Abstract: This updated review includes 100 trials involving more than 83,246 mother-infant pairs of which 73 studies contribute data (58 individually-randomised trials and 15 cluster-randomised trials). We considered that the overall risk of bias of trials included in the review was mixed. Of the 31 new studies included in this update, 21 provided data for one or more of the primary outcomes. The total number of mother-infant pairs in the 73 studies that contributed data to this review is 74,656 (this total was 56,451 in the previous version of this review). The 73 studies were conducted in 29 countries. Results of the analyses continue to confirm that all forms of extra support analyzed together showed a decrease in cessation of 'any breastfeeding', which includes partial and exclusive breastfeeding (average risk ratio (RR) for stopping any breastfeeding before six months 0.91, 95% confidence interval (CI) 0.88 to 0.95; moderate-quality evidence, 51 studies) and for stopping breastfeeding before four to six weeks (average RR 0.87, 95% CI 0.80 to 0.95; moderate-quality evidence, 33 studies). All forms of extra support together also showed a decrease in cessation of exclusive breastfeeding at six months (average RR 0.88, 95% CI 0.85 to 0.92; moderate-quality evidence, 46 studies) and at four to six weeks (average RR 0.79, 95% CI 0.71 to 0.89; moderate quality, 32 studies). We downgraded evidence to moderate-quality due to very high heterogeneity. We investigated substantial heterogeneity for all four outcomes with subgroup analyses for the following covariates: who delivered care, type of support, timing of support, background breastfeeding rate and number of postnatal contacts. Covariates were not able to explain heterogeneity in general. Though the interaction tests were significant for some analyses, we advise caution in the interpretation of results for subgroups due to the heterogeneity. Extra support by both lay and professionals had a positive impact on breastfeeding outcomes. Several factors may have also improved results for women practising exclusive breastfeeding, such as interventions delivered with a face-to-face component, high background initiation rates of breastfeeding, lay support, and a specific schedule of four to eight contacts. However, because within-group heterogeneity remained high for all of these analyses, we advise caution when making specific conclusions based on subgroup results. We noted no evidence for subgroup differences for the any breastfeeding outcomes. When breastfeeding support is offered to women, the duration and exclusivity of breastfeeding is increased. Characteristics of effective support include: that it is offered as standard by trained personnel during antenatal or postnatal care, that it includes ongoing scheduled visits so that women can predict when support will be available, and that it is tailored to the setting and the needs of the population group. Support is likely to be more effective in settings with high initiation rates. Support may be offered either by professional or lay/peer supporters, or a combination of both. Strategies that rely mainly on face-to-face support are more likely to succeed with women practising exclusive breastfeeding.

Plain-language summary: We searched for evidence on 29 February 2016 and identified a further 31 new trials for inclusion in the review. This updated review now includes 100 randomised controlled studies involving more than 83,246 women. The 73 trials that contributed to the analyses were from 29 countries and involved 74,656 women. Some 62% of the women were from high-income countries, 34% from middle income countries and 4% from low-income countries All forms of extra organised support analyzed together showed an increase in the length of time women continued to breastfeed, either with or without introducing any other types of liquids or foods. This meant that fewer women stopped any breastfeeding or exclusively breastfeeding (moderate quality evidence) before four to six weeks and before six months. Both trained volunteers and doctors and nurses had a positive impact on breastfeeding. Factors that may have contributed to the success for women who exclusively breastfed were face-to-face contact (rather than contact by telephone), volunteer support, a specific schedule of four to eight contacts and high numbers of women who began breastfeeding in the community or population (background rates). The term 'high-quality evidence' means that we are confident that further studies would provide similar findings. No outcome was assessed as being 'high-quality'. The term 'moderate-quality evidence' means that we found wide variations in the findings with some conflicting results in the studies in this review. New studies of different kinds of support for exclusive breastfeeding may change our understanding of how to help women to continue with exclusive breastfeeding. The methodological quality of the studies was mixed and the components of the standard care interventions and extra support interventions varied a lot and were not always well described. Also, the settings for the studies and the women involved were diverse. Providing women with extra organised support helps them breastfeed their babies for longer. Breastfeeding support may be more helpful if it is predictable, scheduled, and includes ongoing visits with trained health professionals including midwives, nurses and doctors, or with trained volunteers. Different kinds of support may be needed in different geographical locations to meet the needs of the people within that location. We need additional randomised controlled studies to identify what kinds of support are the most helpful for women.