Association of Gestational Age at Birth With Risk of Perinatal Mortality and Special Educational Need Among Twins

IMPORTANCE
Twin pregnancies account for 3% of livebirths but experience substantially more perinatal morbidity and mortality than singletons. Optimising the timing of birth is a key strategy in improving twin pregnancy outcome. Current UK and USA policies are based on observational studies of perinatal mortality and not on longer term effects. The impact of timing of birth on long-term childhood outcome in twins is uncertain.

OBJECTIVE
To determine the optimal gestation for birth of twin pregnancies by calculating the week of birth associated with the lowest risk of short- and long-term adverse outcomes (perinatal mortality and special educational need at school)

DESIGN: Population-based data-linkage cohort study
SETTING: Scotland, United Kingdom
PARTICIPANTS: 43,133 twin infants born from 34 weeks onwards between 1980 and 2015.

EXPOSURES
Gestational age at birth in weeks.

MAIN OUTCOMES AND MEASURES
Primary outcomes were extended perinatal mortality and a record of special educational need [one or more of intellectual disabilities, dyslexia, physical or motor impairment, language or speech disorder, autistic spectrum disorder and social, emotional or behavioural difficulties]) at school (4-18 years old). To infer the impact of birth, clinical outcomes of twin infants born at each week of gestation from 34 weeks were compared to twin infants remaining in utero thereafter.

RESULTS
Maternity and education records were available for 43,133 and 9,519 twins respectively. Compared to remaining in utero (n=26,172) birth at any week from 34 to 37 weeks was associated with increased odds of perinatal death (i.e. adjusted [adj.] odds ratio [OR] 1.99, 95% Confidence intervals [CI] 1.53-2.69 at 36 weeks [n=8,056]) and increased risk of special educational need at school (i.e. adj. OR 1.39, 95% CI 1.11-1.74, for birth at 36 weeks compared to 37 weeks). In a competing risks analysis, the risks of stillbirth and neonatal death were balanced at 37 weeks.


CONCLUSIONS AND RELEVANCE
In the absence of a medical complication, twins should not be routinely delivered before 37 completed weeks gestation. Our findings will help optimise shared decision making around the timing of twin birth.