Both mothers and fathers should be allowed to make choices that work best for them, the organisation added.
Under current legislation, women expecting a baby are allowed to take a maximum of 52 weeks off work as maternity leave. Of this, 39 weeks are paid and the remainder is unpaid.
Fathers are given two weeks’ leave following the birth of their child and are paid a statutory amount at a flat rate.
The government is now planning to overhaul the existing system to allow both parents to share leave and care for their children between them.
Proposals include giving women 18 weeks off as maternity leave and then letting mothers and fathers decide how to split the remaining 34 weeks between them.
It is hoped that the new system will allow both parents to share the responsibilities of raising a child and will give them an opportunity to find a balance that suits them.
Commenting, Dalia Ben-Galim of the IPPR said that the new policies could “change the flexible work landscape, particularly around maternity and paternity leave”.
“Parental leave schemes need to provide equitable choices for men and women to work and care,” she added.
“The ‘motherhood penalty’ means that the way maternity leave and pay are configured makes a significant difference to the choices women and men make, and the level of pay is critical in this.”
Recently-published figures from the Office for National Statistics show that the number of women claimants of Jobseeker’s Allowance has reached its highest level in the last 15 years.
More than 512,000 women were claiming the benefit last month, the highest number since April 1996.