Crowther 1989.

Methods	Randomisation and allocation concealment: the study used block randomisation without stratification to provide balanced numbers in the study groups. Use of consecutively‐numbered, opaque, sealed envelopes. Researchers involved in allocating the women to the treatment groups were not involved in preparing the randomisation schedule. Blinding of outcome assessment: paediatrician examining newborn infants was unaware to which group the mother had been allocated. Documentation of exclusion: no losses to follow‐up.
Participants	139 women with a twin pregnancy and a cervical score of ‐2 or less at or before 34 weeks' gestation attending a special antenatal clinic for multiple pregnancy. Cervical score is length minus dilatation (cm) of the cervix.
Interventions	Women allocated to the intervention group received bed rest in the hospital. Women allocated to the control group continued conventional outpatient management and were only admitted to the hospital if pregnancy complications occurred.
Outcomes	Primary outcomes Gestational age at delivery (using Dubowitz scoring) Preterm birth (< 37 weeks) Small‐for‐gestational age (birthweight < 10th centile by local singleton standards) Seconcary outcomes Very preterm birth (< 34 weeks) Birthweight Perinatal mortality Apgar score of < 7 at 1 min and 5 min Admission to NICU and length of stay Neonatal and maternal morbidities
Notes	Chorionicity: not reported Sample‐size calculation: reported, 44 women for a 40% (from 80%‐40%) reduction of preterm delivery rate at the 5% level Intention‐to‐treat analyses: performed Compliance: 2 women (3%) in the hospitalisation group did not attend the antenatal ward and 17 women (25%) in the control group were admitted to hospital because of pregnancy complications Location: single centre in Harare, Zimbabwe Timeframe: 1984
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Block randomisation without stratification to provide balanced numbers in the study groups. Use of a series of consecutively‐numbered, opaque, sealed envelopes. p 851
Allocation concealment (selection bias)	Low risk	"The researchers involved in allocating the women to the treatment groups were not involved in preparing the randomisation schedule." p 851
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Blinding of participants and personnel was not possible due to the type of intervention (hospitalisation and bed rest compared with no activity restriction at home)
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"All newborn infants were examined by a paediatrician who was unaware to which group the mother had been allocated." p 851
Incomplete outcome data (attrition bias) All outcomes	Low risk	No loss to follow‐up and analysis on an intention‐to‐treat basis
Selective reporting (reporting bias)	Unclear risk	No information provided about trial protocol or predefined outcomes
Other bias	Low risk	The study appears to be free of other sources of bias