Placental Mesenchymal Dysplasia

Definition - What does Placental Mesenchymal Dysplasia mean?

Placental mesenchymal dysplasia (PMD) is an unusual abnormality in which the placenta and its villi reach an enormous size giving a false appearance of a molar pregnancy on examination. Placental villi are finger-like projections growing outwards from the placenta. PMD is a rare condition estimated to occur in about 0.02% of pregnancies. However, with the increasing awareness of this placental disorder, the true incidence may not be represented properly.

FertilitySmarts explains Placental Mesenchymal Dysplasia

PMD occurs when two sperm fertilize a single egg or when a single egg is fertilized by a single sperm, but with a failure of one or more pairs of chromosomes to separate normally during cell division.

The signs and symptoms of PMD may resemble a molar pregnancy and include:

  • Vaginal spotting or bleeding
  • Excessive nausea and vomiting
  • Preeclampsia (high blood pressure)
  • No fetal movement or heartbeat (if the baby dies in the uterus)
  • Features of elevated thyroid hormones

The levels of the pregnancy hormone, human chorionic gonadotropin (hCG) and another blood marker called alpha-fetoprotein (AFP) are raised. Given the raised thyroid hormone levels, the TSH levels are expected to be suppressed. An ultrasound reveals a grossly enlarged grape-like placenta with fluid-filled sacs that expand the villi. Its visual appearance may mimic that of a molar pregnancy. However, in PMD, the layer of cells that nourishes the developing embryo, called the trophoblast, do not appear to expand on ultrasound examination. In contrast, trophoblast proliferation is a common finding in molar pregnancy.

A chromosomal study called karyotyping can help differentiate placental mesenchymal dysplasia from a molar pregnancy. The number and size of chromosomes are usually normal in PMD versus the molar pregnancy where the karyotype is abnormal.

PMD tends to affect both the mother and baby. The enlarged placenta falls short of supplying nutrients and oxygen to the baby, interfering with its growth in the mother’s uterus. This growth restriction can be severe enough to cause fetal death inside the uterus.

If the pregnancy is viable, the baby may be born with one or more of the following potential complications of PMD:

  • Beckwith-Wiedemann syndrome (BWS). This is a genetic overgrowth disorder characterized by an abnormally large one side of the body, enlarged tongue, and various other facial and body defects.
  • Diabetes mellitus
  • Trisomy 13
  • Klinefelter syndrome
  • Premature delivery or delivery before term

Because it is possible that women with PMD can deliver a healthy baby, doctors usually do not advise termination of the pregnancy. The parents are, however, counseled against the associated risks.

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