Pettila 1999.

Study characteristics
Methods	RCT
Participants	107 women were randomised. Setting: 8 centres in Finland. Study dates: February 1994 to February 1997. Inclusion criteria: 18 years or older, week 0 to 19 of gestation, any of: (a) previous PE or VTE above knee before current pregnancy; (b) PE or VTE during current pregnancy; (c) previous VTE below knee in association with protein C or protein S deficiency, activated protein C resistance, pregnancy or contraceptive pills. Exclusion criteria: any of the following: surgical procedure within 1 week, surgical procedure in central nervous system, eye or ear within 1 month, intracerebral bleeding within 1 year, platelet count < 100 X 10E9/L twice, hypertension over 150/100 mmHg, S‐creatinine over 155 μmol/L, liver disease, septic endocarditis, known hypersensitivity to heparin, known positive HIV or hepatitis B or C, unsuitable for venous sampling, antithrombin deficiency, artifical hear value, placenta praevia or ablation detected, participation in another study, weight < 45 kg before pregnancy, use of acetylsalicylic acid of any strength.
Interventions	Group 1 (n = 51): subcutaneous LMWH dalteparin (fragmin) once daily (starting dose 5000 IU (women weighing < 85 kg) or 7500 IU (women weighing ≥ 85 kg), dose adjusted based on anti‐Xa measurements). During birth, 2500 IU dalteparin was administered 18 hours after the previous dose if the woman had not yet delivered; if she delivered within 18 hours, 5000 IU was given, 24 hours after the previous injection. The daily dose postpartum was 2500 IU lower than during the third trimester; and 2 weeks after birth, if anti‐Xa was < 0.20, the dose was increased by 2500 IU. Group 2 (n = 56): subcutaneous UFH (7500 IU, adjusted according to APTT target values) twice daily. At the time of birth, and on the first day postpartum 7500 IU UFH was given at 12 hour intervals, and then according to APTT target values. All women: treatment started before week 20 of gestation and continued for 6 weeks after birth.
Outcomes	Review outcomes reported: symptomatic thromboembolic events; symptomatic PE; symptomatic DVT; blood transfusion; bleeding episodes (reports injection‐site haemato mas, bleeding during birth, other bleeding); adverse events sufficient to stop treatment; symptomatic osteoporosis; fetal loss (reports spontaneous abortion); thrombocytopenia. Other outcomes reported: lumbosacral compression fractures, fetal outcomes, laboratory values (Hb, platelet count, serum creatinine, serum alanine aminotransferase); birth bleeding (mL); caesarean section; birthweight; Apgar score.
Notes	Funding sources: supported by research funds from Helsinki University Central Hospital and a grant from Pharmacia and Upjohn. Declarations of interest: not reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation quote: "by means of a computer generated procedure".
Allocation concealment (selection bias)	Low risk	Quote: "Immediately after the inclusion and exclusion criteria were met and informed consent was obtained, a closed envelope was opened"; the randomisation list was kept outside the centres.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Open design (not feasible).
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No detail of blinding of outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	2 randomised participants (1 from each group) received no prophylactic treatment before discontinuation of the study because of withdrawal of consent and were excluded from the analysis. Thus 105 participants (50 from the dalteparin and 55 from the heparin group) were included in the intention‐to‐treat analysis.
Selective reporting (reporting bias)	Unclear risk	No trial protocol to confidently assess selective reporting.
Other bias	Low risk	No other obvious risk of bias identified.