Review Question - QID 107026

The pregnant female has a benign placental tumor called a hydatidiform mole. In this case, it is a complete mole due to an empty ovum fertilized by two sperm.

The most likely cause of a complete mole is an empty ovum fertilized by 1 sperm that duplicates its DNA though it is still possible though less likely for 2 separate sperm to fertilize 1 empty ovum. A hydatidiform mole is a benign placental tumor that results in swelling of chorionic villi and trophoblastic proliferation. They are more common in women of Asian descent. Moles can be of two types: complete, the most common, or partial. A complete mole is a consequence of an empty ovum being fertilized by the entry of 2 sperm, resulting in a karyotype of 46 XX or XY, with all chromosomes being of paternal origin and no fetus present. More commonly, an empty ovum will be fertilized by one sperm with subsequent duplication of the sperm producing a karyotype of 46,XX or 46YY. A partial mole is a consequence of an ovum being penetrated by two sperm, resulting in a karyotype of 69 XXX or XXY, where 46 chromosomes are of paternal origin and 23 are maternal. In partial moles fetal tissue is present.

Figure A shows a transvaginal ultrasound of a molar pregnancy demonstrating the characteristic 'cluster of grapes' appearance of the hydatidiform mole. Illustration A is an H&E staining of a hydatidiform mole, showing areas of trophoblastic proliferation with large avascular villi.

Incorrect Answers:
Answer 1: An ectopic pregnancy is a result of a fertilized egg (one sperm and one ovum) implanting in an area other than the uterus, such as the fallopian tubes. It is common for ectopic pregnancies to rupture. If an ectopic pregnancy is suspected a beta-hCG and transvaginal ultrasound should be performed to confirm a pregnancy and its location.

Answer 2: A fertilized egg implanting in the uterus is a normal pregnancy.

Answer 3: An ovum fertilized by two sperm would produce a karyotype of either 69,XXX, 69,XXY, or 69, XYY. which is a partial mole. Partial moles will actually form fetal tissue.

Answer 4: An ovum fertilized by one sperm with subsequent duplication would produce a 69,XXX or 69,XYY.

Bullet Summary:
A complete mole occurs when an empty ovum is fertilized by:
1. 1 sperm that duplicates
2. 2 different sperm (less likely)