetal and maternal outcomes, close pregnancy monitoring is essential 1
• Careful ultrasound evaluation is crucial to distinguish PMD from partial molar pregnancy 5
• In cases with placental ultrasound anomalies but no signs of fetal distress, the pregnancy should still be considered high-risk 2
• Hospitalization may be considered as part of management in some cases 2
• Genetic testing should be discussed to exclude partial molar pregnancy 1

Key Pitfalls in Diagnosis and Management

• PMD is substantially underdiagnosed before delivery 1
• Misdiagnosis as molar pregnancy may lead to unnecessary pregnancy termination 6
• Normal fetal growth and absence of distress signs do not exclude the possibility of sudden intrauterine death 2
• Sonographers, fetal medicine specialists, obstetricians, and pathologists should suspect PMD in cases of enlarged placenta with vesicular changes 1