The published literature reports mostly on the outcome of twin pregnancies complicated by twin-twin transfusion syndrome (TTTS) without considering whether the pregnancy is also complicated by another pathology, such as selective fetal growth restriction (sFGR). The aim of this systematic review was to report on the outcome of monochorionic diamniotic (MCDA) twin pregnancies undergoing laser surgery for TTTS that were complicated by sFGR and those not complicated by sFGR.
MEDLINE, EMBASE and Cochrane databases were searched. The inclusion criteria were studies reporting on MCDA twin pregnancies with TTTS undergoing laser therapy that were complicated by sFGR and those not complicated by sFGR. The primary outcome was the overall fetal loss following laser surgery, defined as miscarriage and intrauterine death. The secondary outcomes included fetal loss within 24 h after laser surgery, survival at birth, preterm birth (PTB) prior to 32 weeks of gestation, PTB prior to 28 weeks, composite neonatal morbidity, neurological and respiratory morbidity, and survival free from neurological impairment. All outcomes were explored in the overall population of twin pregnancies complicated by sFGR vs those not complicated by sFGR in the setting of TTTS and in the donor and recipient twins separately. Random-effects meta-analysis was used to combine data and the results are reported as pooled odds ratios (OR) with 95% CI.
Five studies (1710 MCDA twin pregnancies) were included in the qualitative synthesis and four in the meta-analysis. The overall risk of fetal loss after laser surgery was significantly higher in MCDA twin pregnancies with TTTS complicated by sFGR (20.90% vs 14.42%), with a pooled OR of 1.6 (95% CI, 1.3-1.9) (P < 0.001). The risk of fetal loss was significantly higher in MCDA twin pregnancies with TTTS and sFGR for the donor but not for the recipient twin. The rate of live twins was 79.1% (95% CI, 72.6-84.9%) in TTTS pregnancies with sFGR and 85.6% (95% CI, 81.0-89.6%) in those without sFGR (pooled OR, 0.6 (95% CI, 0.5-0.8)) (P < 0.001). There was no significant difference in the risk of PTB prior to 32 weeks of gestation (P = 0.308) or prior to 28 weeks (P = 0.310). Assessment of short- and long-term morbidity was affected by the small number of cases. There was no significant difference in the risk of composite (P = 0.506) or respiratory (P = 0.531) morbidity between twins complicated by TTTS with vs those without sFGR, while the risk of neurological morbidity was significantly higher in those with TTTS and sFGR (pooled OR, 1.8 (95% CI, 1.1-2.9)) (P = 0.034). The risk of neurological morbidity was significantly higher for the donor twin (pooled OR, 2.4 (95% CI, 1.1-5.2)) (P = 0.029) but not for the recipient twin (P = 0.361). Survival free from neurological impairment was observed in 70.8% (95% CI, 45.0-91.0%) of twin pregnancies with TTTS complicated by sFGR and in 75.8% (95% CI, 51.9-93.3%) of those not complicated by sFGR, with no difference between the two groups.
sFGR in MCDA pregnancies with TTTS represents an additional risk factor for fetal loss following laser surgery. The findings of this meta-analysis may be useful for individualized risk assessment of twin pregnancy complicated by TTTS and tailored counseling of the parents prior to laser surgery. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

BACKGROUND: Single fetal demise after intervention for twin-twin transfusion syndrome is a relatively common complication and is often devastating for the patients.
OBJECTIVE: This meta-analysis aimed to evaluate the risk of single fetal demise based on gestational age and Quintero staging at the time of interventions in twin-to-twin transfusion syndrome after fetoscopic laser photocoagulation.
METHODS: Systematic search was performed in PubMed, Web of Science, and Scopus from inception to August 2021. The primary outcome was to compare the incidence of fetal demise between low (I and II) and high (III and IV) twin-to-twin transfusion syndrome Quintero stages. The rate of donor and recipient fetal demise in each stage was compared with that in stage I. Gestational age at fetoscopic laser photocoagulation was compared between surviving fetuses and fetuses that died.
RESULTS: A total of 10 studies (4031 fetuses with twin-to-twin transfusion syndrome) were included in this review. Donor demise was associated with high Quintero stages compared with surviving donors (odds ratio, 2.42; 95% confidence interval, 1.78-3.29; P<.001; I2 , 0%). Recipient fetal demise had a trend for higher Quintero stage compared with surviving recipients, but the analysis did not achieve statistical significance. Pregnancies with donor demise had lower gestational at the time of fetoscopic laser photocoagulation (mean difference, -0.56; 95% confidence interval, -0.93 to -0.18; P=.003; I2 , 36%), whereas pregnancies complicated by recipient demise had similar gestational at time of fetoscopic laser photocoagulation compared with those without demise.
CONCLUSIONS: Demise of the donor fetus was significantly increased after fetoscopic laser photocoagulation for higher stages compared with lower ones. Lower gestational age at the time of fetoscopic laser photocoagulation was associated with an increased risk of single fetal demise in twin-to-twin transfusion syndrome. This was attributed to increased donor demise but not recipient death.

OBJECTIVE: Monochorionic twins with twin-twin transfusion syndrome (TTTS) treated with fetoscopic laser photocoagulation (FLP) are at increased risk of neurodevelopmental impairment (NDI). This meta-analysis aimed to identify the prevalence of and perinatal risk factors for NDI in TTTS survivors treated with FLP.
METHODS: We performed a search in PubMed, EMBASE, Scopus and Web of Science, from inception to 13 February 2021, for studies evaluating perinatal risk factors for NDI in children diagnosed prenatally with TTTS managed by FLP. Data on severity of TTTS at the time of diagnosis, defined according to the Quintero staging system, FLP-related complications and perinatal outcomes were compared between children with a history of TTTS treated with FLP with and those without NDI, which was defined as performance on a cognitive or developmental assessment tool ≥ 2 SD below the mean or a defined motor or sensory disability. A random-effects model was used to pool the mean differences or odds ratios (OR) with the corresponding 95% CIs. Heterogeneity was assessed using the I2 statistic.
RESULTS: Nine studies with a total of 1499 TTTS survivors were included. The overall incidence of NDI was 14.0% (95% CI, 9.0-18.0%). The occurrence of NDI in TTTS survivors was associated with later gestational age (GA) at FLP (mean difference, 0.94 weeks (95% CI, 0.50-1.38 weeks); P < 0.0001, I2  = 0%), earlier GA at delivery (mean difference, -1.44 weeks (95% CI, -2.28 to -0.61 weeks); P = 0.0007, I2  = 49%) and lower birth weight (mean difference, -343.26 g (95% CI, -470.59 to -215.92 g); P < 0.00001, I2  = 27%). Evaluation of different GA cut-offs showed that preterm birth before 32 weeks was associated with higher risk for NDI later in childhood (OR, 2.25 (95% CI, 1.02-4.94); P = 0.04, I2  = 35%). No statistically significant difference was found between cases with and those without NDI with respect to Quintero stage of TTTS, recipient or donor status, development of postlaser twin anemia-polycythemia sequence, recurrence of TTTS and incidence of small- for-gestational age or cotwin fetal demise.
CONCLUSIONS: TTTS survivors with later GA at the time of FLP, earlier GA at delivery and lower birth weight are at higher risk of developing NDI. No significant association was found between Quintero stage of TTTS and risk of NDI. Our findings may be helpful for parental counseling and highlight the need for future studies to understand better the risk factors for NDI in TTTS survivors. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Monozygotic (MZ) twins (\"identical twins\") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to \"overripe ova.\" Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.

Untreated twin-to-twin transfusion syndrome (TTTS) is associated with a high risk of perinatal mortality and morbidity. Laser surgery is recommended before 26 weeks of gestation. However, the optimal management in case of late TTTS (occurring after 26 weeks of gestation) is yet to be established.
We conducted a systematic review and meta-analysis to evaluate the outcomes of monochorionic-diamniotic twin pregnancies complicated by late TTTS according to different management options (expectant, laser therapy, amnioreduction, or delivery). The primary outcome was mortality, including single and double intrauterine, neonatal, and perinatal death. Secondary outcomes were composite morbidity, neuromorbidity, respiratory distress syndrome, admission to neonatal intensive care unit, intact survival (ie, free from neurological complications), and preterm birth before <32 weeks of gestation. Outcomes were reviewed according to the management and reported for the overall population of twins and disease status (ie, donor and recipient separately). Random-effect meta-analyses of proportions were used to analyze the data.
Nine studies including 796 twin pregnancies affected by TTTS were included. No randomized controlled trials were available for inclusion. TTTS occurred at ≥26 weeks of gestation in 8.7% (95% CI 6.9%-10.9%; 67/769) of cases reporting TTTS at all gestations. Intrauterine death occurred in 17.7% (95% CI 4.9%-36.2%) of pregnancies managed expectantly, 5.3% (95% CI 0.9%-12.9%) of pregnancies treated with laser, and 0% (95% CI 0%-9%) after amnioreduction. Neonatal death occurred in 42.5% (95% CI 17.5%-69.7%) of pregnancies managed expectantly, in 2.8% (95% CI 0.3%-7.7%) of cases treated with laser, and in 20.2% (95% CI 6%-40%) after amnioreduction. Only one study (10 cases) reported data on immediate delivery after diagnosis with no perinatal deaths. Perinatal death incidence was 55.7% (95% CI 31.4%-78.6%) in twin pregnancies managed expectantly, 5.6% (95% CI 0.5%-15.3%) in those treated with laser, and 20.2% (95% CI 6%-40%) in those after amnioreduction. Intact survival was reported in 44.4%, 96.4%, and 78% of fetuses managed expectantly, with laser or amnioreduction, respectively.
Evidence regarding perinatal mortality and morbidity in twin pregnancies complicated by late TTTS according to the different managements was of very low quality. Therefore further high-quality research in this field is needed to elucidate the optimal management of these pregnancies.

To report the outcome of pregnancies complicated by twin-twin transfusion syndrome (TTTS) according to Quintero stage.
MEDLINE, EMBASE and CINAHL databases were searched for studies reporting the outcome of pregnancies complicated by TTTS stratified according to Quintero stage (I-V). The primary outcome was fetal survival rate according to Quintero stage. Secondary outcomes were gestational age at birth, preterm birth (PTB) before 34, 32 and 28 weeks\' gestation and neonatal morbidity. Outcomes are reported according to the different management options (expectant management, laser therapy or amnioreduction) for pregnancies with Stage-I TTTS. Only cases treated with laser therapy were considered for those with Stages-II-IV TTTS and only cases managed expectantly were considered for those with Stage-V TTTS. Random-effects head-to-head meta-analysis was used to analyze the extracted data.
Twenty-six studies (2699 twin pregnancies) were included. Overall, 610 (22.6%) pregnancies were diagnosed with Quintero stage-I TTTS, 692 (25.6%) were Stage II, 1146 (42.5%) were Stage III, 247 (9.2%) were Stage IV and four (0.1%) were Stage V. Survival of at least one twin occurred in 86.9% (95% CI, 84.0-89.7%) (456/552) of pregnancies with Stage-I, in 85% (95% CI, 79.1-90.1%) (514/590) of those with Stage-II, in 81.5% (95% CI, 76.6-86.0%) (875/1040) of those with Stage-III, in 82.8% (95% CI, 73.6-90.4%) (172/205) of those with Stage-IV and in 54.6% (95% CI, 24.8-82.6%) (5/9) of those with Stage-V TTTS. The rate of a pregnancy with no survivor was 11.8% (95% CI, 8.4-15.8%) (69/564) in those with Stage-I, 15.0% (95% CI, 9.9-20.9%) (76/590) in those with Stage-II, 18.6% (95% CI, 14.2-23.4%) (165/1040) in those with Stage-III, 17.2% (95% CI, 9.6-26.4%) (33/205) in those with Stage-IV and in 45.4% (95% CI, 17.4-75.2%) (4/9) in those with Stage-V TTTS. Gestational age at birth was similar in pregnancies with Stages-I-III TTTS, and gradually decreased in those with Stages-IV and -V TTTS. Overall, the incidence of PTB and neonatal morbidity increased as the severity of TTTS increased, but data on these two outcomes were limited by the small sample size of the included studies. When stratifying the analysis of pregnancies with Stage-I TTTS according to the type of intervention, the rate of fetal survival of at least one twin was 84.9% (95% CI, 70.4-95.1%) (94/112) in cases managed expectantly, 86.7% (95% CI, 82.6-90.4%) (249/285) in those undergoing laser therapy and 92.2% (95% CI, 84.2-97.6%) (56/60) in those after amnioreduction, while the rate of double survival was 67.9% (95% CI, 57.0-77.9%) (73/108), 69.7% (95% CI, 61.6-77.1%) (203/285) and 80.8% (95% CI, 62.0-94.2%) (49/60), respectively.
Overall survival in monochorionic diamniotic pregnancies affected by TTTS is higher for earlier Quintero stages (I and II), but fetal survival rates are moderately high even in those with Stage-III or -IV TTTS when treated with laser therapy. Gestational age at birth was similar in pregnancies with Stages-I-III TTTS, and gradually decreased in those with Stages-IV and -V TTTS treated with laser and expectant management, respectively. In pregnancies affected by Stage-I TTTS, amnioreduction was associated with slightly higher survival compared with laser therapy and expectant management, although these findings may be confirmed only by future head-to-head randomized trials. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.
Resultado del síndrome de transfusión feto-fetal según el estadio de Quintero de la enfermedad: revisión sistemática y metaanálisis OBJETIVOS: Informar sobre el resultado de los embarazos complicados por el síndrome de transfusión feto-fetal (TTTS, por sus siglas en inglés) según el estadio de Quintero. MÉTODOS: Se hicieron búsquedas en las bases de datos de MEDLINE, EMBASE y CINAHL de estudios que hubieran informado sobre el resultado de embarazos complicados por TTTS, estratificados según el estadio de Quintero (I-V). El resultado primario fue la tasa de supervivencia fetal según el estadio de Quintero. Los resultados secundarios fueron la edad gestacional al nacer, el parto pretérmino (PPT) antes de las 34, 32 y 28 semanas de gestación y la morbilidad neonatal. Los resultados se reportan de acuerdo con las diferentes opciones de tratamiento (expectante, terapia de láser o amniorreducción) para los embarazos con TTTS en Estadio I. Sólo se consideraron los casos tratados con terapia de láser para aquellos con TTTS de las Etapas II-IV y sólo se consideraron los casos tratados de manera expectante para aquellos con TTTS de la Etapa V. Para analizar los datos extraídos se utilizó un metaanálisis directo de efectos aleatorios. RESULTADOS: Se incluyeron veintiséis estudios (2699 embarazos de gemelos). En total, 610 (22,6%) embarazos fueron diagnosticados con TTTS de Estadio I de Quintero, 692 (25,6%) de Estadio II, 1146 (42,5%) de Estadio III, 247 (9,2%) de Estadio IV y cuatro (0,1%) de Estadio V. La supervivencia de al menos un gemelo se produjo en el 86,9% (IC 95%, 84,0-89,7%) (456/552) de los embarazos en Estadio I, en el 85% (IC 95%, 79,1-90,1%) (514/590) de aquellos en Estadio II, en el 81,5% (IC 95%, 76,6-86,0%) (875/1040) de aquellos en Estadio-III, en el 82,8% (IC 95%, 73,6-90,4%) (172/205) de aquellos en Estadio-IV y en el 54,6% (IC 95%, 24,8-82,6%) (5/9) de aquellos en Estadio-V de TTTS. La tasa de embarazos sin supervivientes fue del 11,8% (IC 95%, 8,4-15,8%) (69/564) de aquellos en Estadio-I, 15,0% (IC 95%, 9,9-20,9%) (76/590) de aquellos en Estadio-II, 18,6% (IC 95%, 14,2-23,4%) (165/1040) de aquellos en Estadio-III, 17,2% (IC 95%, 9,6-26,4%) (33/205) de aquellos en Estadio-IV y en el 45,4% (IC 95%, 17,4-75,2%) (4/9) de aquellos en Estadio-V de TTTS. La edad gestacional al nacer fue similar en los embarazos con TTTS en los Estadios I-III, y disminuyó gradualmente en aquellos con TTTS en los Estadios IV y V. En general, la incidencia de PPT y la morbilidad neonatal aumentaron a medida que se incrementó la gravedad del TTTS, pero los datos sobre estos dos resultados se vieron limitados por el pequeño tamaño de la muestra de los estudios incluidos. Al estratificar el análisis de los embarazos con TTTS en Estadio I según el tipo de tratamiento, la tasa de supervivencia fetal de al menos un gemelo fue del 84,9% (IC 95%, 70,4-95,1%) (94/112) en los casos tratados de forma expectante, del 86,7% (IC 95%, 82,6-90.4%) (249/285) en los sometidos a terapia láser y del 92,2% (IC 95%, 84,2-97,6%) (56/60) en los sometidos a amniorreducción, mientras que la tasa de supervivencia doble fue del 67,9% (IC 95%, 57,0-77,9%) (73/108), del 69,7% (IC 95%, 61,6-77,1%) (203/285) y del 80,8% (IC 95%, 62,0-94,2%) (49/60), respectivamente. CONCLUSIONES: La supervivencia en general en los embarazos biamnióticos monocoriónicos afectados por TTTS es mayor en los estadios tempranos de Quintero (I y II), pero las tasas de supervivencia fetal son moderadamente altas incluso en aquellos con TTTS en estadios III o IV cuando se tratan con terapia láser. La edad gestacional al nacer fue similar en los embarazos con TTTS en los Estadios I-III, y disminuyó gradualmente en aquellos con TTTS en los Estadios IV y V tratados con láser y tratamiento expectante, respectivamente. En los embarazos afectados por TTTS en Estadio I, la amniorreducción estuvo asociada con una supervivencia ligeramente mayor en comparación con la terapia de láser y el tratamiento expectante, aunque estos hallazgos solo pueden confirmarse mediante futuros estudios aleatorizados directos. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.
根据Quintero分级的双胎输血综合征预后:系统评价与meta分析 目的: 根据Quintero分级，报告双胎输血综合征(TTTS)患者的预后。 方法: 根据Quintero分级(1-5级)，在MEDLINE(美国医学文献联机数据库)、EMBASE(荷兰医学文摘数据库)和CINAHL(护理学数据库)中进行检索，找出报告双胎输血综合征(TTTS)患者预后的研究。根据Quintero分级，主要预后指标是胎儿的存活率。其次是出生时胎龄、孕期在34周、32周和28周之前的早产(PTB)，以及新生儿发病率。针对1级TTTS患者，根据不同的治疗方案(期待治疗、激光治疗或羊水减量术)来报告预后。对2-4级TTTS患者仅考虑使用激光治疗，而对5级TTTS患者则仅考虑期待治疗。对提取数据进行了随机效应头对头meta分析。 结果: 包含26项研究(2699个双胎妊娠)。总的说来，610个妊娠(占22.6%)被诊断为Quintero分级1级TTTS，692个妊娠(占25.6%)被诊断为Quintero分级2级TTTS，1146个妊娠(占42.5%)被诊断为Quintero分级3级TTTS，247个妊娠(占9.2%)被诊断为Quintero分级4级TTTS，以及四个妊娠(占0.1%)被诊断为Quintero分级5级TTTS。1级患者双胎中至少有一胎存活的占86.9%(95% CI，84.0-89.7%)(456/552)，2级患者双胎中至少有一胎存活的占 85%(95% Ci，79.1-90.1%)(514/590)，3级患者双胎中至少有一胎存活的占81.5% (95% CI，76.6-86.0%)(875/1040)，4级患者双胎中至少有一胎存活的占82.8% (95% CI, 73.6-90.4%)(172/205)，以及5级患者双胎中至少有一胎存活的占54.6% (95% CI, 24.8-82.6%)(5/9)。无胎儿存活的概率在1级患者中占11.8%(95% CI，8.4-15.8%)(69/564)，在2级患者中占15.0%(95% CI，9.9-20.9%)(76/590)，在3级患者中占18.6%(95% CI，14.2-23.4%)(165/1040)，在4级患者中占17.2%(95% CI，9.6-26.4%)(33/205)，以及在5级患者中占45.4%(95% CI，17.4-75.2%)(4/9)。出生时胎龄在1-3级患者中均类似，而在4-5级TTTS患者中逐渐降低。总体来看，PTB发生率和新生儿发病率随着TTTS严重程度的增加而增加，但这两种结果的相关数据受到所包含研究的小样本限制。当根据医疗干预类型来分层分析1级TTTS患者时，在采取期待治疗的病例中，双胎中至少有一胎存活的占84.9%(95% CI，70.4-95.1%)(94/112)；在采取激光治疗的病例中， 双胎中至少有一胎存活的占86.7%(95% CI，82.6-90.4%)(249/285)，而在进行了羊水减量术的病例中，双胎中至少有一胎存活的占92.2%(95% CI，84.2-97.6%)(56/60)。对于这三种医疗干预类型，双胎存活率分别为67.9%(95% CI，57.0-77.9%)(73/108)，69.7%(95% CI，61.6-77.1%)(203/285)和80.8%(95% CI，62.0-94.2%)(49/60)。 结论: 在患有TTTS的单绒毛膜囊双羊膜囊妊娠中，Quintero分级越早期(1级和2级)，总体存活率越高，但在采取了激光治疗的3级或4级患者中均有较高的胎儿存活率。出生时胎龄在1-3级患者中均类似，而在4级和5级(分别采取激光和期待治疗的)TTTS患者中逐渐降低。在1级TTTS患者中，与激光治疗和期待治疗相比，羊水减量术有略高的存活率，然而，这些研究结果也许只有通过将来的头对头随机试验来进行确认。版权 © 2020 ISUOG。由威利父子公司(John Wiley & Sons Ltd)出版。.

Twin-to-twin transfusion syndrome (TTTS) is associated with a high risk of perinatal mortality and morbidity if not treated. However, the optimal timing and management in case of early (occurring < 18 weeks) TTTS has not been established yet.
This is a systematic review and meta-analysis aiming at evaluating the outcomes of monochorionic diamniotic twin pregnancies complicated by early (ie before 18 weeks) TTTS according to different management options (expectant, laser therapy, amnioreduction or cord occlusion). The primary outcome was mortality, including single and double intrauterine, neonatal and perinatal death. Secondary outcomes were: composite morbidity, neuromorbidity, respiratory distress syndrome, admission to neonatal intensive care unit, intact survival (defined as survival free from neurological complications) and preterm birth < 32 weeks of gestation. All outcomes were reviewed according to the different management options (expectant, laser therapy, amnioreduction or cord occlusion) and reported FOR the overall population of twins, and for the donor and recipient separately. Subgroup analysis for TTTS occurring before 16 weeks of gestation was performed. Random-effect meta-analyses of proportions were used to analyse the data.
Thirteen studies were included. Early TTTS occurred in 14.3% (95% confidence interval [CI] 11.9-17.0) of cases. The incidence of intrauterine death was 19.0% (95% CI 2.6-45.5) in twins managed expectantly, 32.4% (95% CI 16.5-50.7) in those who received laser treatment and 12.5% (95% CI 4.8-23.0) in those treated with amnioreduction. The incidence of neonatal death was 22.6% (95% CI 4.2-49.8) in twins managed expectantly, 24.7% (95% CI 0.5-80.3) in those who received laser and 20.2 (95% CI 5.8-43.4) in those who had amnioreduction; it was not possible to compute the incidence of these outcomes in twins undergoing cord occlusion because of insufficient sample and lack of reporting of most of the observed outcomes. Overall, the incidence of perinatal death was 43.9% (95% CI 5.9-87.7) in twins managed expectantly, 47.3% (95% CI 21.4-70.0) in those treated with laser and 28.5% in those who had amnioreduction.
Twin pregnancies affected by early TTTS are at substantial risk of perinatal mortality and morbidity; however, the data come from very small studies with a high risk of selection bias.

BACKGROUND: Single intrauterine fetal death affects approximately 6% of twin pregnancies and can have serious sequelae for the surviving co-twin.
OBJECTIVE: Determine the prognosis of the surviving co-twin following spontaneous single intrauterine fetal death to aid counselling patients and highlight future research areas.
METHODS: Medline, Embase, Web of Science, and Cochrane Library, from 1980 to June 2017.
METHODS: Studies of five or more cases of spontaneous single intrauterine fetal death after 14 weeks gestation, in diamniotic twin pregnancies.
METHODS: Summary event rates were calculated and stratified by chorionicity. Monochorionic and dichorionic twins, and sub-groups, were compared by odds ratios.
RESULTS: In monochorionic twins, when single intrauterine fetal death occurred at less than 28 weeks\' gestation, this significantly increased the rate of co-twin intrauterine fetal death [odds ratio (OR) 2.31, 95% confidence interval (CI) 1.02-5.25, I2  = 0.0%, 12 studies, 184 pregnancies] and neonatal death (OR 2.84, 95% CI 1.18-6.77, I2  = 0.0%, 10 studies, 117 pregnancies) compared with when the single intrauterine fetal death occurred at more than 28 weeks\' gestation. Neonatal death in monochorionic twins was significantly higher if the pregnancy was complicated by fetal growth restriction (OR 4.83, 95% CI 1.14-20.47, I2  = 0.0%, six studies, 60 pregnancies) or preterm birth (OR 4.95, 95% CI 1.71-14.30, I2  = 0.0%, 11 studies, 124 pregnancies). Abnormal antenatal brain imaging was reported in 20.0% (95% CI 12.8-31.1, I2  = 21.9%, six studies, 116 pregnancies) of surviving monochorionic co-twins. The studies included in the meta-analysis demonstrated small study effects and possible selection bias.
CONCLUSIONS: Preterm birth was the commonest adverse outcome affecting 58.5 and 53.7% of monochorionic and dichorionic twin pregnancies. Outcomes regarding brain imaging and neurodevelopmental comorbidity are an important area for future research, but meta-analysis may be limited due to different methods of assessment.
UNASSIGNED: Preterm birth is the highest risk in single co-twin death. Abnormal antenatal brain imaging was found in 1/5 surviving MC twins.

Monochorionic twin pregnancies are high-risk, however at present, no screening test is available to predict which monochorionic twin pregnancy will develop complications.
We sought to assess ability of first-trimester pregnancy-related factors (ultrasound measurements, maternal characteristics, biomarkers) to predict complications in monochorionic twin pregnancies.
Data sources were MEDLINE, Embase, ISI Web of Science, CINAHL, the Cochrane Central Registration of Controlled Trials and Research Registers, and Google Scholar, from inception to May 12, 2017. Gray literature and bibliographies of articles were checked.
Studies that reported ultrasound measurements, maternal characteristics, or potential biomarkers, measured in the first trimester in monochorionic-diamniotic twin pregnancies, where the potential prognostic ability between the variable and twin-twin transfusion syndrome, growth restriction, or intrauterine fetal death could be assessed, were included.
Quality assessment was evaluated using the Strengthening the Reporting of Observational Studies in Epidemiology checklist by 2 reviewers independently. For meta-analysis, odds ratios using a random effects model, or standardized mean difference were calculated. If a moderate association was found, the prognostic ability was evaluated by calculating the sensitivity and specificity. Risk of heterogeneity was reported as I2 and publication bias was visually assessed by funnel plots and quantitatively by Egger test.
In all, 48 studies were eligible for inclusion. Twenty meta-analyses could be performed. A moderate association was demonstrated in 3 meta-analyses, between: nuchal translucency >95th centile in one/both fetuses and twin-twin transfusion syndrome (odds ratio, 2.29 [95% confidence interval, 1.05-4.96], I2 = 6.6%, 4 studies, 615 pregnancies); crown-rump length discordance ≥10% and twin-twin transfusion syndrome (odds ratio, 2.43 [95% confidence interval, 1.13-5.21], I2 = 14.1%, 3 studies, 708 pregnancies); and maternal ethnicity and twin-twin transfusion syndrome (odds ratio, 2.12 [95% confidence interval, 1.17-3.83], I2 = 0.0%, 5 studies, 467 pregnancies), but none demonstrated a prognostic ability for any outcome under investigation.
It is not currently possible to predict adverse outcomes in monochorionic twin pregnancies. We have revealed a lack of research investigating first-trimester biomarkers in monochorionic twin pregnancies. Different assessment methods and definitions of each variable and outcome were an issue and this highlights the need for a large cohort study to evaluate these factors.

OBJECTIVE: Twin-twin transfusion syndrome (TTTS) is associated with significant mortality and morbidity. Potential treatments for the condition require robust evaluation. The aim of this study was to evaluate outcome reporting across observational studies and randomized controlled trials assessing treatments for TTTS.
METHODS: Cochrane Central Register of Controlled Trials, EMBASE and MEDLINE were searched from inception to August 2016. Observational studies and randomized controlled trials reporting outcome following treatment for TTTS in monochorionic-diamniotic twin pregnancy and monochorionic-triamniotic or dichorionic-triamniotic triplet pregnancy were included. Outcome reporting was systematically extracted and categorized.
RESULTS: Six randomized trials and 94 observational studies were included, reporting data from 20 071 maternal participants and 3199 children. Six different treatments were evaluated. Included studies reported 62 different outcomes, including six fetal, seven offspring mortality, 25 neonatal, six early childhood and 18 maternal/operative outcomes. Outcomes were reported inconsistently across trials. For example, when considering offspring mortality, 31 (31%) studies reported live birth, 31 (31%) reported intrauterine death, 49 (49%) reported neonatal mortality and 17 (17%) reported perinatal mortality. Four (4%) studies reported respiratory distress syndrome. Only 19 (19%) studies were designed for long-term follow-up and 11 (11%) of these reported cerebral palsy.
CONCLUSIONS: Studies evaluating treatments for TTTS have often neglected to report clinically important outcomes, especially neonatal morbidity outcomes, and most are not designed for long-term follow-up. The development of a core outcome set could help standardize outcome collection and reporting in TTTS studies. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.