Vulnerable female migrants may be putting their health and that of their unborn children at risk by not seeking maternity care because they are afraid of being billed thousand of pounds, a charity has claimed.

A report published by charity Doctors of the World UK found many migrants and asylum seekers feared high costs, being arrested or thrown out of the UK if they tried to access antenatal care, so would avoid doing so until the later stages of their pregnancy.

Under current rules maternity care cannot be refused because it is regarded as “immediately necessary care”, but migrants living in the UK without paperwork can be pursued for costs after receiving treatment.

Doctors of the World UK said the costs can be a deterrent to women and can sometimes lead to them suffering complex problems in childbirth which may have been avoided if they had accessed care earlier or had scans which picked up problems at an early stage.

Lucy Jones, one of the authors of the study, said: “These findings indicate an unacceptable inequality in our health system.

“We must continue to improve access to healthcare for all mothers regardless of their wealth or immigration status.”

Experts said delaying antenatal care can prove more costly for the NHS because problems can become more complex and require more treatment in the latter stages of pregnancy.

Midwives also raised concerns they are being used as “border officials” to determine who is eligible for free NHS care when they should be focused on caring for mothers-to-be.

Cathy Warwick, the chief executive of the Royal College of Midwives, said: “We have real concerns that the aggressive pursuit of charging migrant women for medical care may deter them from accessing maternity care. I fear that these women could fall through the cracks and only find their way into the health system when it is too late – if at all.

“Women from these groups are often already in poorer health, have poor pregnancy outcomes and these steps could have negative consequences for their health.

“Our view is very clear. Midwives should not act as gatekeepers to the maternity services. They owe a duty of care to all pregnant women who seek care from them and, they should provide care to all pregnant women irrespective of the woman’s ability to pay.

“We urge service providers to exercise compassion and sensitivity when dealing with migrant women, especially when they have suffered the tragic loss of their baby.”

Doctors of the World UK spoke to 35 users of their east London clinic, and found two thirds of expectant mothers had not accessed maternity care until their second trimester. Most women in England access healthcare in their first trimester.

The charity found some mothers were billed thousands of pounds, even after their baby had died.

In 2013, the charity Maternity Action found that pregnant migrants were putting their lives at risk by disappearing from antenatal care to give birth at home because they couldn’t afford maternity care charges. It found that charging rules are interpreted differently by different hospitals.