The lender suggested that she get a co-signer  her husband is a graduate student, so his income was not enough to qualify  or reapply after she returned to work. But with the help of a representative from her real estate brokerage firm, Redfin, Dr. Budde was finally able to explain that she was receiving her full salary during her time off since she was using accumulated sick and vacation days. Once she provided a letter from her employer, proving her case, she was able to requalify.

“The reason we were buying the house was because we were having a baby,” said Dr. Budde, who is now living in the three-bedroom home, bought for $300,000. “And now we got punished for having a baby.”

Janis Smith, a spokeswoman for Fannie Mae, said there was nothing in its guidelines that would prohibit a borrower on maternity or paternity leave from qualifying for a mortgage, as long as the borrower had proof at the time of the closing that his or her income would be adequate upon returning to work. Letters from a doctor (with a return date) and the employer (stating the return date and salary) should be enough, she added.

Loans backed by the Federal Housing Administration follow a similar protocol. Brad German, a spokesman for Freddie, said its guidelines required underwriters to make sure the borrower’s income was stable and could be expected to continue for at least three years.

But, brokers said, many lenders are clearly reading those guidelines through an increasingly conservative lens. “Lenders are picking and choosing what part of the Freddie and Fannie guidelines they want to use and how they will interpret them because one bad loan could put a company out of business,” said Jeffrey J. Jaye, president of the Upfront Mortgage Brokers Association, a trade group for brokers who disclose their fees upfront.

For some lenders, that may mean approving a loan only after the borrower is back at work “There is no real assurance that the new mom will come back to work after she has the baby,” said Marc Savitt, president of the Mortgage Center, a brokerage in Martinsburg, W.Va. “It’s just prudent underwriting to go ahead and approve the loan, but she has to be back before closing.” (Lenders cannot ask a woman if she is pregnant, brokers said, but they can ask borrowers if they expect their employment or income situation to change.)

Indeed, if Fannie or Freddie learn that a loan does not meet its underwriting requirements, it can require the lender to repurchase the loan. Both companies are performing more quality control checks on the loans they buy or package and sell as securities. And, perhaps not surprisingly, the number of repurchase requests has risen sharply.