We included 34 studies, which includes one that was a follow-up study and 20 that were rated as being at high risk of bias. We conducted 14meta-analyses assessing physical outcomes post-intervention.
Nine meta-analyses showed significant findings favouring the intervention group for weight (MD -965.25 g; 95% CI -1360.52 to -569.98), length (MD -1.30 cm; 95%CI -1.60 to -1.00), head circumference (MD -0.81 cm; 95% CI -1.18 to -0.45), arm circumference (MD -0.47 cm; 95% CI -0.80 to -0.13), leg circumference(MD -0.31 cm; 95% CI -0.49 to -0.13), 24-hour sleep duration (MD -0.91 hr; 95% CI -1.51 to -0.30), time spent crying/fussing (MD -0.36; 95% CI -0.52 to -0.19), deceased levels of blood bilirubin (MD -38.11 mmol/L; 95% CI -50.61 to -25.61), and there were fewer cases of diarrhoea, RR 0.39; 95% CI 0.20 to 0.76).
Non-significant results were obtained for cortisol levels, mean increase in duration of night sleep, mean increase in 24-hour sleep and for number of cases of upper respiratory tract disease and anaemia.
Sensitivity analyses were conducted for weight, length and head circumference, and only the finding for length remained significant following removal of studies judged to be at high risk of bias. These three outcomes were the only ones that could also be meta-analysedat follow-up; although both weight and head circumference continued to be significant at 6-month follow-up, these findings were obtained from studies conducted in Eastern countries only. No sensitivity analyses were possible.
We conducted 18 meta-analyses measuring aspects of mental health and development. A significant effect favouring the intervention group was found for gross motor skills (SMD -0.44; 95% CI -0.70 to -0.18), fine motor skills (SMD -0.61; 95% CI -0.87 to -0.35), personal and social behaviour (SMD -0.90; 95% CI -1.61 to -0.18) and psychomotor development (SMD -0.35; 95% CI -0.54 to - 0.15); although the first three findings were obtained from only two studies, one of which was rated as being at high risk of bias, and the finding for psychomotor development was not maintained following removal of studies judged to be at high risk of bias
in a sensitivity analysis. No significant differences were found for a range of aspects of infant temperament, parent-infant interaction and mental development. Only parent-infant interaction could be meta-analysed at follow-up, and the result was again not significant.