Haghighi 2005.

Methods	Randomised by sequential use of opaque, sealed envelopes numbered using random‐number tables. Double blinding implied. No power calculation. No intention‐to‐treat analysis.
Participants	Iran. 150 pregnant women in preterm labour (defined as more than 8 uterine contractions per hr that lasted longer than 30 seconds and progressive cervical dilatation z1 cm during a 3.5‐h observation) between 33 and 36 weeks with a singleton pregnancy.
Interventions	1. Isosorbide dinitrate sublingual tablet 5 mg, repeated every 30 minutes up to 40 mg or stop of contractions. 10 mg 1 hour after halt of contractions and every 6 hrs for 48 hrs (n = 75). 2. Placebo (n = 75).
Outcomes	Primary outcome was preterm birth. Secondary outcomes were adverse effects and Apgar scores.
Notes	Both groups first administered 50 mg i.v. of meperidine in 500 mL of Ringer solution over 30 minutes, followed by 100 mL per hr of the same for 3 hrs. No information on whether women got steroids and/or antibiotic therapy.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random‐number tables.
Allocation concealment (selection bias)	Low risk	Envelopes sequentially numbered, sealed and opaque.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants blinded, unclear re personnel.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Unclear whether assessors blinded or not.
Incomplete outcome data (attrition bias) All outcomes	High risk	Of the 81 women randomised to isosorbide dinitrate group, 6 were excluded for reasons that may have related to treatment allocation (hypotension).
Selective reporting (reporting bias)	Unclear risk	Insufficient information to permit a judgement.
Other bias	Unclear risk	Little information on participant characteristics.