New research has linked the practice of giving antibiotics to some women at risk of premature birth to cerebral palsy and other problems in infants.
The researchers from the University of Leicester in the UK say their findings reaffirm that doctors should not use antibiotics for premature labour when the mother's water is intact and there is no infection.
Their study looked at women at risk of premature labour who had no signs of infection and the researchers say the issue is not the antibiotics but rather the situation in which the antibiotics are given.
The study found 35 cases of cerebral palsy in 769 children of women without early broken waters who were given antibiotics.
This compared with 12 cases among 735 children of women not given the drugs.
Dr. Sara Kenyon who led the study says the findings mean doctors do not need to give antibiotics if a woman's water hasn't broken unless she has an infection.
Dr. Kenyon says smoking, alcohol use and weight problems can increase the chances of premature labour and while it was known children born prematurely are more prone to functional problems later in life, the link to cerebral palsy was unexpected.
The research team team followed up on 9,000 children from the original trial at age 7 using a health questionnaire and national school results to gauge the children's health.
They found that children whose mothers were given the antibiotic erythromycin had an 18% higher risk of mainly mild functional problems that also included struggles with day-to-day problem solving, compared to those whose mothers did not receive the drug.
The antibiotic, co-amoxiclav, did not appear to raise such risk but the researchers say however that unexpectedly, both antibiotics appeared to increase the risk of functional impairment - such as difficulty walking or problems with day to day problem solving - and treble the chance of cerebral palsy in the children of the women whose waters had not broken.
They say though the overall risk was low, why the combination of antibiotics and an intact membrane in women whose water did not burst appeared to affect some children remains unclear.
The researchers believe cerebral palsy is unlikely to be a direct effect of the antibiotic but rather due to factors involved in prolonging a pregnancy that might otherwise have delivered early.
Experts say there is a suspicion that infection is implicated in premature labour and while antibiotics may suppress levels of infection to stop preterm labour, the baby remains in a hostile environment.
Infections during pregnancy or infancy are known to cause cerebral palsy which can cause physical impairments and mobility problems and is caused by the failure of a part of the brain to develop before birth or in early childhood or by brain damage - it affects one in 400 births.
Doctors now recommend antibiotics only for women whose waters have broken prematurely or have an obvious infection.
Medical experts stress that pregnant women should not feel concerned about taking antibiotics to treat infections and say the findings do not mean that antibiotics are unsafe for use in pregnancy.
The study is published in the journal Lancet.