Methods: We systematically reviewed observational studies investigating effects of parental migration on nutrition, mental health, unintentional injuries, infectious disease, substance use, unprotected sex, early pregnancy and abuse among left-behind children aged 0-19 years in LMICs. We searched databases including MEDLINE, EMBASE and CINAHL from inception to 27 April 2017, without language restrictions. We used meta-analyses to pool findings, and subgroup analyses and meta-regression to investigate heterogeneity. A revised version of the Newcastle-Ottawa tool was used to assess bias. The protocol was registered with PROSPERO (CRD42017064871).
Findings: 111 studies were included with outcomes for 264,967 children. 91 studies were conducted in China and focused on effects of internal labour migration. Compared to children of non-migrants, left-behind children had increased risk of depression and higher depression scores (risk ratio (RR) 1·52 [95% confidence interval 1·27-1·82]; standardised mean difference (SMD) 0·16 [0·10-0·21]), anxiety (RR 1·85 [1·36-2·53]); SMD 0·18 [0·11-0·26]), suicidal ideation (RR 1·70 [1·28-2·26]), conduct disorder (SMD 0·16 [0·04-0·28]), substance use (RR 1·24 [1·00-1·52]), wasting (RR 1·13 [1·02-1·24]) and stunting (RR 1·12 [1·00-1·26]). We found no difference for other nutrition outcomes, unintentional injury, abuse or diarrhoea. No studies reported outcomes for other infectious diseases, self-harm, unprotected sex or early pregnancy.
Interpretation: Parental migration is detrimental to left-behind child and adolescent health, with no evidence of any benefit, and the strongest evidence for China. Action is needed by policy-makers and healthcare professionals to improve the health of these young people.