Brooke Tasovac​ thought she had done everything right. Before trying to conceive a second child she added pregnancy to her existing hospital policy, which required her to serve a nine-month waiting period.

So she was shocked when – still in her hospital bed recovering from an emergency caesarean – she was told Australian Unity wouldn't be covering the operation because she had given birth to Amy at eight months and 21 days.

"I had no choice. It was an emergency medical procedure because she had to come out a bit earlier for her own safety," said Ms Tasovac, from Sydney's north-west.

"They may have a leg to stand on legally, but not ethically and not from a customer service point of view. Nobody ever said to me: 'If your baby is born early, you're not covered'."

In its latest industry communique, the Private Health Insurance Ombudsman chastised health funds for giving the wrong information or not being clear enough about the waiting periods for obstetrics – whether it applies to the mother's hospital admission or the expected delivery date.

It said investigations into the 51 complaints made in the past year found several stemmed from salespeople providing the wrong information over the phone.

The waiting period for obstetrics is generally 12 months.

"There appears to have been some confusion about whether the insurer would offer flexibility to mothers whose babies are born a week or two earlier than anticipated," it said.

"The advice from insurers to the Ombudsman was that in all instances the waiting period of 12 months for obstetrics applies, even to cases where a baby is born only a couple of days before the end of the waiting period."

The Ombudsman urged health funds to advise prospective mothers well ahead of time that regardless of the circumstances, it will not offer any flexibility if the baby is born earlier than expected.

Ms Tasovac said she was not informed that the policy would offer no flexibility in the event of a premature birth.

The photography events manager had upgraded her policy so she could be a private patient in a public hospital. She wanted the same obstetrician throughout her pregnancy because of her experiences of miscarriage.

A few months in she was diagnosed with placenta previa​, meaning she would have to give birth by caesarean section.

In the past, health insurers were willing to use the expected delivery date, as stated by a doctor, to determine whether the waiting period had been met. This practice is now very rare.

When Ms Tasovac shared her predicament on Facebook group Ryde District Mums, another member commented she was aware of a recent case where Bupa had offered two weeks' flexibility.

Ms Tasovac, a mother also to Ella, aged four, now faces unexpected hospital bills of up to $1300.

"I felt panic and real anger that somebody could be so unsympathetic to our situation," she said.

"I basically paid an extra $200 every single month for the last nine months for absolutely nothing."

An Australian Unity spokesman said it regretted causing Ms Tasovac any distress and would work with her to reach a positive outcome.

"Australian Unity takes great care to ensure waiting periods and how these apply are clearly explained to our members, particularly those relating to pregnancy," he said.

"Policy terms are applied for the protection of all members and to ensure premiums remain affordable."

The Ombudsman receives on average 45 complaints about the 12-month waiting period for obstetrics and 13 complaints about benefits payable for newborns each year.