Author’s reply re: Vesicular mole in a twin pregnancy
Sir,
We thank Tsz-Kin Lo for the interest in the mini-commentary1,2. The issues raised by the author are valid. Indeed, the purpose of the mini-commentary was to elaborate on the similarities and differences between vesicular mole in a twin pregnancy, placental mesenchymal dysplasia (PMD) and a partial vesicular mole. The mini-commentary states that trophoblastic proliferation and stromal inclusions are not seen in PMD, implying that the distinction is possible only on pathology. I thank the author for making this explicit. Histopathological diagnosis is unfortunately available only in retrospect. The suggestion to consider amniocentesis for molecular diagnosis of Beckwith-Wiedemann syndrome in a case of suspected complete vesicular mole and an apparently normal fetus in a twin pregnancy signals the challenges of antenatal diagnosis. Such a consideration would be unnecessary if one were to be sure of the diagnosis without the availability of placental histopathology.
Ultrasound is the most common modality for prenatal diagnosis of vesicular mole in a twin pregnancy2. MRI has been described for the detection of molar placenta and a sac separating from fetus and normal placenta in a case of vesicular mole in a twin pregnancy. This would be helpful to differentiate it from PMD or a partial mole with a co-existing fetus. Another possibility is a sub-chorionic haematoma, with which it is confused not infrequently3. However, there are no studies that have investigated the diagnostic accuracy of MR imaging compared to ultrasound in complete vesicular mole with a co-existing fetus4.
An international consensus statement reported that CVS cells might not reflect the (epi)genetic constitution of the fetus, and therefore, false-positive results might occur5. Hence, amniocentesis is the more reliable investigation for imprinting disorders such as Beckwith-Wiedemann syndrome.
The criticism of over-simplification/generalisation is accepted. The intention was to state common associations and outcomes, not the exceptional ones.
Amarnath Bhide
Fetal Medicine Unit
St George’s University Hospitals NHS Foundation Trust
London