When should twins be delivered?

TY - JOUR

T1 - When should twins be delivered?

AU - Giles-Clark, H. J.

AU - McGannon, C.

AU - Mol, B. W.

N1 - Funding Information: B.W.M. is supported by a NHMRC Investigator grant (GNT1176437). B.W.M. reports consultancy for ObsEva and Merck and travel support from Merck. Funding Information: B.W.M. is supported by a NHMRC Investigator grant (GNT1176437). B.W.M. reports consultancy for ObsEva and Merck and travel support from Merck. The aim of obstetric intervention is to improve the outcome for mothers and their offspring. Whilst parents and care-providers usually focus predominantly on short-term outcome, long-term outcome is, arguably, more important. We believe that, provided a baby survives, prevention of sequelae in the long term should take precedence over that of short-term morbidity. Parents and care-providers would probably be prepared to accept short-term health problems as long as the outcome is good in the long term. The obstetric literature does not reinforce this sentiment. For a variety of reasons, the vast majority of studies investigating obstetric intervention focus on outcomes in the short term, and, at most, until 6 weeks after birth1. Long-term follow-up is expensive, surpassing the normal duration of funding, and the project structure according to which research is normally organized requires interdisciplinary collaboration and faces challenges in terms of privacy and ethics approval. The situation is no different for women with a twin pregnancy. Twin pregnancies are overrepresented in preterm births; up to 60% of twin gestations deliver by 37 weeks2,3. Preterm birth is associated with an increased risk of adverse short-term perinatal outcome, with this risk decreasing as gestational age at delivery increases4. A small number of population-based studies have been published in recent years suggesting that long-term neurodevelopmental delay and a requirement for special education occur more often in late-preterm twins than in those born at term5,6; however, there is an overall paucity of evidence regarding the long-term sequelae of late-preterm twins. The research by Cho and colleagues7, in this issue of the Journal, is, therefore, a welcome addition to the growing body of evidence. This observational study, conducted in Korea using national databases, demonstrates that late prematurity may result in complications that persist into childhood; twins delivered between 34 and 37 weeks had higher risks of short-term and long-term morbidities than did twins delivered after 37 weeks of gestation7. These authors suggest that, in the absence of urgent reasons, twins should not be delivered before 37 weeks. However, they highlight a number of limitations of their study, including the absence of data relating to chorionicity and to the indications for late-preterm delivery and Cesarean section, each of which may contribute significantly to long-term morbidity. Differences in outcome based on chorionicity have been demonstrated consistently; monochorionic twin pregnancies are more likely to deliver prematurely and have greater short-term morbidity than do dichorionic twin pregnancies8–10. The secondary analysis by Cho et al.7 of sex-discordant twins (a proxy to including only dichorionic gestations) showed that sex-discordant late-preterm twins had a higher risk of adverse short-term, but not long-term, outcome compared with the equivalent term twins. This suggests that, rather than gestational age alone, monochorionicity is also a significant contributor to long-term morbidity. In pregnancies in which a clear maternal or fetal indication for expedited delivery exists, preterm delivery is appropriate, and indeed essential, and a poorer outcome is likely to be a result of the indication itself. Furthermore, there is a correlation between earlier gestational age at spontaneous onset of labor and the risk of intrauterine infection and associated perinatal morbidity11,12. Thus, the increased morbidity seen in late-preterm compared with term infants may be impossible to avoid by simply planning to delay elective delivery. The evidence to support the gestational age at which delivery is indicated to avoid late-gestation stillbirth in an otherwise uncomplicated twin pregnancy is inconsistent. Some studies suggest that the rate of intrauterine fetal death in twins increases prior to the estimated due date, whereas other studies have failed to substantiate this13. The consensus is that the nadir of perinatal risks, whereby the risk of neonatal death is balanced by the risk of stillbirth, occurs between 36 and 37 weeks' gestation for monochorionic twins and between 37 and 38 weeks' gestation for dichorionic twins13. The rate of iatrogenic preterm twin delivery has increased over recent years, including for non-complicated twin pregnancies3. There are substantial data to demonstrate that delaying delivery in singletons is associated with better long-term outcome, providing there is no urgent indication for delivery14,15. It has been suggested that, in twins, fetal maturity occurs earlier and, thus, that sequelae would be less pronounced16. This has been countered by multiple studies looking at late-preterm twin outcome which found no evidence of early maturity and better outcome in spontaneous rather than iatrogenic birth10,17,18, supporting the opinion that planned preterm twin birth in the absence of other indications is difficult to justify. No randomized controlled trial has studied long-term outcome associated with different gestational ages at delivery in twins, meaning that any published follow-up of preterm infants must be based on non-randomized data and, therefore, is inadvertently biased. It is probable that the higher rates of developmental and neurodevelopmental morbidity seen in late-preterm twins are not due purely to the gestational age at delivery, rather also being affected by the underlying reasons behind the early delivery, the chorionicity of the pregnancy or other factors. Until more research on the long-term outcome of twins becomes available, like Cho et al.7, we recommend a strategy for delaying delivery of twins until at least 37 weeks, as long as no contraindications to continuing the pregnancy exist and appropriate fetal surveillance is implemented. B.W.M. is supported by a NHMRC Investigator grant (GNT1176437). B.W.M. reports consultancy for ObsEva and Merck and travel support from Merck.

PY - 2022/6

Y1 - 2022/6

UR - http://www.scopus.com/inward/record.url?scp=85131055602&partnerID=8YFLogxK

U2 - 10.1002/uog.24894

DO - 10.1002/uog.24894

M3 - Editorial

C2 - 35229929

AN - SCOPUS:85131055602

VL - 59

SP - 713

EP - 714

JO - Ultrasound in Obstetrics and Gynecology

JF - Ultrasound in Obstetrics and Gynecology

SN - 0960-7692

IS - 6

ER -