Maternity leave cuts household incomes by 30%, putting 58% of families into debt and forcing a fifth of new mums back to work early.
With statutory pay of £138.18 a week, uSwitch has found that families are taking on an average debt of £2,012 during maternity leave.
The switching website found that 11% of new mums return to work early from maternity leave to pay off their debts.
Such is the extent of the financial squeeze, on average families are waiting three years later than planned to have children, added the site.
Meanwhile, from today (Monday 1 December), new rules come into force allowing both parents to share up to 50 weeks of paternity leave, and 37 weeks of statutory pay, between them.
Flexibility when it comes to sharing the mother's maternity leave and pay during a child's first year will apply to couples with babies due or children matched or placed for adoption on or after 5 April 2015.
Mums will still have to take at least two weeks of maternity leave immediately after the birth, with both parents able to choose to share the remaining entitlement of leave and pay between them.
As many as 285,000 working couples are expected to be eligible to share time off from April, according to the government.
Ann Robinson, director of consumer policy at uSwitch.com, said: "The drop in income while on maternity leave can be crippling for families, particularly as one third of working mothers are the main breadwinner. The Shared Parental Leave legislation has the potential to alleviate some of the difficulties faced by parents, but it's going to take a major awareness drive by the government, not to mention a significant cultural shift in the workplace, for it to start having an impact."
She added: "There is still a lot of work to be done to ease the strain on new parents, but in the meantime, families can help themselves by taking a long hard look at their household budgets to see where they can cut costs.
"Short-term debt solutions may seem an efficient way to fund spending, but they can also lead to long-term debt if not managed properly."