Twin Pregnancies with co-existing complete hydatiform mole(CHM) and viable fetus Dr Lucas Luk, Dr Haris Suharjono, Dr Nicholas Ngeh Sarawak General Hospital, O&G Department. OPTIONAL LOGO HERE. OPTIONAL LOGO HERE.
Twin Pregnancies with co-existing complete hydatiform mole(CHM) and viable fetus
Dr Lucas Luk, Dr Haris Suharjono, Dr Nicholas NgehSarawak General Hospital, O&G Department
Distinguishing CHM in twin pregnancies from PHM in twin pregnancy is essential, as the former offers a much better possibility of a healthy newborn.
Generally, many are still uneasy about twin pregnancy with CHM and co-existing viable fetus, just like our patient. In documented twin pregnancies as such, ~50% opt for termination of pregnancy.1
The incidence of twin pregnancy with hydatidiform mole is 1 in 20 000 to 100 000 pregnancies.1,2 The majority of twin pregnancies involving a mole are those combining a Complete Hydatidiform Mole (CHM) and coexistent normal placenta and fetus.1,2 Twin pregnancies involving a Partial Hydatidiform Mole(PHM) and a coexistent normal gestational sac are rarely reported, while twin pregnancies where both fetuses are affected by PHM are exceptionally rare.1
Chorionic villus sampling with DNA polymorphism studies can be employed to determine the parental aetiology of the fetal chromosomes. This helps differentiate between CHM with co-existing normal twin and PHM in early pregnancy.1,4 The genotype of a CHM, in contrast to a PHM, is entirely of paternal origin. The diagnosis is made either by direct comparison with the paternal alleles when available, or by exclusion of the maternal alleles.1
With more women now deferring pregnancies till later in life, the risks of hydatidiform molar pregnancies is likely to increase. Older mothers are known to be at increased risk of problems during meiosis, due to poorer oocyte quality.3 Moreover, as in-vitro fertilization becomes a rising trend amongst women at the later stages of their reproductive life, the number of twin pregnancies with co-existing mole and viable fetus should increase.
This totally androgenous conceptus consists of a generalized swelling of the villous tissue, diffuse trophoblastic hyperplasia, giving rise to the classical ‘bunch of grape’ appearance on ultrasound, and no fetal or embryonic tissue.7
A classical mole may coexist with a normal fetus and placenta in cases of molar transformation of one ovum in a dizygotic dichorionic twin pregnancy and very rarely, in a monochorioinic one. CHM in a twin pregnancy will appear as a normal fetus and placenta next to a molar mass (vesicular sonographic pattern) on ultrasound scan.
Alternatively, if the co-existing fetus appears sonographically normal and pregnancy is pursued, determinations of allele inheritance can be performed after 15weeks through amniocentesis, or fetal blood sampling1. If the fetus is euploid it is suggestive of twin pregnancy with CHM and normal, viable fetus, rather than PHM. Provided the mother is clinically well, pregnancy may continue but she should be followed up fortnightly with serial ultrasound for growth assessment and cervical length monitoring to assess the risk of preterm labour.
We report a case of twin pregnancy with coexisting CHM, and a viable fetus. A 21 years old primigravida at 11 weeks gestation was referred to us for second opinion due to abnormal scan finding. Transabdominal scan demonstrated a normal fetus and placenta next to a mass, with vesicular pattern (Images 1 & 2). Diagnosis was viable fetus with coexisting molar pregnancy. The patient was counseled regarding the scan findings and possible management options. She elected for termination of pregnancy and subsequent histopathological report confirmed our diagnosis.
Women diagnosed with twin pregnancy with CHM and co-existing viable fetus should be referred to a maternal fetal unit for counseling and further management. In view of the multiple maternal and fetal risks involved, if continuation of pregnancy is desired, regular screening for possible maternal complications and assessment of fetal well-being should be performed.
An anticipated rise in the incidence of twin molar pregnancies with co-existing viable fetus can also be expected with the advent of molecular genetics and the progress of biochemical diagnostic tools. However, a high index of suspicion is still required to facilitate early diagnosis and appropriate management of such pregnancies.
Biochemical markers can be useful in diagnosing and distinguishing between singleton and twin CHM pregnancy:
Due to the influence of high maternal serum hCG, bilateral multicysticovaries are found in ~25% of patients with CHM pregnancies, as a result of theca lutein cystic transformation.
In 90% of PHM moles, the chromosome makeup is triploid: 2 paternal and one maternal, as a result of 2 sperm simultaneously entering an oocyte.4,5,7 Rarely, tetraploidy occurs. In PHM, there is a combination of a fetus with localized placental hydatidiform changes. Histologically, this is characterized by focal swelling of the villous tissue, focal trophoblastic hyperplasia and embryonic or fetal tissue.
In those continuing with pregnancy, there are increased maternal risks1,2,4 :
In the case of PHM in a twin pregnancy, 2 fetuses will be seen, one structurally normal and the other likely to show signs of growth restriction and structural anomalies. Ultrasound is an accurate diagnostic tool at the end of the first trimester.1,2 However, few reports of such pregnancies have been documented and fetal viability is poor.
However, current evidence suggests there is no increased risk of developing persistent trophoblastic disease(1/3) after carrying a twin CHM pregnancy to term, as compared to early termination. Outcome after chemotherapy is also unaffected.1,4
While uterine size is a prognosticator of PTD in a singleton molar pregnancy, the size of the mole does not appear to affect the development of PTD in twin molar pregnancies.3,4 Conversely, an increasing MShCG level and the presence of bilateral theca lutein cysts might indicate an increased risk of maternal complications including PTD.1 In this way, biochemical markers are useful in helping to manage molar pregnancies.
Complete molar pregnancies are diploid and androgenic in origin, with no evidence of fetal tissue.3-6 The chromosome count is usually (75-80%) 46XX, resulting from a single sperm duplicating within an empty oocyte.4 Occasionally (20-25%), a 46XY genotype can occur, when an empty ovum is fertilized by 2 sperm.4,7