Chlamydia is a sexually transmitted infection which, if a mother has it during pregnancy and labour, can cause eye or lung infections in the newborn baby. The risk of transmission during birth varies, but is about 20% to 50% for eye infections and about 10% to 20% for infection of the lungs. Mothers may also be at increased risk of infection of the uterus. The review looked at various antibiotics being used during pregnancy to reduce these problems and to assess any adverse effects. Tetracyclines taken in pregnancy are known to be associated with teeth and bone abnormalities in babies, and some women find erythromycin unpleasant to take because of feeling sick and vomiting. The review found eleven trials, involving 1449 women, on erythromycin, amoxycillin, azithromycin and clindamycin, and the overall trial quality was good. However, all the trials assessed 'microbiological cure' (that is they looked for an eradication of the infection) and none assessed whether the eye or lung problems for the baby were reduced. Also, none of the trials were large enough to assess potential adverse outcomes adequately. The review found amoxycillin was an effective alternative to erythromycin but lack of long-term assessment of outcomes caused concern about its routine use in practice. If erythromycin is used, some women may stop taking it because of adverse effects. Azithromycin and clindamycin are potential alternatives. More research is needed.