Fetoscopic Laser Photocoagulation for Twin-Twin Transfusion Syndrome in a Dizygotic Monochorionic Twins

To editor: Monochorionicity was traditionally considered indicative of monozygosity. However, recent years have witnessed the emergence of several noteworthy instances of monochorionic dizygotic (MCDZ) twins in clinical practice. In 2000, Viëtor et al.1 documented the initial established case of MCDZ twins. Subsequent studies have further documented this unconventional twinning phenomenon.2,3 The recognized complications associated with monochorionic monozygotic pregnancies, including twin-twin transfusion syndrome (TTTS), twin anemia–polycythemia sequence (TAPS), selective intrauterine growth restriction (sIUGR), congenital malformations, and intrauterine fetal death, could also manifest in MCDZ pregnancies.4,5 In this correspondence, we presented an extremely rare case of TTTS in a dizygotic monochorionic diamniotic twin gestation successfully treated with fetoscopic laser photocoagulation. The patients' permission to publish was obtained. Case presentation The presented case involves a 26-year-old, nulliparous woman who conceived through in vitro fertilization (IVF) due to polycystic ovary syndrome. The patient's oocytes were fertilized, and two resulting fresh embryos were subsequently transferred into the uterus. During the nuchal translucency (NT) scan, the identification of a T-shaped membrane insertion into the placenta indicated a monochorionic diamniotic twin gestation. The NT measurements of the two fetuses were 3.00 mm and 0.79 mm, respectively. Routine ultrasound assessments for fetal growth, amniotic fluid, middle cerebral artery (MCA), and umbilical artery were conducted every 2 weeks at the initial hospital starting from the 16th week of gestation. The patient was referred to our hospital at 23+5 gestational weeks due to discordant amniotic fluid. The maximum vertical pocket of amniotic fluid for the two fetuses was 35.00 mm and 87.00 mm, respectively, both exhibiting normal umbilical artery and MCA. The woman then underwent ultrasound scans 1 week later and returned at 25+6 gestational weeks for further evaluation, confirming the presence of TTTS stage 4. The donor twin showed an amniotic fluid maximum vertical pocket of 1.34 cm, whereas the recipient twin exhibited edema (pleural effusion and ascitic fluid) with a maximum vertical pocket of 13.62 cm. In addition, a significantly high pulsatility index of the umbilical artery and a negative A-wave in the ductus venosus were observed in the donor and recipient twin, respectively. After consulting with the patient's parents and obtaining signed informed consent, fetoscopic laser photocoagulation of vascular anastomoses was performed at 25+6 weeks of gestation. Under local anesthesia, as previously described,6,7 great vascular anastomoses (Fig. 1A & 1B) were identified and coagulated with 30-Watt laser power. The amniotic fluid returned to normal range on the 5th day after surgery, with a maximum vertical pocket of 6.40 cm and 4.20 cm, respectively, and both fetuses displayed normal fetal Doppler including umbilical artery, MCA, and ductus venosus.Figure 1: Great vascular anastomoses were identified (A, black arrow) and coagulated (B, black arrow) under the fetoscopy. The penis (C, white arrow) and clitoris (D, white arrow) were shown in the sagittal plane of prenatal ultrasound respectively. The recipient female showed overriding aorta (white arrow) and ventricular septal defect which indicated tetralogy of Fallot (E).At the same time, discordant fetal genitals were identified (Fig. 1C & 1D), and the recipient female showed ventricular septal defect and overriding aorta, indicative of tetralogy of Fallot (TOF) (Fig. 1E). No pathological variations were found in chromosomal microarray examination of both fetuses by amniocentesis. The patient delivered vaginally at 32+3 weeks of gestation due to premature rupture of membranes. The male donor twin weighed 1,815 g with Apgar scores of 8 and 9, whereas the female recipient twin weighed 1,740 g with Apgar scores of 8 and 9 at 1 and 5 minutes after birth. Both babies exhibited normal-appearing external genitalia. Histopathology of the placenta The placenta was obtained at delivery for a detailed histopathological analysis. Microscopic examination of the interamniotic membrane confirmed the monochorial status (Fig. 2A). Postdelivery, injection of color dye8 into placental vessels revealed a trace outlining the laser coagulation of the vascular anastomoses on the placental surface. A subtle demarcation at the placental equator was identified on a gross level (Fig. 2B and Video clips Supplementary, https://links.lww.com/MFM/A48).Figure 2: A Microscopic examination of the dividing membrane showed a monochorionic-diamniotic twin gestation: two layers of amnion consisting of epithelial cells and connective tissue without intervening chorion (black arrows). B Macroscopic examination of the single oval placenta: each individual anastomosis was identified and coagulated by fetoscopic laser, and the complete vascular equator (white arrows) is coagulated from one placental margin to the other.Cytogenic analyses G-banding karyotypes were conducted using cord blood obtained from the twins postdelivery. The karyotypes for both twins indicated a chimerism: 46,XY[94]/46,XX[6] for the male donor twin and 46, XY [94]/46, XX [6] for the female recipient twin. Molecular genetic analyses to assess zygosity A molecular genetic analysis was performed, involving DNA extraction from their umbilical cords postdelivery, and buccal cells were collected at 6 months of age. Polymerase chain reaction (PCR) tests were conducted using Platinum multiplex PCR master mix (Applied Biosystems, Waltham, MA, USA) with five highly polymorphic short tandem repeats AMXY, D2S1338, D21S11, D16S539, and D18S51. The results of these analyses confirmed dizygosity for the twins (Table 1). Table 1 - Molecular genetic zygosity testing using polymorphic short tandem repeats. Locus Map Twin A (Male Donor) Twin B (Female Recipient) Mother Father AMXY Xp22.2 104 109 104 104 104 104 104 109 D2S1338 2q35 168 176 168 180 168 176 168 180 D21S11 21q21.1 226 245 226 230 230 245 226 226 D16S539 16q24.1 150 162 162 162 150 162 150 162 D18S51 18q21.33 284 291 281 291 284 291 281 284 This analysis is consistent with dizygotic twinning and rules out monozygotic. Follow-up Peripheral blood chromosomal analyses through fluorescence in situ hybridization at 6 months of age revealed consistent findings. Blood chimerism levels remained at 46,XY[83]/46,XX[11] for the donor male twin and 46,XY[60]/46,XX[11] for the recipient female twin. Buccal smears at 6 months exhibited normal karyotypes for both fetuses, as confirmed by fluorescence in situ hybridization (46,XY and 46,XY of the 100 cells examined, respectively). At 1 month of age, the female infant underwent echocardiography, confirming the prenatal diagnosis of TOF. Successful surgical correction of TOF was performed at 10 months of age. Pediatric evaluation at 12 months of age revealed normal-appearing external genitalia and normal development milestones for both twins. Discussion It is conventionally accepted that monochorionic twins are monozygotic, whereas dizygotic twins consistently exhibit a dichorionic placenta. The identification of MCDZ cases has been found accidentally and reported in case studies, initially considered rare occurrences. However, with the development of artificial reproductive technology (ART), an increasing number of MCDZ cases have been documented.9,10 MCDZ twins may not be rare as previously reported; however, their prevalence might be underestimated due to the limited knowledge of this twin type. A Danish study, involving 495 twins with known chorionic and zygotic types, indicated that 5.4% (4/74) of MCDA cases were MCDZ twins.11 The incidence of MCDZ was even higher in twin pregnancy conceived through ART. Another study, employing single nucleotide polymorphism arrays to confirm zygosity in 24 MC twins conceived through ART, revealed that 12.5% (3/24) of MCDA conceived by ART were identified as MCDZ.12 To date, 40 MCDZ twins have been reported, with 39 cases documented in PubMed and the case presented in this study. Cases of MCDZ gestations complicated by TTTS were rarely reported. To the best of our known, only eight cases (including the current case) complicated by TTTS2,12–17 have been reported. Table 2 summarizes the basic characteristics of these cases. In seven of eight cases, the method of conception was documented, with ART identified as a significant etiological factor in 57.1% (4/7) of the cases, which mainly were conceived after IVF/intracytoplasmic sperm injection treatment. In the five cases with discordant gender, two pairs shared the same gender. Dizygosity in the two pairs of same-gender twins was discovered as in one case; one of the twins developed bilateral retinoblastoma at 7 months of age, and in the other case, the parents required for zygosity testing because of significant discordant facial features in the twins at 14 months of age. In seven of eight cases, the TTTS stage was detailed, ranging from stage 1 to stage 4 (current case). In one case, acute TTTS was reported at delivery, resulting in the demise of the male twin. Among the four TTTS cases undergoing laser therapy, three resulted in live births, whereas one case suffered from miscarriage due to premature rupture of membranes postoperation. Table 2 - Review of the dizygotic monochorionic twin pregnancies with twin-twin transfusion syndrome reported in the literature including the current case. Case Maternal age (years) Conception TTTS stage Laser treatment Pregnancy outcome Chimerism Karyotypes Follow-up Quintero et al. (2003)2 28 NA Stage 1 Yes Miscarriage in the 2nd trimester NA Female: 46,XXMale: 46,XY NA Ekelund et al. (2008)13 38 ICSI Stage 1 No Alive, CS at 32 weeks Blood (+)Buccal cells (−) Female: 46,XX[6]/46,XY[6]Male: 46,XX[5]/46,XY[6] 6 months Assaf et al. (2010)12 28 ICSI Stage 1 Yes Alive, CS at 37+4 weeks Blood (+)Buccal cells (−) Female: 46,XX[73]/46,XY[27]Male: 46,XX[32]/46,XY[28] 28 months Loriaux et al. (2011)14 30 Natural Acute TTTS at delivery No One IUFD boy, another alive, VD at 29+5 weeks Blood (+)Skin (−) Female: 46,XX[31]/46,XY[69]Male: NA 3 years Umstad et al. (2012)15 36 Natural Stage 1 No Alive, CS at 36 weeks Blood (+)Buccal cells (−) Both females 14 months Armitage et al. (2020)16 NA Natural NA No Alive, CS at 35 weeks Blood (+)Skin (+) RB1 variation 7 months Chang et al. (2021)17 49 ICSI Stage 1 Yes Alive, CS at 29 weeks Blood (+)Buccal cells (−) Female: 46,XX[9]/46,XY[41]Male: 46,XX[4]/46,XY[46] 6 weeks Current case report 26 IVF Stage 4 Yes Alive, VD at 32+3 weeks Blood (+)Buccal cells (−) Female: 46,XX[11]/46,XY [60]Male: 46,XX[11]/46,XY[83] 11 months CS: Cesarean section; ICSI: Intracytoplasmic sperm injection; IUFD: Intrauterine fetal demise; IVF: In vitro fertilization; NA: Not available; TTTS: Twin-twin transfusion syndrome; VD: Vaginal delivery. The confined blood chimerism was noted in the majority of the MCDZ twins, which is resulting from intrauterine blood sharing via the placental vascular anastomoses.18,19 In MCDZ cases complicated with TTTS, the degree of blood chimerism appears to be higher, potentially related to the pathophysiology of TTTS, which manifests an imbalance in vascular communication between twins, with the donor twin transfusing more blood to the recipient twin. Assaf et al.12 reported an MCDZ case complicated by TTTS stage 1, demonstrating a higher blood chimerism in the recipient twin compared with the donor twin (53%–70% vs. 18%–27%, P < 0.01). In our case (TTTS stage 4), a significantly higher degree of blood chimerism was also observed in the recipient fetus compared with the donor fetus (94% vs. 6%). To be noted, compared with the other reported cases of TTTS in stage 1, the degree of chimerism in our case was significantly higher. Although we speculate that the degree of blood chimerism may be associated with the stage of TTTS, further confirmation through additional cases is needed. Monochorionic twin pregnancies have been associated with higher perinatal mortality and morbidity compared with dichorionic twin pregnancies. The risk of TTTS in MCDZ twin pregnancies appears to be comparable to that in monochorionic pregnancies reported previously.3 Based on our review, 20% of MCDZ twins (8/40) were complicated by TTTS, aligning with the prevalence (10%–20%) of TTTS in monochorionic pregnancies.11,20 Conclusion In conclusion, we present a case of MCDZ twins developing TTTS, successfully treated with fetoscopic laser therapy. The important clinic implication was that we should consider the possibility of MCDZ twins, especially in monochorionic twin pregnancies with different fetal genders and those conceived with ART. Early determination of chorionicity during the first trimester is important to promptly and accurately identify MCDZ twins, especially given their similar prevalence of complications unique to monochorionic twin pregnancies such as TTTS.