Objectives Multiple pregnancies in the UK are monitored intensively which may identify concerns with the growth or biophysical profile of one twin necessitating delivery. Our aim was to compare the outcomes of pre-term twins in such situations.

Methods A retrospective observational study of all multiple pregnancies <37 weeks gestation in a single tertiary centre between 1st October 2001 and 30th November 2006 (5 yrs). Analysis was in 3 groups depending upon whether delivered early due to: 1. Concern about one twin 2. Spontaneous labour 3. Concern for mother or both twins.

Sibling outcomes were compared in terms of ventilatory and cardiovascular support in all 3 groups.

Results Data was collected for all 165 multiple pregnancies during the study period with 60 in group 1, 69 in group 2 and 36 in group 3.

In group 1 the twin without antenatal concerns required significantly more respiratory support than its sibling (34 vs 22 babies) OR 0.44, 95% CI 0.214 to 0.917 and also more cardiovascular support (6 vs 2 babies) but this did not achieve significance.

Among babies in group 1 who needed respiratory support, the twin without antenatal concerns needed significantly longer duration of ventilation (mean 10.98 vs 3.3 days, p<0.05)

The other 2 groups did not show any significant differences.

Conclusions This study demonstrates, for the first time, that in twins delivered prematurely due to antenatal concern about one baby, the other baby is more likely to need respiratory support postnatally. Antenatal counselling should take this into account.