A Cochrane review [Abstract] 1 included 88 studies with over 28 000 subjects providing data on smoking abstinence in late pregnancy. Interventions were categorised as counselling, health education, feedback, incentives, social support, exercise and dissemination. In separate comparisons, there is high-quality evidence that counselling increased smoking cessation and abstinence in late pregnancy compared with usual care T1 and less intensive interventions (18 studies; average RR 1.25, 95% CI 1.07 to 1.47). A clear effect was seen in smoking abstinence in postpartum T2. Women who received psychosocial interventions had a 17% reduction in infants born with low birthweight, a significantly higher mean birthweight, and a 22% reduction in neonatal intensive care admissions T2.
| Interventions and comparisons | Relative effect(95% CI) | Risk with comparison | Risk with main intervention (95% CI) | №of participants(studies) Quality of evidence |
|---|---|---|---|---|
| Counselling vs usual care | RR 1.44(1.19 to 1.73) | 9 per 100 | 13 per 100(11 to 16) | 12 432(30) High |
| Health education vs usual care | RR 1.59 (0.99 to 2.55) | 8 per 100 | 12 per 100(8 to 20) | 629(5) Moderate |
| Feedback vs usual care | RR 4.39(1.89 to 10.21) | 4 per 100 | 17 per 100(7 to 39) | 355(2) Moderate |
| Incentives vs alternative interventions | RR 2.36(1.36 to 4.09) | 16 per 100 | 37 per 100(21 to 64) | 212(4) High |
| Exercise vs usual care | RR 1.20(0.72 to 2.01) | 6 per 100 | 8 per 100(5 to 13) | 785(1) Moderate |
| Social support vs less intensive interventions | RR 1.21(0.93 to 1.58) | 19 per 100 | 23 per 100(18 to 31) | 781(7) High |
| Outcome | Relative effect(95% CI) | Risk with control | Risk with Interventions (95% CI) | №of participants(studies) Quality of evidence |
|---|---|---|---|---|
| Abstinence in late pregnancy: self-reported and biochemically validated | RR 1.35(1.23 to 1.48) | 12 per 100 | 16 per 100(15 to 18) | 26 637(97) Moderate |
| Abstinence at 0 to 5 months postpartum | RR 1.32(1.17 to 1.50) | 131 per 1000 | 173 per 1000(153 to 196) | 8366(35) High |
| Low birthweight (under 2500 g) | RR 0.83(0.72 to 0.94) | 92 per 1000 | 76 per 1000(66 to 87) | 9402(18) High |
| Preterm birth (under 37 weeks) | RR 0.93(0.77 to 1.11) | 72 per 1000 | 67 per 1000(55 to 80) | 9222(19) High |
| Mean birthweight (g) | - | The mean birthweight (g) was 0 | MD 55.60 higher(29.82 higher to 81.38 higher) | 11 338(26) High |
| NICU admissions | RR 0.78(0.61 to 0.98) | 118 per 1000 | 92 per 1000(72 to 116) | 2100(8) High |
An individual participant data meta-analysis 2 assessing changes in smoking during pregnancy and risk of adverse birth outcomes included 229 158 singleton births (28 cohorts in Europe and North America). Children from mothers who continued smoking during pregnancy had higher risks of preterm birth (OR 1.08, 95% CI 1.02 to 1.15, P value = 0.012), small size for gestational age (OR 2.15, 95% CI 2.07 to 2.23, P value < 0.001), and childhood overweight (OR 1.42, 95% CI 1.35 to1.48, P value < 0.001). Mothers who reduced the number of cigarettes between the first and third trimester, without quitting, still had a higher risk of small size for gestational age. However, the corresponding risk estimates were smaller than for women who continued throughout pregnancy. Reducing the number of cigarettes during pregnancy did not affect the risks of preterm birth.
A dose-response analysis 3 assessing smoking and the risk of preterm birth included 25 million mother-infant pairs. Maternal smoking during pregnancy was associated with an increased risk of preterm delivery. The adjusted ORs (95% CI) of preterm birth for mothers who smoked 1-2, 6-9, 10-19, and ≥20 cigarettes per day during the first trimester compared with mothers who did not smoke were 1.31 (1.29 to 1.33), 1.33 (1.31 to 1.35), 1.44 (1.43 to 1.45), and 1.53 (1.52 to 1.55), respectively (all P values < 0.001), whereas for those who smoked during the second trimester, the corresponding ORs were 1.37 (1.35 to 1.39), 1.36 (1.34 to 1.38), 1.48 (1.47 to 1.49), and 1.59 (1.58 to 1.61), respectively (all P values < 0.001). Furthermore, smokers who quit before pregnancy, regardless of smoking intensity, had a comparable risk of preterm birth with nonsmokers, although this was not the case when cessation occurred in the first or second trimester of pregnancy.
Date of latest search: 2020-10-28
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