The main focus is on the diagnosis and management of complications of twin pregnancies, including twin-to-twin complications, such as inconsistent twin growth, structural abnormalities in one fetus, and intrauterine fetal death in one fetus; and special complications of single-chorionic twin pregnancies, such as twin-to-twin transfusion syndrome (TTTS), selective intrauterine growth restriction (sIUGR), twin reversed arterial perfusion sequence (TRAPS), and twin anemia-polycythemia sequence (TAPS). selective intrauterine rowth restriction (sIUGR), twin reversed arterial perfusion sequence (TRAPS), twin anemia-polycythemia sequence (TAPS), and twin anemia-polycythemia sequence (TAPS). The most common complications of twin pregnancies, especially those of the twin anemia- polycythemia sequence (TAPS), are the lack of a clear-cut picture. Due to the low overall incidence of twin pregnancy complications, especially monochorionic twin complications, there is a lack of randomized controlled studies with large samples, and many relevant clinical findings are based on expert consensus and empirical conclusions, and the management of certain complications is still controversial. The recommendations in this guideline are based on the highest level of published evidence to date and need to be updated and improved as clinical practice evolves.
I. Complications of biventricular twin pregnancy
(i) Inconsistent growth of biventricular twin fetuses
Question 1: How to diagnose biventricular dichorionic fetal growth inconsistency?
The American College of Obstetricians and Gynecologists (ACOG) recommends that a difference of 15%-25% in birth mass between two fetuses is considered to be a fetal growth inconsistency. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends that a difference of >20 mm in abdominal circumference or >20% in estimated fetal mass is considered a growth disparity between the two fetuses. The Royal College of Obstetricians and Gynecologists of the United Kingdom defines inconsistent growth as a difference of >25% in the estimated body mass of the two fetuses.
The majority of fetal medicine centers in China recommend a difference in estimated fetal mass of ≥25% as the diagnostic criterion. Currently, there is no widely accepted growth curve for normal twin estimated body masses, and SOGC and ACOG believe that a growth curve for a normal singleton fetus can be used instead of a twin fetus (evidence level IIa to IIb).
Question 2: What are the reasons for the inconsistent growth of dual chorionic twins?
Expert opinion or recommendation】 Inconsistent growth of biploidy twins may be related to different genetic potential of the two fetuses, structural abnormality of one fetus, chromosomal abnormality or abnormal percentage of placenta occupied by small fetuses. Among placental factors placental weight, proportion of placental area, and abnormal insertion of the umbilical cord (racket or sail attachment) are significantly associated with inconsistent growth in twin fetuses. in 2012, Kent et al [7] used a multicenter retrospective study of 668 cases of biploidy chorionic twins with inconsistent growth showed that a small fetus had an increased proportion of infarcts, retroplacental hemorrhage, and chorionic hematoma than a larger fetus.
Question 3: Can inconsistent growth of biploidy twins be predicted in early pregnancy?
The National Institute for Health and Care Excellence (NICE) guidelines for the management of twin fetuses published in 2011 state that a difference in fetal head-rump length of ≥10% in early pregnancy is a high risk factor for perinatal mortality, with a small fetus at risk of increased risk of structural or chromosomal abnormalities (level of evidence IIb).
In 2014, a meta-analysis by D’Antonio et al [9] showed that inconsistency in fetal head-rump length in early pregnancy in dichorionic twins predicted the risk of occurrence of twin growth inconsistency (RR=2.24, p<0.01); in 2013, a multicenter consecutive prospective study of 960 twin pregnancies by O'Connor et al showed that fetal abdominal circumference measured at 14 to 22 weeks of gestation differences in fetal abdominal circumference measured at 14-22 weeks of gestation had a better predictive value for inconsistent twin fetal growth.
Question 4: What is the management of dichorionic twin growth dysplasia in mid to late gestation?
Expert opinion or recommendation] It is recommended to refer pregnant women with dichorionic growth disorders to an experienced prenatal diagnostic center for detailed fetal structure screening and consultation and decision on the need for fetal genetic testing (recommendation level B).
In 2013, Harper et al. conducted a single-center retrospective study in which 895 pregnant women with biploidy twins were enrolled, 63 of whom were in the inconsistent growth group and the rest in the control group. The results showed that there was no statistically significant difference in the incidence of preterm delivery (34.9% and 25.6%, respectively) and NICU admission (26.9% and 23.5%, respectively) between the two groups up to 34 weeks of gestation. If biploidy twin fetuses are found to grow inconsistently, monitoring should be intensified in late pregnancy, and the appropriate timing of delivery should be selected by considering the estimated fetal body mass, gestational week and maternal condition (Evidence level IIb).
(ii) Intrauterine fetal death in one of the twin chorionic fetuses
Question 5: The impact of intrauterine fetal death in one of the twin chorionic fetuses on the mother and fetus and the clinical management
Expert opinion or recommendation】 The death of one fetus in a dichorionic twin does not usually affect the other fetus because there is no anastomotic vessel between the placentas. The risk of simultaneous death of the surviving fetus is 4%, the risk of neurological sequelae is 1%, and the most significant risk is preterm delivery. If the surviving fetus does not have high-risk factors or is far from full term gestational age, expectant observation is usually chosen with good outcome.
(iii) Anomalies in one of the twin chorionic twins
Question 6: How to deal with one of the twin chorionic fetuses with anomalies?
Expert’s opinion or recommendation】 In the case of biventricular anomalies (including structural anomalies and chromosomal anomalies), the severity of the fetal anomaly, the impact on the mother and the healthy fetus, and the risk of fetal reduction surgery should be taken into consideration, and the patient’s wishes, ethical and social factors should be taken into account to develop an individualized treatment plan. For severe fetal anomalies, fetal reduction is feasible. Shalev et al. and Hern suggested that for severe non-lethal fetal anomalies (e.g., trisomy 21) in one of the twin chorionic twins detected in mid-trimester, to improve the live birth rate of healthy fetuses, reduction can be observed until late pregnancy, but after 28 weeks of gestation when the perinatal period is reached, there are medical and ethical issues whether reduction can be performed. However, after 28 weeks of gestation and entering the perinatal period, there are medical ethical issues that need to be discussed and decided by the relevant ethics committee.
Special complications during pregnancy of monochorionic twins
(i) TTTS
Question 7: How to diagnose TTTS?
[Expert opinion or recommendation] For pregnant women with monochorionic twins, if there is a significant increase in abdominal circumference or abdominal distension in a short period of time, TTTS should be alerted to occur. If abnormal amniotic fluid volume is detected by ultrasound, referral to a regional qualified prenatal diagnosis center or fetal medicine center is recommended for definite diagnosis (recommendation level E).
TTTS is a complication specific to monochorionic twin pregnancies and accounts for 10%-15% of complications in monochorionic twins. the pathogenesis of TTTS is unclear, but it is mainly associated with monochorionic twins sharing a common placenta with a large number of vascular anastomoses at the placental level. Untreated TTTS before 24 weeks of gestation has a fetal morbidity and mortality rate of 90% to 100%, with neurological sequelae occurring in up to 17% to 33% of surviving fetuses.
The diagnosis of TTTS is based on the presence of excessive amniotic fluid (maximum depth of amniotic fluid >8 cm before 20 weeks of gestation and >10 cm after 20 weeks of gestation) in one fetus and low amniotic fluid (maximum depth of amniotic fluid <2 cm) in the other fetus during the ultrasound examination of a single chorionic twin. The previous diagnostic criteria of "20% difference in body mass and 5 g/L difference in hemoglobin between the two fetuses" have been abandoned, and the requirement for TTTS diagnosis is the presence of the twin oligopolyhydramnios sequence (TOPS) in both fetuses. The diagnosis of TTTS requires the presence of a twin oligopolyhydramnios sequence (TOPS) in both fetuses and not a difference in body mass between the two fetuses (level of evidence III).
Question 8: How is TTTS staged?
The most commonly used staging for TTTS is the Quintero staging, which was first proposed by Dr. Quintero in the United States in 1999.
Question 9: How to assess the clinical application value of TTTS staging?
[Expert opinion or recommendation] The main basis of Quintero staging is the severity of the disease, which has no significant correlation with the prognosis of the disease, and the progression of TTTS can progress in a jumping pattern. Dickinson and Evans reported the prognosis of 71 pregnant women with TTTS in Quintero staging, and the results showed that 28% of the pregnant women had improvement, 35% of the pregnant women experienced deterioration, and 37% of the pregnant women maintained at the original staging level. The staging did not assess the cardiac function of children with TTTS, which is closely related to the prognosis.
The Children’s Hospital of Philadelphia (CHOP) has proposed a scoring system based primarily on the cardiac function of the recipient fetus, the CHOP score, which assesses the presence of ventricular hypertrophy, cardiac dilatation, right ventricular outflow tract stenosis, tricuspid regurgitation on ultrasound, and venous duct regurgitation. The CHOP score includes the presence of tricuspid regurgitation, venous duct regurgitation, etc. The value of this score for the assessment of fetoscopic procedures and prognosis needs to be validated in a large sample of studies (Level of Evidence IIb).
Question 10: How is TTTS treated?
Expert opinion or recommendation] For TTTS at 16-26 weeks of gestation in Quintero stage II and above, fetoscopic laser treatment should be preferred. TTTS should be treated at a fetal medicine center capable of intrauterine intervention (recommendation level A).
For the treatment of TTTS, the earliest approach was amniotic fluid reduction, aimed at prolonging the gestational weeks by reducing the amniotic cavity pressure, with a postoperative survival rate of 50% to 60% for at least one fetus [23]. Compared to amniotic fluid reduction, fetoscopic laser coagulation of interplacental anastomotic vessels significantly improves the prognosis of children with TTTS.In a randomized controlled study of 142 cases of TTTS, Senat et al. found that the prognosis of children with TTTS treated with fetoscopic laser was significantly better than that of repeated amniotic fluid reduction, with a first-trimester survival rate of about 76% after fetoscopic laser treatment, significantly higher than that of amniotic fluid reduction The mean gestational week of delivery after fetoscopy (33 weeks of gestation) is also later than after amniotic fluid reduction (29 weeks of gestation) (Evidence level Ib).
Currently, the indication for fetoscopic laser for TTTS is Quintero stage II-IV. The prognosis of children with TTTS stage I depends to some extent on the progression of the disease, with 10.0% to 45.5% of children experiencing progression, and this uncertainty of progression is the reason for the controversy over whether children with TTTS stage I should be treated with fetoscopic laser (Level of Evidence Ib). This uncertainty of outcome is the reason for the controversy over the need for fetoscopic laser treatment in children with TTTS stage I (level of evidence IIa).
The optimal gestational age for fetoscopic laser treatment of TTTS is 16 to 26 weeks of gestation. A few medical centers have also performed fetoscopic laser treatment before 16 weeks of gestation and after 26 weeks of gestation. Among the 325 cases of TTTS treated with fetoscopic laser, 283 cases were operated at 17-26 weeks of gestation, with 86.9% survival rate of one fetus and 56.6% survival rate of two fetuses; another 24 cases were operated earlier than 17 weeks and 18 cases were operated >26 weeks of gestation, with the success rate similar to that of 17-26 weeks of gestation. 2004 to present, fetoscopic laser treatment for TTTS has been performed worldwide. treatment of TTTS has been performed in more than 10,000 cases worldwide, and the results of the treatment of TTTS have been widely recognized. In recent years, several fetal medicine centers in China have carried out fetoscopic laser treatment, and the results suggest that the postoperative survival rate of TTTS patients treated with fetoscopic laser is 60.0%-87.9% for at least one fetus and 51.5% for two fetuses, and the average gestational week of delivery is 33-34 weeks of gestation [28-29
(ii) sIUGR
Question 11: What is sIUGR?
The incidence of sIUGR is 10%-15% in monochorionic twins, which is mainly manifested by the difference in body mass between the two fetuses. Hack et al. studied the placenta of 150 monochorionic twins and found that the occurrence, natural course and regression of sIUGR are mainly related to the following two factors: supply uneven ratio of placental area to both fetuses and the presence of different types of placental anastomotic vessels. The latter is a key factor influencing the clinical regression of the disease, and these anastomotic vessels have a compensatory and protective effect, while having a damaging effect when the condition of the small fetus deteriorates. The natural course and outcome of monochorionic twin sIUGR are diverse, and its clinical management is far more challenging than TTTS, and clinical consultation is often more difficult (Level of Evidence III).
Question 12: How is sIUGR diagnosed?
Expert opinion or recommendation] The difference in body mass between two fetuses in monochorionic twins should be suspected as sIUGR. Due to the diversity and complexity of the outcome of sIUGR, referral to an experienced prenatal diagnostic center or fetal medicine center for professional evaluation and consultation is recommended (level of recommendation E).
There is no consensus on the diagnosis of sIUGR. The most widely used definition is the one proposed by Gratacos et al: in monochorionic twins, sIUGR is considered when either fetus has an ultrasound-estimated body mass less than the 10th percentile of the corresponding gestational week. in monochorionic twins, if either fetus has a body mass less than the 10th percentile, more than 95% of the fetuses will also have a discrepancy in body mass between the two fetuses (>25% difference) ( Level of evidence III).
Clinically, sIUGR is often confused with TTTS, especially in cases with uneven distribution of amniotic fluid (one fetus with excess amniotic fluid). The main point of differentiation is that TTTS must meet the diagnostic criteria of both excess amniotic fluid in one fetus and low amniotic fluid in the other fetus.
Question 13: How to perform staging and prognostic counseling for sIUGR?
[Expert opinion or recommendation] Researchers from the Catholic University of Louvain (Belgium) performed ultrasound Doppler flow assessment in 134 cases of sIUGR from 18 to 26 weeks of gestation and proposed a staging method for sIUGR [33]. sIUGR staging is based on ultrasound assessment of the diastolic flow spectrum of the umbilical artery in small fetuses. Type I: normal end-diastolic flow spectrum of the umbilical artery in small fetuses; Type II: persistent absence or inversion of end-diastolic flow in small fetuses; Type III: intermittent absence or inversion of end-diastolic flow in small fetuses.
The prognosis of sIUGR is related to the type. Type I sIUGR has the best clinical prognosis, and it is less common for small fetuses to have growth restriction but deterioration (e.g., absence or inversion of umbilical blood flow). 32 to 34 weeks of gestation, but due to the larger diameter artery-to-artery anastomosis, the occurrence of intrauterine transfusion from the large fetus to the small fetus is often more massive and abrupt, and therefore unpredictable. gratacos et al [33] reported perinatal outcomes in 134 cases of sIUGR, of which 39 cases of type I sIUGR were delivered at a mean gestational week of 35.5 weeks with no neonatal neurological sequelae. The mean gestational week of delivery was 30 weeks in 30 cases of type II sIUGR, and the incidence of cerebral white matter injury was 14.3% in small fetuses and 3.3% in large fetuses; the mean gestational week of delivery was 31.6 weeks in 65 cases of type III sIUGR, and the incidence of cerebral parenchymal injury was 19.7% in large fetuses and 2.0% in small fetuses; the intrauterine mortality rate was 15.4% in small fetuses and 6.2% in large fetuses (Level of evidence IIb).
A systematic analysis of 11 papers related to sIUGR studies by scholars from Leiden University (The Netherlands) in 2014 found that the incidence of brain injury in children with sIUGR was 8%, and the injury was associated with abnormal ultrasound Doppler flow (OR=7.69), intrauterine death in one fetus (OR=2.92) and delivery at <32 weeks gestation (OR=1.56). 1.56), and the probability of brain injury was slightly higher in fetuses with large birth masses than in those with small birth masses (OR=1.93) (Level of evidence III).
Question 14: How to manage sIUGR clinically accordingly?
The clinical management of sIUGR is complex and should be evaluated in detail at an experienced prenatal diagnostic center or fetal medicine center as much as possible to develop a treatment plan (level of recommendation B).
Type I sIUGR mostly has a good pregnancy outcome, and treatment can be expected under close supervision, and those with no deterioration of umbilical blood flow can expect pregnancy up to 35 weeks.
For type II sIUGR, pregnant women and their families should be fully informed of their fetal prognosis, and individualized treatment plans should be formulated based on the severity of the disease, the wishes of the family and the availability of intrauterine intervention in the hospital based on adequate consultation. Treatment options include expectant treatment and intrauterine treatment. For sIUGR, the indication for intrauterine treatment is more difficult to establish. Three factors should be considered when making a decision: (1) the risk of intrauterine fetal death or brain injury; (2) the family’s wishes; and (3) the level of medical technology. Currently, the commonly used intrauterine treatment option is selective fetal reduction.
The aim of selective reduction is to actively subtract the small dying fetus, thus protecting the large fetus. Currently, bipolar electrocoagulation of the umbilical cord or radiofrequency ablation of the umbilical vessels via the fetal abdomen and umbilical cord ligation are used clinically. The choice of procedure is closely related to the size of the gestational week and requires an individualized plan. Fetoscopic laser surgery for sIUGR is currently performed in only a few medical centers worldwide due to the difficulty of the procedure, and the efficacy is uncertain. If anticipatory treatment is chosen, according to previous literature, most small fetuses with type II sIUGR will deteriorate by 32 weeks of gestation, and regular ultrasound examinations are recommended during the anticipatory pregnancy. According to the currently available evidence-based medical evidence, the gestational week for termination of pregnancy is usually not more than 32 weeks. In exceptional cases, close monitoring and appropriate extension of the gestational week are possible, but the risks during the expectant process need to be fully informed. The health of most type III sIUGR fetuses remains stable until 32-34 weeks of gestation, but there is a risk of sudden fetal death and a risk of brain damage in surviving fetuses. The frequency of follow-up is consistent with type II sIUGR when the family requires expectant treatment. Delivery no later than 34 weeks of gestation is recommended.
(iii) Death of one fetus in monochorionic twin fetuses
Expert opinion or recommendation] When intrauterine death of one fetus in monochorionic twins is detected, referral to a regional prenatal diagnostic center or fetal medicine center for detailed evaluation is recommended (recommendation level B).
Question 15: Etiology of intrauterine death of a monochorionic twin fetus
The most common causes of intrauterine death in monochorionic twin fetuses are fetal chromosomal abnormalities, structural developmental abnormalities, TTTS, TAPS, severe sIUGR, and single amniotic sac twin fetuses with umbilical cord entanglement (level of evidence IIb).
Question 16: How to consult the prognosis of the surviving fetus after intrauterine death of a single chorionic twin fetus?
Expert opinion or recommendation] Because of the unique nature of monochorionic twin fetuses, it is recommended that the prognosis of the surviving fetus should be consulted by an experienced specialist (recommendation level A).
After the death of one fetus in monochorionic twin fetuses, the blood of the surviving fetus is backed up to the stillborn fetus due to the vascular anastomosis between the placenta, thus causing acute or prolonged hypotension and hypoperfusion levels, which may lead to the death of the other fetus, and may also cause ischemic injury to the organs of the surviving fetus, especially to the nervous system.
In 2011, a meta-analysis of perinatal outcomes after the death of one fetus in 22 studies of twins found that the risk of simultaneous death of the other fetus after the death of one fetus in monochorionic twins was significantly higher than that in bichorionic twins (15% and 3%, respectively); however, there was no significant difference in the incidence of preterm birth compared with bichorionic twins (68% and 54%, respectively); in postnatal There was a difference in the detection rate of neurological imaging abnormalities (34%, 16%, respectively); and a significant difference in neurological developmental abnormalities in surviving fetuses (26%, 2%, respectively) (Level of evidence Ia).
Question 17: How to manage the pregnancy after the occurrence of one fetal death in monochorionic twins?
Expert opinion or recommendation] It is recommended that the prenatal diagnostic center or fetal medicine center should develop an individualized treatment plan for pregnant women with first trimester death in monochorionic twins (recommendation level B).
The need for immediate delivery of the other surviving fetus after intrauterine death of one of the monochorionic twins is controversial, and there is no strong evidence to guide the conclusion so far. It has been argued that immediate delivery does not improve the prognosis of the surviving fetus on the grounds that neurological damage occurs as a result of a momentary intrauterine “acute transfusion” of the other fetus at the time of death of one fetus, and that immediate delivery does not improve the neurological damage that has already occurred in the surviving fetus, but may increase the incidence of preterm delivery unless Severe abnormalities in fetal heart monitoring or severe anemia in the surviving fetus in late pregnancy are detected. In the surviving fetus, the presence of severe anemia can be determined by ultrasound detection of peak maximum systolic flow velocity in the middle cerebral artery of the fetus. If severe anemia is present, intrauterine transfusion of anemic fetuses can be used to correct the anemia, prolong the gestational cycle, and reduce the risk of neurological injury in surviving fetuses, but is controversial. A cranial MRI scan of the surviving fetus 3 to 4 weeks after the occurrence of intrauterine fetal death may detect some severe fetal cranial injuries earlier than ultrasonography. If imaging reveals neurological lesions in the surviving fetus, a detailed discussion with the family about the prognosis of the fetus is required.
Management of pregnancy in pregnant women focuses on monitoring pregnancy-related complications and comorbidities. Some evidence-based medical evidence suggests an increased incidence of maternal hypertension-related disorders in pregnancy following intrauterine death of one fetus in twin pregnancies, requiring blood pressure monitoring and urine protein screening, and a theoretical but rare clinical report of the risk of disseminated intravascular coagulation. The risk of maternal infection is not increased after the death of one of the monochorionic twins.
(iv) Malformation of one fetus in monochorionic twins
Question 18: How to diagnose, counsel and manage monochorionic twin fetal malformations?
The incidence of fetal malformation in monochorionic twins is 2-3 times higher than that in singleton pregnancies. Individualized counseling should be performed in pregnant women with monochorionic twin fetuses who develop first trimester anomalies, and appropriate monitoring and surgical treatment should be given (recommendation grade B).
Monochorionic twins are 2 to 3 times more likely to have fetal structural abnormalities than singleton pregnancies, such as fetal limb shortage, intestinal atresia, and cardiac malformations, which may be related to abnormal vascular connections between monochorionic twins. Mechanisms such as asymmetric oval sphere division, somatic cell chimerism, and epigenetic modifications can explain the occurrence of many monochorionic twins in which one of the fetuses develops chromosomal abnormalities, neural tube defects, hydrocephalus, and abdominal wall clefts. Once diagnosed, such complicated twins need to be referred for adequate evaluation in an experienced fetal medicine center.
The management of one of the monochorionic twins should be individualized, taking into account the severity of the fetal anomaly, the presence of combined chromosomal abnormalities, the impact on the pregnant woman and the healthy fetus, the risks of reduction surgery, the patient’s wishes, and ethical and social factors. If the decision is made to reduce the fetus, the approach is the same as that for reduction of sIUGR (evidence level III).
(V) TRAPS
Question 19: What is TRAPS?
TRAPS, also known as acardiac twins sequence, is a unique complication of monochorionic twin pregnancies with a 1% incidence. The normal fetus is known as a pumping fetus, and the circulation of the heartless fetus needs to be dependent on the normal fetus. Ultrasonography does not show the heart of the abnormal fetus, but blood flow is visible in the fetus, and the umbilical cord of the abnormal fetus is a single umbilical artery, i.e., into the fetal arterial blood flow, and the heart rate and rhythm shown by its blood flow spectrum are identical to those of the normal fetus. The etiology of this disease is unknown, and the widely accepted hypothesis is the “reverse vascular perfusion theory”.
Question 20: How to manage TRAPS?
Expert opinion or recommendation] Pregnant women with TRAPS should be referred to an experienced prenatal diagnosis center or fetal medicine center for monitoring, appropriate counseling and reasonable treatment plan (recommendation level C).
Some TRAPS, if left untreated, can result in heart failure, edema, and preterm delivery in pumped-blooded infants, with a perinatal morbidity and mortality rate of 50% to 75%. Pumps also have a high incidence of structural abnormalities, with a probability of chromosomal abnormalities of approximately 9%, and should be carefully screened for structural and chromosomal abnormalities.
The treatment of TRAPS is similar to that of monochorionic twins in which one fetus is abnormal, mostly by reduction with vascular coagulation techniques (radiofrequency ablation or umbilical cord coagulation). The need for reduction of a heartless fetus depends on the relative size of the heartless fetus to the pumping fetus and the presence of signs of impaired cardiac function in the pumping fetus. The indications for intrauterine intervention in a heartless fetus include: (1) a heartless fetus with an abdominal circumference equal to or greater than that of the donor; (2) excessive amniotic fluid (maximum depth of amniotic fluid >8 cm); (3) severe ultrasound flow abnormalities in the pumping fetus, including absence or inversion of diastolic flow in the umbilical artery, pulsatile umbilical venous flow or reversed venous catheter flow; (4) edema in the pumping fetus (cavernous fluid accumulation); (5) single amniotic sac prone to umbilical cord entanglement (Level of Evidence II).
(vi) Single chorionic monoamniotic sac twin pregnancies
Q21: How to diagnose and manage a single chorionic monoamniotic sac twin pregnancy?
(Expert opinion or recommendation) Monochorionic monoamniotic pregnancy (MCMA) requires intensive monitoring during pregnancy because of the high risk of cord entanglement.
MCMA accounts for 1%-2% of monochorionic twins, and most of them are formed when the fertilized egg splits after the amniotic sac has formed at 8-13 d of fertilization, so the two fetuses share not only a placenta but also an amniotic sac. MCMA has a high perinatal morbidity and mortality rate, and it has been reported in the literature that about 71% of monochorionic twins have umbilical cord entanglement, and more than 50% of fetal deaths are related to umbilical cord factors. In a retrospective study of 30 pregnant women with MCMA, the overall fetal survival rate was found to be 60%; 8 of 10 twin fetuses with intrauterine mortality were due to cord entanglement, 2 of which occurred after 32 weeks of gestation (level of evidence III).
Although single or double amnioticity can be determined by transvaginal ultrasound at as early as 7 weeks of gestation by the number of yolk sacs, the best time for diagnosis of MCMA is currently considered to be 11 to l4 weeks of gestation. Once MCMA is diagnosed, it should be monitored closely, but there is no consensus on the means of monitoring and the frequency of monitoring. A cesarean section at 32-34 weeks of gestation is recommended for termination of pregnancy. Even so, 12% of perinatal deaths are unavoidable.
(vii) TAPS
Question 22: How is TAPS diagnosed and treated?
TAPS is defined as a chronic fetal-fetal transfusion in monochorionic twin fetuses with severe hemoglobin difference between the two fetuses but without TOPS. The percentage of TAPS is 2-13% after fetoscopic laser surgery. The latest prenatal criteria for the diagnosis of TAPS are <1.0 median times the maximum systolic flow velocity in the middle cerebral artery of the recipient and >1.5 median times the maximum systolic flow velocity in the middle cerebral artery of the donor. Postnatal diagnostic criteria were a difference in hemoglobin between the two fetuses >80 g/L and either of the following conditions: reticulocyte ratio >1.7 in the donor and recipient or placental perfusion revealing only vascular anastomotic branches <1 mm in diameter.
The prognosis of TAPS is poorly reported in the literature. Management of TAPS includes expectant treatment, termination of pregnancy, intrauterine fetal transfusion, selective fetal reduction, or fetoscopic laser surgery. There is no evidence to support which approach is more effective.
(viii) Conjoined twin pregnancies
Question 23: Diagnosis and clinical management of conjoined twin pregnancies
The incidence is about 1/100,000~1/90,000 and is related to abnormal embryonic development. 80%~90% of pregnancies can be terminated by diagnosis at 12~14 weeks of gestation and some cases of intrauterine fetal death. If the diagnosis is not made or if the conjoined twins are found after 24 weeks of gestation, obstructed labor and uterine rupture may occur during induction of labor, and a cesarean section may be required for late pregnancy delivery.