Pregnant women with a history of sexually transmitted infections (STIs) have a higher risk of stillbirth and premature birth - even if they suffered them prior to conception, research suggests.
Chlamydia and gonorrhoea during pregnancy are already linked to complications but now researchers believe infections in the past may also have an impact.
Both STIs are on the rise across England, with chlamydia accounting for 46% of all new STI diagnoses in 2012 (206,912 cases).
Gonorrhoea cases have jumped 21% in one year, to 25,525 cases.
For the new study, experts from the University of New South Wales and the University of Sydney examined data for more than 350,000 women who had their first baby between 1999 and 2008.
Of the group, 3,658 had at least one chlamydia infection before the birth, with 80% of these cases diagnosed before conception.
Some 196 women in the group had been diagnosed with gonorrhoea before the birth, with just under 85% of cases diagnosed before conception.
Half of those diagnosed with gonorrhoea had also previously been infected with chlamydia.
Overall, 4% of the women had an unplanned premature birth, 12% had babies who were small for dates and 0.6% (2,234) of the babies were stillborn.
Even after taking into account factors such as age, social disadvantage, smoking, and conditions such as diabetes and high blood pressure, women who had had a prior infection with either chlamydia or gonorrhoea were still at heightened risk.
Women who had had chlamydia were 17% more likely to have an unplanned premature birth and 40% more likely to have a stillborn baby, the results showed.
Meanwhile, those who had had gonorrhoea were more than twice as likely to have a premature birth.
For women previously diagnosed with chlamydia, the risk of an unplanned premature birth did not differ between those diagnosed more than a year before conception, within a year of conception, or during pregnancy.
Writing online in the journal Sexually Transmitted Infections, the authors said their findings do not prove a direct cause between infections and pregnancy complications.
But they added: “Our results suggest that sexually transmissible infections in pregnancy and the preconception period may be important in predicting adverse obstetric outcomes.”8)