Normal Co-twin Research Articles

Use of holmium laser for umbilical cord transection in a monoamniotic pregnancy threatened by an acardiac co-twin: a case report

BackgroundTwin reversed arterial perfusion sequence is a rare complication of monochorionic multifetal pregnancies. In this syndrome, the acardiac twin has a nonfunctional heart, while the other twin, the pump twin, has normal development. The pump twin perfuses the acardiac twin and is therefore at risk for cardiac decompensation. In monoamniotic cases, the normal co-twin is also at risk of sudden death due to cord entanglement. Treatment consists of coagulation and transection of the acardiac’s umbilical cord. We report the first intrauterine use in pregnancy of a Ho:yttrium aluminum garnet laser to safely and successfully transect the umbilical cord after Nd:yttrium aluminum garnet coagulation.Case presentationA 30-year-old Caucasian woman was referred to our fetal–maternal medicine unit at 9 weeks gestation with a monochorionic–monoamniotic twin pregnancy complicated by an acardiac twin. After counseling, she opted for an elective intervention to minimize the risks to the pump twin. At 16 weeks, fetoscopy was performed using a single 2-mm entry port. Through this port, a 1.0-mm fetoscope and a 0.365-mm laser fiber were introduced. Under fetoscopic sight and ultrasound (Doppler) guidance, the umbilical cord of the acardiac twin was first coagulated by laser energy using a Nd:yttrium aluminum garnet laser and then, using the same fiber, transected using a Ho:yttrium aluminum garnet laser. The patient underwent cesarean section at 38 weeks and delivered a healthy baby.ConclusionsWe present the first report on intrauterine use of an Ho:yttrium aluminum garnet laser in human pregnancy. Ho:yttrium aluminum garnet laser energy can be successfully and safely used for umbilical cord transection and carries fewer risks than other methods of transection.

Integration of imaging and molecular approaches in selective fetal reduction in twin pregnancies with one carrying a pathogenic genomic aberration

With the evolution of assisted fertility and prenatal diagnostic technology, the prevalence of multi-fetal pregnancy increased, followed by the demand for prenatal intervention if genomic aberration was detected. How to distinguish the affected foetus from the normal co-twin before selective fetal reduction is therefore challenging. We retrospectively reviewed the cases of dichorionic twins at our centre during 2004-2018, where selective fetal reduction was requested because one foetus carried a pathogenic genomic aberration. Five cases were enrolled, including three foetuses with trisomy 21, one foetus with microduplication and one foetus with microdeletion disorders. We labelled the affected foetus by prenatal ultrasound and rapid molecular tools. For the twins without discriminating sonographic features (e.g., the same gender and no distinct placentae), interphase fluorescence in situ hybridization, rapid microarray and short tandem repeat markers were applied to identify the affected foetus. Selective fetal reduction was allocated accurately for all individuals. Two cases delivered at term, while two delivered preterm, and one developed fetal loss of the co-twin. We proposed a working scheme of integrating imaging and molecular techniques to correctly identify the affected co-twin before selective fetal reduction to ensure the accuracy of the identification.

Major Discordant Structural Anomalies in Monochorionic Twins: Spectrum and Outcomes

Monochorionic twins, resulting from a single fertilized egg giving rise to two separate embryos, are monozygotic and considered genetically identical. However, discordant phenotypes have been reported in monozygotic twins. We analyzed a retrospective cohort of 155 monochorionic pregnancies (312 twins) with major discordant structural anomalies coded by the ICD-10 system in order to describe the spectrum of anomalies, the management of the pregnancies, and the perinatal outcome. Treatment options included conservative management, selective feticide with bipolar cord coagulation, or complete termination. All survivors underwent at least 24 months of postnatal follow-up. Discordancy was complicated by twin-to-twin transfusion syndrome in eight pregnancies (5%) and by selective intrauterine growth restriction in 41 (26%). Major structural anomalies affected one system in 139 cases (90%) and multiple systems in 16 (10%). Median gestational age at diagnosis was 19.1 weeks (IQR 16.4-21.3). The most frequent single-system anomalies involved the nervous and circulatory systems. In total, 72 anomalous twins (46%) and 116 normal co-twins (74%) were delivered at a median gestational age of 34.6 weeks (IQR 31.0-36.3). Neonatal/infant death of the anomalous twin occurred in 22 cases (14%), with an overall survival rate of 32% (50/155). Surviving anomalous twins underwent major surgery in 22/50 cases (44%), four of whom (8%) now suffer from severe neurologic morbidity. This study shows that a wide spectrum of major discordant structural anomalies can be found in monochorionic pregnancies. The outcome for the anomalous twin is poor, while the survival rate for the normal co-twin was 71%, with a favorable overall prognosis.

Twin pregnancy complicated by esophageal atresia, duodenal atresia, gastric perforation, and hypoplastic left heart structures in one twin: a case report and review of the literature

BackgroundThe antenatal diagnosis of a combined esophageal atresia without tracheoesophageal fistula and duodenal atresia with or without gastric perforation is a rare occurrence. These diagnoses are difficult and can be suspected on ultrasound by nonspecific findings including a small stomach and polyhydramnios. Fetal magnetic resonance imaging adds significant anatomical detail and can aid in the diagnosis of these complicated cases. Upon an extensive literature review, there are no reports documenting these combined findings in a twin pregnancy. Therefore we believe this is the first case report of an antenatal diagnosis of combined pure esophageal and duodenal atresia in a twin gestation.Case presentationWe present a case of a 30-year-old G1P0 white woman at 22-week gestation with a monochorionic-diamniotic twin pregnancy discordant for esophageal atresia, duodenal atresia with gastric perforation, hypoplastic left heart structures, and significant early gestation maternal polyhydramnios. In this case, fetal magnetic resonance imaging was able to depict additional findings including area of gastric wall rupture, hiatal hernia, dilation of the distal esophagus, and area of duodenal obstruction and thus facilitated the proper diagnosis. After extensive counseling at our multidisciplinary team meeting, the parents elected to proceed with radiofrequency ablation of the anomalous twin to maximize the survival of the normal co-twin. The procedure was performed successfully with complete cessation of flow in the umbilical artery and complete cardiac standstill in the anomalous twin with no detrimental effects on the healthy co-twin.ConclusionsPrenatal diagnosis of complex anomalies in twin pregnancies constitutes a multitude of ethical, religious, and cultural factors that come into play in the management of these cases. Fetal magnetic resonance imaging provides detailed valuable information that can assist in management options including possible prenatal intervention. The combination of a cystic structure with peristalsis-like movement above the diaphragm (for example, “the upper thoracic pouch sign”), polyhydramnios, and progressive distention of the stomach and duodenum should increase suspicion for a combined pure esophageal and duodenal atresia.

Acardiac Acephalus Twin Pregnancy with Poor Prenatal Outcomes: A Case Report

Introduction: Acardiac twin refers to a monochorionic pregnancy in which there is a twin with absent or nonfunctioning heart and a normal co-twin. This was a very rare disorder of monozygotic twin pregnancy. The aim of this report was to introduce a case of acardiac acephalus twin pregnancy. Case Presentation: A 32- year- old woman (G3 P2 L2) referred to the hospital because of a decrease in fetal movement at 32 weeks of gestation. Ultrasonography showed a dead fetus. Her earlier sonography showed the possibility of acardiac twin pregnancy, but she did not have any appropriate or special prenatal care for this problem. After delivery, there was a normal dead fetus without any gross abnormality and another acardiac fetus. Conclusions: Early diagnosis of acardiac twin pregnancy and appropriate prenatal care are of prime importance for appropriate intervention and best fetal outcomes.

Fetal Anomalies in Twin Pregnancies

ABSTRACT Twinning increases the chances of structural anomaly in the fetus. Discordance in physical development of the fetuses raises both ethical and management dilemma. Chorionicity plays an important role when selective feticide is an option. Anomalies found in singleton pregnancy can also be found in twins. Certain anomalies, such as acardiac fetus, are unique to monochorionic (MC) twin gestations. These anomalies may require in utero intervention to salvage its normal co-twin. Structural abnormalities, such as obstruction in fetal gastrointestinal tract resulting in polyhydramnios, can threaten the loss of the whole pregnancy. In MC twins, demise of the anomalous fetus can result in either demise or cerebral palsy of its co-twin. Fetal cord occlusion of the anomalous fetus can be offered to prevent these deleterious effects to its normal co-twin. Discordance of karyotypes in dichorionic (DC) twins is increasingly diagnosed in prenatal period. Selective feticide in this situation is simpler, but more ethical concerns are being raised. The technical and ethical considerations related to various kinds of discordance fetal malformations in the twin pair will be discussed in this review article. How to cite this article Wataganara T, Nawapun K, Phithakwatchara N. Fetal Anomalies in Twin Pregnancies. Donald School J Ultrasound Obstet Gynecol 2016;10(3):308-312.

Perinatal Outcome of Discordant Anomalous Twins: A Single-Center Experience in a Developing Country.

A dramatic increase in twin pregnancies has been observed in the past few decades, primarily related to assisted reproductive techniques (ART) and increased average maternal age during pregnancy. Multiple pregnancies, compared to singleton pregnancies, are associated with greater perinatal morbidity and mortality. The present study evaluated the perinatal outcomes of pregnancies with discordant anomalous twins in a tertiary maternity ward in a developing country. Data were retrospectively collected from the Instituto Fernandes Figueira/FIOCRUZ, Brazil between January 2002 and December 2014. We identified 74 twin pregnancies with discordant anomalous twins. Final data analysis was based on 40 pregnancies. Congenital defects were classified according to the International Classification of Diseases: ICD-10: the digestive system was responsible in 27 (34%) cases; the central nervous system was responsible in 18 (22%) cases; the urinary tract was responsible in 14 (17%) cases; and the circulatory system was responsible in 14 (17%) cases. A total of 19 deaths occurred during the study period, and delivery before 30.4 weeks was a significant prediction of fetal death (p = .01). The presence of hydrops in the affected fetus was related to a higher number of deaths in healthy fetuses and contributed to a worse prognosis. The presence of this condition was the cause of 12 (55.6%) deaths in healthy fetuses. A 10 times higher risk of death of a normal co-twin was observed in cases of death of the anomalous twin (p = .002, OR 10.55, 95% CI: 1.9-58.52).

Diagnosis and Management of Complicated Monochorionic Twins.

Although monochorionic (MC) twins comprise only 20% of all twin pregnancies, the risk for fetal loss and long-term morbidity is significantly higher than dichorionic twins due to the presence of placental vascular anastomoses. MC twins are at risk for multiple unique complications including twin-twin transfusion syndrome, selective intrauterine growth restriction, twin anemia-polycythemia sequence, and twin reversed arterial perfusion sequence. Discordant anomalies can negatively impact the outcome for the normal cotwin. It is imperative that early determination of chorionicity is established such that the appropriate surveillance is in place to identify MC complications to optimize outcomes.

Pregnancy prognosis associated with an isolated single umbilical artery in twin pregnancy.

To determine the prognosis of an isolated single umbilical artery (SUA) in a twin pregnancy, we selected twin pregnancies with a second trimester ultrasound diagnosing a SUA in at least one fetus at our tertiary hospital. This was confirmed by placental histopathology or by expert review of ultrasound images. Cases were identified by searching the hospital ultrasound database over a period of 7.5 years. Higher order multiples or coexistent aneuploidy or major anomalies were excluded. Each case of an isolated SUA was assigned three consecutive twin pregnancy controls paired for chorionicity and maternal age. Primary outcomes were preterm birth <34 weeks, small for gestational age (SGA) or perinatal death. Other outcomes included antenatal growth restriction, mode of delivery, and admission to neonatal intensive care or special care nursery. Nine pregnancies (18 fetuses) were identified for analysis as cases. Isolated SUA was associated with preterm birth <34 weeks (odds ratio = 12.2; 95% CI = 2.0-75.2; p = .005) but not for SGA. There was also no difference in SGA between the affected twin and its normal co-twin. Perinatal death was increased but after controlling for gestational age and clustering this finding was no longer significant. We conclude that isolated SUA in twins adds a degree of risk to an already high-risk pregnancy but does not increase the need for surveillance for growth restriction.

Prediction of intrauterine death and severe preterm delivery in twin pregnancies discordant for major fetal abnormality

ObjectiveTo investigate predictors of spontaneous fetal death and preterm delivery in twin pregnancies with one fetus affected by a major structural malformation. Study designRetrospective study (1999–2012) conducted at a tertiary teaching hospital involving 51 twin pregnancies (dichorionic=31, monochorionic diamniotic=15, monochorionic monoamniotic=4, not established=1) with a major fetal abnormality, enrolled before 26 weeks and managed expectantly. Primary outcomes: spontaneous fetal death, and/or delivery before 32 weeks. Prediction was examined with stepwise logistic regression analysis, and independent variables included: maternal age, gestational age at diagnosis, chorionicity, fetal gender, number and type of fetal abnormalities. Significance level was set at 0.15. ResultsFetal abnormalities were diagnosed at a mean gestation of 21.5±3.7 weeks: cardiac abnormalities were observed in 31.4% of abnormal fetuses, abdominal wall defects in 29.4%, central nervous system 21.5%, spine 17.6%, effusions 17.6%, noncardiac thoracic abnormalities 15.7%, genital and urinary system 13.7%, limbs and soft tissue 3.9%, intestinal 1.9% and facial defects 1.9%. Fetal death occurred in 15 (29.4%) abnormal fetuses and was significantly correlated with the number of fetal malformations (p=0.02, OR=2.54, 95% CI=1.14–5.62), presence of effusion/hydrops (p=0.06, OR=4.7, 95% CI=0.95–24) and monochorionic placenta (p=0.11, OR=2.8, 95% CI=0.78–9.8). Normal co-twin fetal death occurred in four cases (7.8%) and was related to monochorionic pregnancies (p=0.14, OR=5.8, 95% CI=0.56–61). Delivery before 32 weeks was observed in 14 (27.5%) pregnancies and was related to presence of effusion/hydrops (p=0.04, OR=5.5, 95% CI=1.07–28). ConclusionSpontaneous fetal death and/or delivery before 32 weeks in twin pregnancies with one fetus affected by a major structural malformation are related to the number of abnormalities diagnosed and presence of fetal effusion or hydrops.

The Outcome of Twin Pregnancies Discordant for Trisomy 21

The management of twin pregnancies discordant for trisomy 21 is dependent on the gestation at diagnosis, chorionicity, and parental preference. Our experience with the management of 15 cases in 1,839 twin pregnancies over a 12-year period is described. Selective termination is not always associated with a successful outcome for the normal co-twin. Two of the three monochorionic twin pregnancies affected by trisomy 21 were discordant. Amniocentesis should be strongly considered rather than chorionic villus sampling in monochorionic twin pregnancies. Pregnancies that continue with a trisomy 21 affected fetus are at risk of polyhydramnios and premature labor.

Placental endoglin levels in diamniotic-monochorionic twin gestations: Correlation with clinical and placental characteristics

ObjectiveWhile endoglin has been implicated in the pathogenesis of various complications in singleton pregnancies, its potential contribution to complications of monochorionic twinning remains largely undetermined. The aim of this study was to determine the correlation between relevant clinical and pathological variables and placental endoglin levels in diamniotic-monochorionic twin pregnancies. MethodsEndoglin expression was studied by immunohistochemistry and Western blot in a prospective cohort of 68 non-TTTS and 7 TTTS monochorionic twin placentas. Placental endoglin levels were correlated with clinical and placental characteristics associated with twin-to-twin transfusion syndrome (TTTS) and selective growth restriction, including birth weight discordance, uneven placental sharing, peripheral cord insertion and choriovascular anatomy. ResultsIn non-TTTS gestations discordant for these criteria, placental endoglin levels were significantly higher for the twin with smaller birth weight, intrauterine growth restriction, and/or abnormal ultrasound Doppler studies than for the more normal co-twin. Similarly, placental endoglin levels were significantly higher in the placental territory with smaller share and/or peripheral cord insertion in cases discordant for these placental characteristics. In TTTS gestations, placental endoglin levels tended to be higher for donor twins than for recipients. There was no correlation between endoglin levels and superficial choriovascular anastomoses. ConclusionsWhile the exact functional implications remain to be determined, our findings suggest a strong correlation between unbalanced placental endoglin levels and intertwin growth discordance in monochorionic twins.

169: Are twin to twin transfusion syndrome and selective intra-uterine growth restriction a continuum? Evidence from a longitudinal study of circulating angiogenic factors

intra-uterine growth restriction a continuum? Evidence from a longitudinal study of circulating angiogenic factors Yoav Yinon, Elad Ben Meir, Boaz Weisz, Eyal Schiff, Shali Mazaki-Tovi, Shlomo Lipitz Sheba Medical Center, Tel-Aviv University, Obstetrics and Gynecology, TelHashomer, Israel OBJECTIVE: To determine maternal plasma levels of soluble fms-like tyrosine kinase-1(sFlt-1), placental growth factor (PLGF) and soluble endoglin (sEng) in monochorionic diamniotic (MC/DA) twin pregnancies complicated by twin to twin transfusion syndrome (TTTS) or selective intra-uterine growth restriction (sIUGR). STUDY DESIGN: A longitudinal cohort study of pregnant women with MC/DA twins who were classified into 3 groups: 1. Uncomplicated MC/DA twins (n 22) 2. TTTS (n 23) and 3. sIUGR (n 15). Maternal plasma samples were obtained between 13-20 and 21-28 weeks of gestation and cord blood samples were collected at delivery. Maternal plasma concentrations of sFlt-1, PLGF and sEng were measured by ELISA. RESULTS: sFlt-1 and sEng levels were significantly higher in TTTS at the early (13-20 weeks) and late (21-28 weeks) second trimester compared to normal monochorionic pregnancies (p 0.01). In contrast, sFlt-1 and sEng levels were significantly higher in the sIUGR group only at the late second trimester (p 0.05). PLGF levels were significantly lower at the early and late second trimester in both TTTS and sIUGR compared to controls (p 0.01). Plasma concentrations of sFlt-1 were significantly higher among TTTS pregnancies compared to sIUGR at the late second trimester (p 0.027). Within TTTS pregnancies who underwent fetoscopic laser ablation, the procedure resulted in elevation of PLGF levels and reduction of sFlt-1 levels. Cord blood analysis revealed significantly higher levels of sFlt-1 in the smaller IUGR twin compared to the normal co-twin. CONCLUSION: Monochorionic pregnancies complicated by TTTS and sIUGR are characterized by decreased angiogenic activity. The disparity in severity of the anti-angiogenic state between TTTS and sIUGR suggests that these two conditions may represent a continuum. Collectively, the findings reported herein shed new light on the pathophysiologic mechanisms of these severe complications of pregnancy.

P31.11: Complete hydatidiform mole and normal live birth: placental mosaicism or twin with CHM?

Introduction: survival of a normal fetus to term in the presence of hydatidiform mole remains an extremely uncommon occurrence. Prenatal diagnosis is possible by ultrasonography showing molar invasion of the normal placenta without clear margin. Antenatal detection of mole co existing with a viable fetus should warrant genetic analysis and search for gross malformation of the fetus. Case report: we report a rare case exhibiting molar pregnancy and a coexisting normal fetus. A 29 year, primigravida had an episode of vaginal bleeding at 18 weeks which suggested avascular lower placenta with multiple cystic area measuring 12 × 5 × 9 cm with normal fetus. She had two weekly growth scan and Doppler as diagnosis was not clear. It was thought to be multiple placental lakes. Growth and Doppler remains normal and had term SVD. Placenta was sent for histopathology which suggested normal placenta with an area of complete hydatidiform mole. It was difficult to differentiate from mosaic CHM, twin with normal co-twin and CHM. Discussion: coexistent live fetus and molar placenta has never been reported. Complications including pre-eclampsia, hyperthyroidism, vaginal bleeding, persistent gestational trophoblastic disease, preterm labour, miscarriage and anaemia increases. Several factors may influence the outcome in partial mole such as karyotype of the fetus, size of the molar placenta, the speed of molar degeneration and fetal anaemia.

Secuencia TRAP: diagnóstico, opciones de tratamiento y experiencia propia

Twin reversed arterial perfusion syndrome or TRAP sequence is a rare and exclusive complication of monochorionic pregnancies. It is characterized by the presence of a malformed fetus whose heart is rudimentary or absent, and has no direct placental perfusion, but its blood flow is coming through a direct A-A (A-A) comunication from the structurally normal co-twin, (pump twin), and then after perfusing to the acardiac one, double deoxygenated blood returns to the pump twin through a veno-venous connection (V-V).The natural history of the disease is death from heart failure of the pump twin in 35-55% of the cases.The purpose of this paper is to review the basics aspect and the current status of this condition, focusing primarily on diagnosis, management options, prenatal invasive treatment alternatives, and to present a review of our experience.

Radiofrequency ablation as a minimally invasive procedure in the treatment of twin reversed arterial perfusion sequence in twin pregnancy

Twin reversed arterial perfusion sequence is a rare anomaly of monochorionic multiple pregnancies affecting 1 of 35,000 pregnancies and 1% of monochorionic twin pregnancies. In this condition the affected twin has lethal malformations including poor or absent heart development and is reversely perfused by a structurally normal co-twin. We report a case of a 21-year-old woman with a monochorionic twin pregnancy affected by twin reversed arterial perfusion sequence. This case highlights the therapeutic options and the management by radiofrequency ablation, which has been shown to be an easy and reliable technique with a high success rate compared with technically demanding fetoscopic procedures.

Dichorionic twin pregnancy discordant for fetal anencephaly: a case report

Dichorionic twin pregnancy discordant for fetal anencephaly is a serious condition that threatens the normal co-twin's life by causing polyhydramniosis, preterm labor and sudden death of one or both of the fetuses. We report a case of dichorionic twin pregnancy discordant for fetal anencephaly delivered at the 32(nd) week of gestation because of preterm labor and nonreassuring fetal monitoring. The aim of this case report is to summarize management options in this situation.

Advances in Ultrasonic Assessment of Acardiac Twin

ABSTRACT The development of an acardiac anomaly, one of the most severe human malformations, is a rare complication unique to monochorionic multiple pregnancies. In this condition, the primary malformation is the lack of a well-defined cardiac structure in one twin (the acardiac twin), which is kept alive by its structurally normal co-twin (the pump twin). The final diagnosis for a twin pregnancy with an acardiac twin may be established after the 9th week, when the cephalic extremity and limbs can be precisely determined. Direct signs that lead to the diagnosis of an acardiac twin include the absence of cardiac and fetal movements, difficult visualization of the trunk and cephalic poles, thickening of subcutaneous tissue and the presence of umbilical artery reverse flow towards the acardiac fetus mass. The pump fetus may demonstrate hydramnios, cardiomegaly and heart failure. Once an acardiac anomaly is diagnosed, both the acardiac and pump twins should be assessed to classify the pregnancy according to prognostic factors based on the size and growth of the acardiac twin and the cardiovascular condition of the pump twin. Assessing the extent of heart damage in the pump fetus is a key step in pregnancy management. There are two available options, either conservative or interventional, for the management of these pregnancies. Serial ultrasound surveillance is important for detecting any worsening of the condition, which may suggest the need for interventions to optimize the pump-twin's chance for survival. We performed a retrospective analysis of three cases of monochorionic twin pregnancies diagnosed with a twin reversed arterial perfusion (TRAP) sequence during the first and second trimesters. We compared our data with those offered by a review of the literature.

Control study of the ultrasonography with the placental vascular casts of the acardiac twins sequence

Objective To investigate the relationship between the ultrasonography diagnosis in prenatal and the postnatal placental vascular casts of the twins reversed arterial perfusion(TRAP) sequence. Methods Six cases of TRAP sequence underwent the two-dimensional and color Doppler ultrasonography, and performed placental vascular casts after termination of pregnance. Results According to the anatomical features and ultrasonography, there were 3 cases of acardius acephalus( IV) ,2 cases of acardius anceps( II ) , and 1 case of acardius acormus( I ). In all 6 cases,there were arterio-arterial and veno-venous anastomoses at the level of the chorionic plate between the normal co-twin and the acardiac twin,these anastmosis vessels were superficial and large calibre, and the distances of the placental insertions of the umbilical cords were different,4 cases <0. 5 cm, 2 cases were 4-5 cm. In 4 cases, the vessels entered and went out of the acardiac twin were just one large umbilical artery and one large umbilical vein. In 2 cases, the umbilical artery and umbilical vein had many vascular branches in the placenta. Out of 6 cases of the pump twin, 4 cases died,and 2 cases survived. Conclusions Ultrasonography was consistent with the placental vascular casts,the contrast observing gives us new information for the further research of the special type of the vascular anastmosis and prognosis of the TRAP sequence. Key words: Ultrasonography; Twins reversed arterial perfusion sequence; Placenta; Corrosion casting

Monoamniotic twin pregnancy discordant for lethal open cranial defect: management dilemmas

To report the sonographic findings, prenatal courses, and management options in four cases of monoamniotic twin pregnancy complicated by a discordant, lethal open cranial vault defect. Cases were collected from two Latin American fetal medicine referral centers after the sonographic detection of a monoamniotic twin pregnancy in which one fetus was structurally normal and the other had a lethal open cranial vault defect. Three abnormal fetuses had acrania-anencephaly sequence and one had a large occipital encephalocele. The diagnosis was confirmed at referral, at which time umbilical cord entanglement was also diagnosed with color Doppler ultrasound in all cases. Two cases were managed with selective termination, one of which required referral to a fetal surgery center abroad because this option was illegal in Chile. The other case underwent radiofrequency ablation of the fetal intra-abdominal umbilical vessels after the corresponding ethics and legal committees approved the procedure. In both cases, the non-anomalous twin was born after 35 weeks and had no perinatal complications. Expectant management was performed in the other two cases, resulting in the death of the normal twin at 25 weeks. Monoamniotic twin pregnancy discordant for severe cranial vault defect is a serious condition with a high risk of fetal demise of the structurally normal fetus. Our experience, although limited, suggests that aggressive management with selective termination of the abnormal twin and transection of its umbilical cord in these cases may prevent the demise of the structurally normal co-twin.