A recent study by researchers at Macalester College, Minnesota, and the University of California, has revealed that the performance of children was found to be good when their mums stayed home for the first year.
Children of mothers who resume work during their first year of life end up faring worse in formal exams and show signs of being more disruptive, reports the Daily Mail.
The child's success was particularly affected if the mother's work was full-time, the study spanning five decades found.
The impact also varied dramatically according to class and whether the child was in a single-parent or two-parent household.
Children of middle-class and two-parent families were more likely to be affected negatively than those from working-class or single-parent families, according to the research.
"Somewhat later employment (years two and three) appeared to be advantageous for children's achievement," it concluded.
Working full-time during a child's first year - rather than reduced hours or not at all - may increase the risk of a child developing behavioural problems, it also emerged.
The research was publicised yesterday by the Daycare Trust charity, which campaigns for affordable childcare and has called for mothers to be given a year's paid parental leave.