Valbo 1996.

Methods	Randomised controlled trial of hypnosis to support women to stop smoking during pregnancy. Study conducted in Buskerud Central Hospital in Oslo, Norway (Europe), with recruitment from January 1992 to June 1993.
Participants	Inclusion criteria: Women still smoking at 18‐week US visit. Exclusion criteria: Not further specified. Recruitment: Expected numbers of pregnant smokers were 630. 158 (25%) agreed to participate and were randomised (78, I = 80). Baseline characteristics: Mean cigarettes/day prior to pregnancy I = 15.6, C = 15.0; Mean cigarettes per day at 18 weeks' gestation C = 9.7, I = 11.3; Partner smoking C = 73%, I = 71%. Mean age C = 26.5, I = 27.9. Progress + coding: None.
Interventions	Control: "Routine pregnancy health care". Intervention: Anaesthesiologist provided 2 x 45 min sessions at 2‐week interval of a protocol‐based script (Handbook of the American Society of Clinical Hypnosis); the tape played after hypnosis was established emphasised the unpleasant effects of smoking, affirmed her wish to quit, encouraged her will and capacity to quit, and instructed her in meeting cravings with relaxation techniques and self‐hypnosis, explained during the session. Second visit tape was different with more weight on her capacity and taking control. Both tapes avoided "moralizing about her responsibility for pregnancy outcome". Main intervention strategy: Counselling (single intervention) compared to UC. Intensity: Frequency (C = 0, I = 4); Duration (C = 0, I = 3). Intervention provided by dedicated study staff: Efficacy study.
Outcomes	Self‐reported abstinence at birth (late pregnancy*), mean cigarettes per day at birth*, Self‐reported reduction in smoking* (The SD used in the analysis in this review was calculated from a P value = 0.2 given in the paper) and increase at end of pregnancy, Perinatal deaths*.
Notes	Process evaluation did not rate the intervention highly: mean score of 2.05/7.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The numbers from 1 to 100 were set up in random order, and by drawing lot, the women willing to participate were randomised into the intervention or control group.
Allocation concealment (selection bias)	Unclear risk	Women allocated to groups by drawing lots (it was not clear when this took place).
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Of 80 allocated to intervention, 13 did not receive an appointment in time, and 15 did not attend, and were excluded from the analysis.
Selective reporting (reporting bias)	Unclear risk	Only smoking outcomes reported.
Other bias	Unclear risk	No other bias detected.
Biochemical validation of smoking abstinence (detection bias)	High risk	No biochemical validation.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Psychological intervention, authors state that usual caregivers were not aware of group allocation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported.
Incomplete implementation	High risk	28/80 women randomised did not receive the intervention
Equal baseline characteristics in study arms	High risk	Significantly more smokers in intervention group at entry.
Contamination of control group	Low risk	Dedicated hypnotist provided intervention.