Like an ectopic pregnancy, a molar pregnancy is also not viable. However, in a molar pregnancy, the implantation site is normal but the embryo is not. Called a hydatidiform mole, this placental tissue develops into a mass of cysts that are often described as resembling a cluster of grapes. There are two types of molar pregnancy, complete and incomplete (or partial).
A complete molar pregnancy occurs when an egg with no genetic material inside is fertilized by one or two sperm. Most have 46 chromosomes, all from the father (paternal). The pregnancy itself contains placental mass only and no embryonic tissue.
A partial molar pregnancy will usually contain some embryonic or fetal tissue. The majority of partial molar cases have two sets of paternal chromosomes and a single set of maternal chromosomes (69 in total).
Symptoms of molar pregnancy include:
Too small or too large uterus for date
Possible high hCG levels
Dark brown bleeding in the first trimester
Preeclampsia and toxemia
Ultrasound can make a diagnosis of molar pregnancy, which is estimated to occur in approximately one in 1,500 pregnancies in the United States. Older women have a higher risk for the condition, and the risk of subsequent molar pregnancy increases with each occurrence.
Risk of molar pregnancy is also influenced by geography. Although the incidence of the condition in the United States is relatively low, about one in 120 pregnancies in Southeastern Asia is molar. Several studies have also shown a higher incidence of molar pregnancy among women in the Philippines and Mexico. The exact reasons behind this phenomenon aren't completely understood, although genetic factors, diet, and environment have all been proposed as possible influences.
Removal by dilation and curettage (D & C) is the typical treatment for molar pregnancy. D & C is a surgical procedure involving dilating the cervix and suctioning the contents of the uterus. Synthetic hormones (oxytocin) may also be administered during the procedure to induce uterine contractions.
A molar pregnancy has the potential to develop into a rare type of cancer known as choriocarcinoma. A chest X-ray, bloodwork, and other radiological exams are done prior to D&C to determine if a molar pregnancy has metastasized (spread to other parts of the body).
Follow-up blood tests may be required for six months to a year afterwards to ensure that hCG levels have returned to normal. Levels that fail to return to normal or start to rise are an indication that persistent gestational trophoblastic disease (GTD) is present and further treatment is necessary. Rarely GTD may develop into choriocarcinoma. To accurately screen for these possibilities and ensure an early diagnosis, subsequent pregnancy should be avoided until the follow-up period is complete. Survival and remission rates are good if GTD is caught early and treated appropriately.