I have been asked to reply on behalf of the Department for Business, Innovation and Skills.
There is a range of data in this area, from both Government and academic sources. The BIS-DWP Maternity and Paternity Rights and Women Returners survey series provides evidence on mothers' post-birth employment outcomes.
The Department has also consulted widely with employer, family and women's representative groups as part of the consultations on introducing shared parental leave, including on the impact on women's work experiences of pregnancy and maternity leave.
Data from the two most recent Maternity and Paternity Rights Surveys suggest that:
the majority of mothers return to work; of those who return, the majority return to the same hourly pay range as they had prior to birth;
About half of mothers who had previously worked full-time returned to full-time work; nine out of 10 mothers who had supervisory responsibilities before the birth of their child continued to do so after.
The survey also provides information on why women do not return to work.
the difference in employment rates between men and women increases after the birth of a child, and takes some time to recover; the average pay gap between men and women rises after the birth of a child and doesn't fully recover.
The situation for women is improving, however. LFS data show that women's employment rate is rising over time, while ONS' Statistical Bulletin on the Annual Survey of Hours and Earnings shows the gender pay gap to be falling.