Study Links Adverse Childhood Experiences in Firstborns to Mental Health Issues in Siblings

Children are nearly three-quarters (71%) more likely to develop mental health problems between the ages of 5 and 18, if the firstborn child in their family experienced adversity during their first 1,000 days, finds a new study led by UCL researchers.

The study published in The Lancet Public Health found that mothers whose firstborns had experienced adverse childhood experiences had a 71% increased risk of having children with mental health problems, compared to mothers whose firstborn did not experience adversity.

As part of the study, researchers analysed linked GP and hospital health records from 333,048 first-time mothers and their 534,904 children (firstborns and siblings) born in England between 2002 and 2018. They focused on six different forms of adverse childhood experiences in the firstborn child recorded during their first 1,000 days of life (from conception up until the age of two).

These included: child maltreatment, intimate partner violence, maternal substance misuse, maternal mental health problems, adverse family environments (e.g. homelessness), and high-risk presentations of child maltreatment (e.g. unexplained child injuries).

Over a third (37.1%) of firstborn children had at least one recorded adverse childhood experience. The most common adverse childhood experiences were living with maternal mental health problems (21.6%), followed by adverse family environments (14.5%) such as parental criminality and housing instability.

Approximately one in five (19.8%) mothers had at least one child with a recorded mental health problem between the ages of 5 and 18. Mothers whose firstborns experienced adverse childhood experiences had significantly more children with mental health problems (average of 30 per 100 mothers) compared to mothers whose firstborns did not (average of 17 per 100 mothers).

The risk of mental health problems was consistent across all siblings, regardless of birth order (firstborn vs thirdborn), in families where the firstborn experienced adverse childhood experiences. Children in families where the firstborn experienced adversity also had 50% more emergency hospital admissions for any reason and double the amount of mental health-related healthcare contacts.

Reference: Syed. S., et al. (2025) Adverse childhood experiences in firstborns and mental health risk and health-care use in siblings: a population-based birth cohort study of half a million children in England. The Lancet Public Health. doi.org/10.1016/s2468-2667(24)00301-3.