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Introduction

Twin pregnancy with CHMF (complete hydatidiform mole coexisting with a live fetus) resulting in a healthy take-home baby is rare, with only less than 60 cases documented in detail in literature. The estimated incidence is of one in 22,000–100,000 pregnancies [1], with most being complete hydatidiform moles (CHM) with a fetus; however, the reported prevalence for a partial mole with a coexisting fetus is 0.005–0.01% of pregnancies [2]. These cases are at high risk of spontaneous abortion, preterm delivery, intrauterine fetal death, antepartum bleeding, preeclampsia, persistent trophoblastic disease (PTD).

Case report

A 25-years-old female with complete mole and a coexistent live fetus detected on ultrasound at 18 weeks of gestation with a normal karyotype fetus on  amniocentesis at 20 weeks. The pregnancy was continued as per the patient’s desire and was closely monitored. At 30 weeks the patient had bleeding per vaginum for which emergency caesarean  section was performed and a live baby with a near normal Apgar score was delivered. The placenta with molar tissue was sent for histopathological examination. Her serum β hCG reached normal levels after delivery, and she is now on post-molar surveillance. The placenta with molar tissue was received in formalin. It had normal eccentric cord (19 cm, diameter of 0.6 to 0.1 cm) with three vessels. The cord had mild increase in coiling (6 twists) towards the left. There was normal presence of peri-arterial Wharton’s jelly. The disk (344 gm; fixed and trimmed; 16 × 12 × 4 cm) was roughly oval [Figure 1a]. The fetal surface is smooth, shiny with prominent vessels. Molar tissue [Figure 1a] was adherent to the placenta at one pole which was of size 12 × 12 × 3 cm composed of multiple grape like vesicles weighing 240 gm. The serial sections of placenta were unremarkable [Figure 1b]. On microscopy the sections from cord, membranes and disk were unremarkable. The molar tissue predominantly showed degenerative changes and was composed of villi [Figure 2a] which were diffusely edematous [Figure 2d, e] displaying cisterns and trophoblastic proliferation. The trophoblastic proliferation involved the entire circumference of the villi in molar tissue [Figure 2b, c]. 

Figure 1: (a) Placenta and molar tissue, (b) Serial sections of placenta.

Figure 2: (a) Low power view of  abnormal Villi, H&E 40x, [b, c] Villi with circumferential trophoblastic proliferation, H&E 100x, [d, e] Edematous villi.

Discussion

There are about less than 250 cases of complete mole with twin pregnancy documented in literature, and only less than 60 cases have resulted in live birth [3]. Vassilakos et al. based on cytogenetic analysis first described, partial and complete hydatidiform mole (CHM), which arise by different mechanisms [4]. Partial moles are derived from dispermic fertilization of a haploid normal oocyte and give rise to triploid set of chromosomes whereas CHM contains a diploid set of 46 paternally derived chromosomes, without any fetal parts. The fetuses are almost always triploid in partial moles and the indication for a termination of pregnancy is recommended. In contrast, the fetus may be normal in a twin pregnancy with a CHMF and continuation of pregnancy is commonly associated with maternal complications.

Ultrasonography is helpful in diagnosis of a hydatidiform mole with co-existent fetus in the first trimester [5]. Prenatal testing of the fetal karyotype is essential as it helps in deciding continuation and prognosis of the pregnancy. Termination of pregnancy is recommended in a triploid fetal karyotype and where as a diploid fetal karyotype is usually associated with a viable fetus with a normal placenta co-existing alongside a molar tissue as in this case, in which the pregnancy can be continued with close monitoring.

Usually partial mole associated fetuses are triploid but fetuses with normal karyotype also can occur in this setting.  The fetuses with partial mole are associated with asymmetrical intra uterine growth restriction (IUGR) and malformations [6]. Histopathological examination is important in distinguishing between the moles either by histopathology and/or with ancillary methods like p57 immunostain.  In the present case the features were compatible with complete mole, while clinically it was believed to be a partial mole.

Table 1 depicts the diagnostic features of moles which are helpful in distinguishing them from each other based on clinical and histopathological features [7]. Ancillary methods may be helpful in difficult situations. P57 which is paternally imprinted can be used in flow cytometry or immunohistochemistry for discriminating complete from partial moles [8].  Mesenchymal dysplasia and hydropic changes in the placenta can be diagnosed by clinical and the histopathological features.

Table 1: Depicts the diagnostic features of moles [7].

Abbreviations: CHM: complete hydatidiform mole; VECHM: very early complete hydatidiform mole; PHM: partial hydatidiform mole.

Prenatal diagnosis by amniocentesis as done in this case has been suggested to rule out triploidy or other genetic abnormalities, before continuation of a pregnancy [6].  Due to confined placental mosaicism there may be variation between fetal and placental karyotype is the reason why chorionic villous sampling is not recommended. The survival of the fetuses with complete mole are better than that of fetuses with partial mole [9] unless when it occurs in a dizygotic twin, with one fetus and the other oocyte giving rise to a partial diploid mole, however, abnormal fetus may result in  a monozygotic twin with triploidy giving rise to a partial mole [10]. In case of maternal complications like severe preeclampsia or bleeding one must be prepared for termination, and conservative management in these pregnancies puts the mother at risk of serious complications.

Steller et al. suggested that the risk of PTD is higher in cases of CHMF compared with single molar pregnancies and commonly progresses to metastatic disease [11] however Sebire and Niemann found out that the risk of PTD after CHMF is not significantly higher than in single molar pregnancies [12, 13].

Conclusion

A twin pregnancy with a complete mole and a coexisting live fetus requires a thorough evaluation, and pregnancy may be continued under close surveillance for an optimal outcome. Histopathological examination is essential for distinguishing between partial and complete mole and/or along with ancillary studies. Close follow-up is necessary during and after gestation to exclude persistent trophoblastic disease.

Conflicts of interest

There are no conflicts of interest.