Chapter 18: The Female Reproductive Tract
A 38-year-old woman with a history of prior spontaneous abortion presents during her 10th week of pregnancy. She is found to have a larger than expected uterus size for estimated gestational age. Diagnostic workup shows that her serum hCG is greatly elevated. A pelvic ultrasound is ordered and reveals an abnormal gestation, with a “snowstorm” appearance of the uterus without an identifiable gestational sac. A uterine dilation and curettage (D&C) is performed and the uterine contents are diffusely edematous chorionic villi, without an identifiable fetus, as shown in the accompanying gross pathology image (Figure 18-54). What is the most likely karyotype of this condition?
B. Diparental diploid 46, XY
C. Dipaternal diploid 46, XX
D. Dimaternal diploid 46, XX
Explanation: The clinical vignette is most consistent with a complete hydatidiform molar pregnancy. The risk factors for hydatidiform moles are extremes of maternal age (<20 and >35 years old), and a prior history of a hydatidiform mole, infertility, or multiple miscarriages. The clinical symptoms include rapid increase in uterine size, abnormal vaginal bleeding, and hyperemesis gravidarum. Some women may have symptoms of hyperthyroidism because of the homology between hCG and thyroid-stimulation hormone (TSH). The diagnostic workup includes blood hCG which is typically markedly elevated (>100,000 mIU/mL) and a pelvic ultrasound which shows an enlarged uterus size for expected gestational age, a “snowstorm” pattern of the uterus due to the grossly hydropic abnormal chorionic villi, and absence of an embryo. Complete hydatidiform mole is of dipaternal origin and the possible mechanisms are (1) duplication of a paternal set of chromosomes that fertilize an empty ovum (46, XX, most common), or (2) fertilization of an empty ovum by two separate sperm (either 46, XX or 46, XY). The initial management of a complete mole is uterine D&C. The histology shows abnormal chorionic villi with hydropic cisterns, trophoblastic proliferation, and atypia. No fetal tissue is present. Patients with complete moles have a high risk of progression to gestational trophoblastic neoplasia (15–20%) including invasive moles and malignancies such as choriocarcinoma (2–5%). Therefore, patients require close clinical follow-up with physical exam, radiology, and hCG levels after initial uterine evacuation.
Answers A and E are karyotypes of a partial hydatidiform mole. Partial hydatidiform moles are triploid, with one set of maternal chromosomes and two sets of paternal chromosomes. The possible mechanisms of partial moles are (1) duplication of a paternal set of chromosomes that fertilizes a normal haploid ovum (69, XXX), (2) fertilization of a normal haploid ovum ...