<scp>ISUOG</scp> Practice Guidelines (updated): role of ultrasound in twin pregnancy

Abstract

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice, and high-quality teaching and research, related to diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has the remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach, from experts, for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practice at the time at which they are issued. Although ISUOG has made every effort to ensure that Guidelines are accurate when issued, neither the Society nor any of its employees or members accepts any liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. The ISUOG CSC documents are not intended to establish a legal standard of care because interpretation of the evidence that underpins the Guidelines may be influenced by individual circumstances, local protocol and available resources. Approved Guidelines can be distributed freely with the permission of ISUOG ([email protected]). The incidence of multiple pregnancy has increased over the years, mainly due to delayed childbirth and advanced maternal age at conception and the resultant widespread use of assisted reproduction techniques1. In addition to often involving the transfer of more than one embryo, in-vitro fertilization increases the frequency of monozygotic twinning2. The twin birth rate was reported to have increased in the USA by just under 70% between 1980 (19 per 1000 live births) and 2020 (31 per 1000 live births)3, though other reports demonstrated a decline in the twin birth between 2014 and 2018 in both the USA and UK4. Twin pregnancy is associated with a high risk of perinatal mortality and morbidity5-8. There is also an increased risk of maternal complications, such as hypertensive disorders of pregnancy9. In 2019, the stillbirth rate was 7.6 per 1000 twin births compared with 3.8 per 1000 singleton births10. Preterm birth prior to 37 weeks' gestation occurs in up to 60% of multiple pregnancies, while the risk of very preterm birth prior to 32 weeks is 10 times higher in twin compared with singleton pregnancies (10% vs 1%), contributing to the increased risk of neonatal mortality and long-term morbidity11-14. Compared with singleton pregnancies, twin pregnancies are at increased risk of iatrogenic preterm birth due to the greater incidence of maternal and fetal complications. This risk is significantly higher in monochorionic compared with dichorionic pregnancy5-8. Yet, multiple pregnancies are often excluded from research studies, with only 8% of trials on fetal growth restriction (FGR), 17% of those on pre-eclampsia and 2% of those on diabetes including multiple pregnancies15. Moreover, the majority of recommendations in national and international guidelines for the management of multiple pregnancy lack high-quality robust supporting evidence16. Ultrasound assessment of chorionicity, fetal biometry, anatomy, Doppler velocimetry and amniotic fluid volume is used to identify and monitor twin pregnancies at risk of adverse outcomes, such as twin-to-twin transfusion syndrome (TTTS) and FGR. As in singletons, impaired fetal growth can be assessed in twins by comparing biometry and Doppler velocimetry parameters against standards for uncomplicated pregnancy. This guidance will address the role of in the care of uncomplicated twin pregnancies and those by twin twin twins and The guidance on the used to age and chorionicity, for and and for growth and the risk of preterm The management of multiple pregnancy will be in a The and of for trials and and a of from to was The of the was In and the including This was with a transfusion growth and The for and the Guidelines also for guidelines and was the of assessment and clinical practice and clinical The was to the recommendations are and the evidence that while evidence are as practice of the of and of evidence used in Guidelines are in The practice for twin pregnancies is to use the of the twin in the have the use of the or the which both as of pregnancies assisted have that the of the twin best with the The of the is the for the to in the twin is that the twin is that the not the of as age the use of the a in the due by only a and is in any in clinical evidence to the is to with the practice of the of the twin to twin pregnancies in the the weeks' the of the twin be used to the pregnancy. effort be made to the of a twin pregnancy. be weeks of gestation the of the is to the In dichorionic twin the twins are by a of with amniotic one on the of a or compared with only amniotic the in monochorionic twin pregnancy or In for the time weeks of is best the in by the and the fetal is The of the of is as dichorionic are to as a and of monochorionic twin pregnancies have on the of which not the of of monochorionic twins reported to be in a and is more in assisted is that a of than a be more is not to by be is not to chorionicity, a be from a the is the chorionicity, is to the pregnancy as In monochorionic twin pregnancies, or not the twins the amniotic can be from weeks when the amniotic on In of of the is best by is of which is in twin and Doppler with are the or is a used to twin pregnancy in which the has The iatrogenic is used when the in twin pregnancy is as a of or other fetal twin pregnancies be to a with in is that an of the the is and that a is to the As of and is accurate in the when the and have not the is in twin pregnancy is to a for twin to and or and or in the to the of to the and In healthcare Twin is the on the while Twin is the one on the or for can also be used when as they are not to with This be in the in to ensure is to twin as as as to to identify is on the maternal with a and pregnancies with the be by a such as is to that is accurate not in twin in the of be in that the twins as and may not be in that the of is is to and healthcare the birth to in pregnancies in which the twins are for that are not on for or In such an be just prior to and also any neonatal In an uncomplicated dichorionic twin imaging be in the at weeks' gestation and every weeks a is which more In an uncomplicated monochorionic twin an be in the by every weeks from weeks as of has to perinatal the age for of uncomplicated dichorionic twins is considered to be between 37 and 37 and that for uncomplicated monochorionic twins between and as of pregnancy may the risk of perinatal the be fetal biometry, amniotic fluid volume and Doppler from weeks' gestation in monochorionic and from weeks' gestation in dichorionic twin for both in fetal be and at from weeks In monochorionic twin be from weeks in to for In the amniotic fluid volume be assessed and at to for In twin for can be in the the which maternal and and is the of maternal age and the between and weeks of on the clinical healthcare The of a twin occurs in one in of twin pregnancies and is more in those assisted In a comparing maternal and at weeks' gestation in dichorionic pregnancies with a twin or a with those in singleton pregnancies for of conception and age at the of maternal while the a approach, of for be in pregnancies compared to those a that made to the of to for the between and The that in twin pregnancies with a twin on a of maternal and as in singleton the use of and that maternal be only 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