Two senior doctors at Coventry and Warwickshire hospital say the current HIV screening system for expectant mothers can fail to detect the virus.
HIV re-screening is now offered to vulnerable expectant mothers
They say two babies in the city were born with HIV last year, despite their mothers initially testing negative.
The doctors say women who are screened for HIV in the early weeks of pregnancy may have been tested at a stage when it could not be detected.
They say women at high risk should now be offered a re-test at 32 weeks.
The claims are made in the current edition of the British Medical Journal.
The doctors say current practices in Coventry have now changed to re-test mothers who are at high risk of contracting HIV and they are urging other primary care trusts to follow suit.