Most studies on the effect of pregnancy intentions on mothers’ and children’s wellbeing cannot separate the effect of pregnancy intention status from the socio-demographic characteristics associated with it. There is a lack of studies on the topic in low and middle-income countries (LMICs) taking a multi-country comparative perspective. We analyse 59 Demographic and Health Surveys to examine the effect of pregnancy intentions on child mortality, low birth weight and place of delivery using sibling fixed-effects models to control for confounding due to unobserved family socio-demographic characteristics. Results show unwanted/mistimed children have a higher risk of mortality in 36 countries, low birth weight in 10, and lower likelihood of delivery in a health facility in 6. To the best of our knowledge, this is the first study to analyse the effect of pregnancy intention status on mother and child outcomes using a cross-country comparative setting in LMICs and fixed effects models.