In Discussion Paper No. 1408, Shirley Dex, Heather Joshi, Andrew McCulloch and Susan Macran set out to disentangle various factors influencing whether and how long a mother stays in the labour market/home. They use the 1958 National Child Development Study to trace employment histories and other month-by-month information from the date of the mother’s first birth to age 33.

It is shown that late motherhood is associated with a cluster of individual characteristics which tend to give highly-educated mothers labour market advantages. This suggests that delayed childbearing is not itself crucial. While the age of the youngest child was the paramount predictor of women's employment in previous studies using post-war data, the women's earning power here appears to be of equal importance. There is little evidence to suggest that higher husbands' income inhibits wives' participation. A good education and maintaining close contacts to the labour market by taking no more than maternity leave at the time of the first birth were essential. The results of this study suggest that educational qualifications are more important than the timing of the first birth in securing women’s job continuity and greater benefits in the labour market. But if low-waged women try to emulate the delayed childbirth strategy, they appear to have the worst chances of employment. Certainly they do significantly worse than similar low-waged women who had their children as teenagers or in their early twenties. Inequalities between mothers have increased.

Women's Employment Transitions Around Childbearing
Shirley Dex, Heather Joshi, Andrew McCulloch and Susan Macran