Abstract: This updated review includes a total of 25 studies, with outcome data for 11,246 mothers and babies enrolled in 21 studies. We assessed the overall risk of bias of included studies to be low or unclear, mainly because of limited reporting or uncertainty in how randomisation was generated or concealed (which led us to downgrade the quality of most outcomes to moderate), and the impracticability of blinding participants. When compared with routine care, programmes offering additional social support for at-risk pregnant women may slightly reduce the number of babies born with a birthweight less than 2500 g from 127 per 1000 to 120 per 1000 (risk ratio (RR) 0.94, 95% confidence interval (CI) 0.86 to 1.04; 16 studies, n = 11,770; moderate-quality evidence), and the number of babies born with a gestational age less than 37 weeks at birth from 128 per 1000 to 117 per 1000 (RR 0.92, 95% CI 0.84 to 1.01, 14 studies, n = 12,282; moderate-quality evidence), though the confidence intervals for the pooled effect for both of these outcomes just crossed the line of no effect, suggesting any effect is not large. There may be little or no difference between interventions for stillbirth/neonatal death (RR 1.11, 95% CI 0.88 to 1.41; 15 studies, n = 12,091; low-quality evidence). Secondary outcomes of moderate quality suggested that there is probably a reduction in caesarean section (from 215 per 1000 to 194 per 1000; RR 0.90, 95% CI 0.83 to 0.97; 15 studies, n = 9550), a reduction in the number of antenatal hospital admissions per participant (RR 0.78, 95% CI 0.68 to 0.91; 4 studies; n = 787), and a reduction in the mean number of hospitalisation episodes (mean difference −0.05, 95% CI −0.06 to −0.04; 1 study, n = 1525) in the social support group, compared to the controls. Postnatal depression and women's satisfaction were reported in different ways in the studies that considered these outcomes and so we could not include data in a meta-analysis. In one study postnatal depression appeared to be slightly lower in the support group in women who screened positively on the Edinbugh Postnatal Depression Scale at eight to 12 weeks postnatally (RR 0.74, 95% CI 0.55 to 1.01; 1 study, n = 1008; moderate-quality evidence). In another study, again postnatal depression appeared to be slightly lower in the support group and this was a self-report measure assessed at six weeks postnatally (RR 0.85, 95% CI 0.69 to 1.05; 1 study, n = 458; low-quality evidence). A higher proportion of women in one study reported that their prenatal care was very helpful in the supported group (RR 1.17, 95% CI 1.05 to 1.30; 1 study, n = 223; moderate-quality evidence), although in another study results were similar. Another study assessed satisfaction with prenatal care as being "not good" in 51 of 945 in the additional support group, compared with 45 of 942 in the usual care group. No studies considered long-term morbidity for the infant. No single outcome was reported in all studies. Subgroup analysis demonstrated consistency of effect when the support was provided by a healthcare professional or a trained lay worker. The descriptions of the additional social support were generally consistent across all studies and included emotional support, tangible support such as home visits, and informational support. Pregnant women need the support of caring family members, friends, and health professionals. While programmes that offer additional social support during pregnancy are unlikely to have a large impact on the proportion of low birthweight babies or birth before 37 weeks' gestation and no impact on stillbirth or neonatal death, they may be helpful in reducing the likelihood of caesarean birth and antenatal hospital admission.

Plain-language summary: We searched for evidence on 5 February 2018. We identified 21 randomised controlled trials from which 11,246 mother-baby pairs contributed results for this review. Examples of the additional social support include information, home visits, telephone calls and stress management. The overall quality of evidence for most outcomes was moderate. It was not possible to blind women to which group they were in. We found that women who received additional social support during pregnancy may be slightly less likely to have a baby with low birthweight (16 studies, 11,770 babies), or give birth too early (14 studies, 12,282 babies). The number of babies that died around the time of birth was similar for both groups of women (15 studies, 12,091 babies). Women who received the additional social support were, however, probably less likely to be admitted to hospital during their pregnancy (4 studies, 787 women), or to have a caesarean birth (15 studies, 9550 women). Women with additional social support may be less likely to be depressed (1 study, 1008 women). Findings around satisfaction with care were mixed, with one study reporting the support group being more satisfied, whilst another study suggested women in the usual care group were more satisfied. The findings did not appear to be different if the social support was provided by trained lay people or health professionals. Although programmes that offer additional social support during pregnancy are unlikely to prevent the pregnancy from resulting in a low birthweight or early birth, before 37 weeks of pregnancy, they may be helpful in reducing the likelihood of antenatal hospital admissions and the need for caesarean births. Additional social support is not powerful enough to improve the outcomes of the pregnancy during which it is provided, as measured by the outcomes considered in this review. The factors contributing to deprivation require social change in order to bring about improvements in health for mothers and their newborn babies.