Data from UK confidential enquiries suggest a declining rate of twin stillbirth in monochorionic (MC) and dichorionic (DC) twin pregnancies with improved outcomes possibly reflecting the establishment of national guidelines for the management of multiple pregnancies. Despite this, twin pregnancies are at greater risk of all pregnancy complications, miscarriage and stillbirth than singleton pregnancies. Monochorionic twins, comprising approximately 20% of twin pregnancies, are at particular risk of fetal loss due to the unique pathological complications of a shared placenta: Twin to Twin Transfusion Syndrome (TTTS), early-onset severe selective growth restriction (sGR) and twin anaemia polycythaemia sequence (TAPS). Furthermore, following single intrauterine fetal demise (sIUFD) surviving monochorionic co-twins are exposed to an increased risk of intrauterine death, neonatal death and neurological disability. This chapter examines single and double fetal loss in DC and MC twin pregnancies, outlining the key facts, and covering the difficult issues and management challenges posed by twin demise.

The prevalence of multiple pregnancies is increasing over the last few decades. This is due in part due to use of assisted reproductive techniques which are associated with a higher prevalence of multiple gestation compared to spontaneous conceptions. There is considerable evidence to suggest that combined screening for fetal aneuploidies is equally effective for twin pregnancies as it is in singletons. This along with a relatively higher rate of fetal defects requires accurate prenatal diagnosis. There is evidence from large cohort studies, systematic reviews and meta-analysis that the risk of procedure-related loss in singleton pregnancies is not significantly higher than the background rate of miscarriages. The number of studies examining the procedure-related loss in twin pregnancies following invasive procedures is fewer compared to singleton pregnancies. Although the background rate of pregnancy loss is higher in multiple pregnancies compared to singletons, there is evidence from recent systematic reviews and meta-analysis that the procedure-related loss following invasive procedures is not significantly higher compared to the background rate of loss in twin pregnancies. Invasive prenatal procedures in dichorionic and monochorionic multiple pregnancies have unique challenges including technical skill, rates of complications and sampling errors and therefore such procedures should be carried out by experienced operators in Fetal Medicine centres.

Twin reversed arterial perfusion sequence (TRAP) is a rare complication of monochorionic twins consisting of complete retrograde blood perfusion with consequent developmental disruption and malformation of one twin (acardiac twin), blood bypass of the placenta and subsequent hemodynamic overload in the otherwise normally developed twin (pump twin). Recent studies have identified a higher incidence than historically reported and identification in early pregnancy is crucial to establish opportune diagnosis and management. If not detected, the survival rate of the pump twin is only 50 – 60%, as heart failure, fetal hydrops and intrauterine death may develop, as well as miscarriage or preterm delivery may occur. As a result of increasing awareness and early diagnosis, treatment options have shifted from the second to the first trimester in recent years, although optimal timing and mode of intervention is still controversial. In this chapter the incidence, pathophysiology and clinical presentation of TRAP sequence will be discussed, as well as different therapeutic options will be addressed.

Twin, triplet and higher-order multiple pregnancies experience an increased risk of preterm birth, stillbirth and neonatal death compared to singleton pregnancies. The Twins Trust’s Maternity Engagement programme has found that implementation of National Institute for Health and Care Excellence (NICE) guideline and quality standard lowered these rates. However, a survey of care conducted in 2019 showed that the eight quality standards are followed inconsistently across the UK. Furthermore, parents report a severe lack of support from healthcare services in the postnatal period. Multiple pregnancy charities provide services and resources to professionals working in antenatal and neonatal care to improve their practice and adherence to health care guidance. Charities also provide a wealth of resources to parents in order to guide them through the unique situation of becoming a parent to twins, triplets or more, from pregnancy, throughout the early years, school years and adolescence, into adulthood.

The advances in assisted reproductive techniques combined with the advanced age of women trying to conceive has led to increased implementation of these techniques in order to overcome fertility barriers. An inevitable consequence of assisted reproduction is the raised incidence of multiple pregnancies, mainly twin pregnancies.1

Over the last 30 years there has been a gradual decrease in the vaginal delivery of twins. This may have led to a loss of obstetric intrapartum skills and confidence in some accoucheurs. Leading professional organizations recommend that all women with a cephalic presenting twin be counseled about the availability and safety of vaginal delivery. There are a number of different techniques for delivering twins and the accoucheur should be adept at all, and tailor their practice to the clinical situation in the moment, rather than relying on a single technique. Techniques for vaginal birth in multiple pregnancy have evolved in an anecdotal fashion and there is wide variation in practice throughout the world. None of the techniques are a challenge to a person of average dexterity and an Obstetrics department can safely increase the rate of vaginal delivery of twins through a program of needs assessment, education, simulation, and clinical backup. Some still advocate for the vaginal delivery of triplets, but such practice is rare and as a consequence questionable. The delivery of quadruplets and greater is by caesarean delivery.

Chorioamnionicity is a crucial factor in the risk assessment of a multiple pregnancy. Although knowledge of zygosity is of limited clinical importance, the early identification of the number of fetuses and determination of their chorionicity and amnionicity is critical to proper obstetric management. Prenatal ultrasound permits early and accurate diagnosis of chorioamnionicity. The sonographic features of monochorionicity versus dichochorionicity in the early first trimester, late first trimester, and second and third trimesters share many similarities but significant variation occurs with advancing gestation. While some sonographic findings have very high predictive values and can be confidently used to establish chorioamnionicity, others are less reliable. Therefore, evaluation of as many features as possible should be performed during obstetric ultrasound.

Conjoined twins are a rare anomaly with a high rate of in-utero and perinatal mortality. They are physically joined in ventral, lateral or dorsal unions and may be detected early in prenatal care with ultrasound. The prognosis and ability to separate conjoined twins is specific to their anatomy. Extensive prenatal and postnatal evaluation with a combination of sonography, computed tomography, magnetic resonance imaging, echocardiography and fluoroscopy are used together in order to tailor a care plan for each patient. Conjoined twins are typically delivered as scheduled surgical deliveries,and may be managed postnatally with 1) non-operative management, 2) emergency separation, or 3) planned surgical separation.

The rate of structural malformations in monozygotic twins is higher than in dizygotic twins or singletons. The mechanical process of the embryo splitting may precipitate structural abnormalities leading to this higher incidence. Despite being genetically identical, monozygotic twins can be discordant for structural abnormality. Among the most common structural malformations in twin pregnancies are cardiac anomalies, neural tube and brain malformations, gastrointestinal and abdominal wall defects. Congenital heart disease is more prevalent in monochorionic twins, a proportion of which is caused in response to the abnormal physiology of twin-twin transfusion syndrome. First trimester ultrasound can identify those twin pregnancies at a higher risk of structural malformations and therefore lead to earlier detailed anatomy ultrasound and earlier prenatal diagnosis.

Arguably the most common cause of perinatal mortality and morbidity in multiple gestation is spontaneous preterm labour and delivery. A number of interventions have been evaluated in preventing spontaneous preterm birth in this this context, namely, bed rest (with or without hospitalization), oral tocolytics, home uterine activity monitoring, use of progesterone, cervical cerclage and cervical pessary. Most of the research is in this area relates to twin pregnancy with very little dedicated to triplet and higher order pregnancies. There are conflicting results but in the main, sadly, an effective primary preventative intervention remains elusive. This chapter will summarise what we know about the efficacy of the aforementioned interventions and highlight some specific scenarios where intervention may be beneficial.

Women with multiple pregnancies are at increased risk of pregnancy complications. However, there are very few high-quality studies to direct recommendations for lifestyle modifications in women with twin pregnancies, and such research is virtually non-existent for triplets and above. Several retrospective studies suggest that improved nutrition and proper weight gain might be beneficial to women with twin pregnancies and reduce the risk of fetal growth restriction and preterm birth. Therefore, we recommend nutritional counseling and attempts to achieve recommended weight gain thresholds. In the absence of complications, most women with twin pregnancies can exercise regularly, continue working, and have no restrictions in sexual activity. Most women with twin pregnancies can travel up to 28-32 weeks, provided they have access to medical care, do not have other significant complications, and accept the small possibility of a complication at their destination.

Multiple pregnancy is associated with an increased risk of both maternal and foetal morbidity and mortality. A successful outcome requires a multidisciplinary approach involving obstetricians, neonatologists, obstetric anaesthetists, and midwives. The obstetric anaesthetist may be involved in antenatal assessment, care planning and counselling of parturients with multiple gestation. This is particularly important in pregnant women with medical comorbidities associated with special care needs and increased risk of perinatal complications or adverse outcomes. In twin vaginal delivery, effective epidural in labour is crucial not only for adequate analgesia but it may also increase the chances of successful delivery of the second twin. Providing safe and effective spinal anaesthesia, or general anaesthesia when indicated, for caesarean delivery is essential. A multimodal approach to postoperative analgesia enables enhanced recovery and early discharge after caesarean section. The role of the anaesthetist is crucial in managing critically ill pregnant women including those with pre-eclampsia and its complications. This chapter will cover the anaesthetist’s role in the context of multiple pregnancy.

Twin anemia-polycythemia sequence (TAPS) is a transfusion imbalance unique to monochorionic twin pregnancies, characterized by anemia in the donor and polycythemia in the recipient. TAPS is caused by a chronic transfer of blood through minuscule anastomoses. TAPS can be diagnosed before birth by measuring the middle cerebral artery peak systolic velocities in both twins. If not detected, TAPS may lead to fetal demise. Although we do not know the best management, fetoscopic laser surgery and intrauterine transfusion of the donor with partial exchange transfusion of the recipient, may improve the outcome and prolong the pregnancy. Therefore, current guidelines recommend that we should screen monochorionic twin pregnancies for the occurrence of TAPS. In this chapter, we address our current understanding of TAPS, as well as the issues that need further research. We also propose a management plan based on the severity of the disease and the gestational age at presentation.

Screening for aneuploidies should be offered in twin pregnancies, but it is complicated by several factors. While monozygotic twins are genetically identical and one risk estimation is provided for the whole pregnancy, dizygotic twins require a risk estimation for each fetus. Screening by maternal age alone is currently not recommended because of its poor performance; however, screening by fetal nuchal translucency thickness, the first trimester combined test or cell free DNA testing are effective methods of screening which show similar performance in twin pregnancies as compared to singleton pregnancies. The performance of the second trimester quadruple test is much poorer in twin than in singleton pregnancies and therefore its use should be limited to those cases where other methods are not available. For multiple pregnancies of order three or higher, a combination of maternal age and fetal nuchal translucency thickness provides the best performance.

The incidence of twin and higher order multiple pregnancies increased dramatically with the advent of Assisted Reproductive Technology (ART) in the 1970s, but practice guidelines have led to decreasing numbers from 2014 onwards. All types of twins have increased in incidence, but dizygous much more so than monozygous. Monochorionic placentation is peculiar to monozygotic pregnancies. Higher orders of chorionicity can occur in monozgotic pregnancies, but are much more common in gestations of plural zygosity. There are many factors that affect the incidence of multiple gestation: individual, genetic, and environmental. However, prudent ART management is the simplest and most effective way of reducing the incidence. Multifetal pregnancy reduction is an operative intervention that can reduce the unwanted medical and social sequelae of multiple pregnancy, counseling about such an intervention should be non-directional and carried out by a specialist.

Multiple pregnancy newborns, particularly twins, will generally experience favorable short term outcomes and develop normally. However, these infants will occasionally present significant challenges to the neonatal care provider due to difficulties in extrauterine life adaptation, a spectrum of organ immaturity conditions resulting from preterm delivery, and other biologic risks. Adverse outcomes more likely to present in multiples include intrauterine growth restriction, placental complications, prematurity-related conditions, and congenital anomalies. These infants, even when born extremely premature, are more likely to survive today than years ago due to vast improvements in high risk obstetric and neonatal intensive care. Given the increased likelihood of high-risk conditions and complications, multiple pregnancy newborns should be delivered in hospitals with trained, experienced staff to support the newborns’ immediate needs and better ensure their optimal outcomes. Families of multiples may be at greater risk for stress, anxiety, and depression, and may require specialized and individualized teaching, counseling, and support during the newborns’ admission and after discharge.