Information for Patients with Molar Pregnancies or Choriocarcinoma
Introduction to Molar Pregnancy
Molar pregnancies are fairly rare, happening with roughly 1 case for every 600 pregnancies in the UK. When a molar pregnancy arises a problem occurs at the time of conception, when the egg and sperm join together, that results in the formation of cells that grow very rapidly but are unable to form the placenta and foetus of a normal pregnancy.
Molar pregnancies take two different forms, complete and partial molar pregnancies that differ in their genetic make-up, their development and in particularly in the risk of needing additional treatment.
The diagram in Fig 1 is a reminder of normally how an egg develops, is fertilised and then implants in the wall of the uterus. In a molar pregnancy the steps are identical except that at the time of fertilisation there is problem with either the maternal chromosomes being lost as in a complete mole or there being two sets of chromosomes from the father and one from the mother as in a partial molar pregnancy.
The diagram in Fig 2 shows the genetics of how the two different types of molar pregnancy arise and some of their important features. In a complete molar pregnancy the genetic material is just from the father as the original nucleus containing the mother's genetic material is lost at the time of conception or whilst the egg is developing in the ovary. Complete molar pregnancies form a mass of rapidly growing cells but do not contain a foetus and can not develop into a baby. After diagnosis and evacuation there is about a 10-15% chance of needing further treatment after a complete molar pregnancy.
In a partial molar pregnancy there is genetic material from both the father and the mother but an imbalance as there two sets from the father. In a partial molar pregnancy there can be a foetus visible on an early ultrasound, but it is always abnormal and can not develop into a baby as it does not survive beyond the first 3 months of the pregnancy.
After the evacuation, most partial molar pregnancies do not require any additional treatment as in more than 99% any of the residual cells just fade away over the next month or two.
In the first few weeks of a molar pregnancy there is often a tendency for morning sickness, bleeding and some abdominal pain. However these symptoms do not always occur and on their own are not particularly abnormal for a normal pregnancy. Most molar pregnancies are diagnosed at the first ultrasound scan that in a complete molar pregnancy shows a mass of cells without the presence of a foetus or in a partial mole an abnormal non-viable foetus and placenta. An ultrasound showing a complete molar pregnancy before evacuation is shown in Fig 3.