Mums in England face a "substantial and long-lasting reduction" in earnings after having children, according to new findings from the Office for National Statistics (ONS).
Five years after having their first child, mums' earnings drop by an average of £1,051 a month compared with their salary one year before having a child.
Mums' earnings continue to be affected after the births of second and third children.
Rachel Grocott, chief executive of campaign group Pregnant Then Screwed, called the findings "completely abhorrent" and said the impact of the motherhood penalty is "not just unfair - it's avoidable".


