According to research published in Lancet Infectious Diseases, the risk for spontaneous preterm birth, having a baby that is small for gestational age, or stillbirth does not increase due to chlamydia infection that is diagnosed before or during pregnancy

Chlamydia trachomatis is one of the most common sexually transmitted infections but reports on the effects of infection on obstetric outcomes are inconsistent.

To investigate, a cohort comprising women of reproductive age from Western Australia were probabilistically constructed and linked to data on chlamydia testing records, preterm births, and other adverse obstetric outcomes.

Records indicated that from 2001 to 2012, 101,558 women age 15 to 38 had a singleton birth. Of these births, 3.9% were preterm, 9.6% were born too small for gestational age, and 0.7% were stillborn.

During pregnancy, at least one chlamydia test was on record for 20.9% of women and 6.4% were positive. Before pregnancy, 18.9% received at least one test and 8.3% of these were positive.

After adjusting for demographic factors, maternal smoking, and previous infection history, no significant associations were found between a positive chlamydia test and spontaneous preterm birth (adjusted odds ratio [aOR] 1.08; 95% CI 0.91-1.28; P =.37), a baby who was small for gestational age (aOR 0.95; 95% CI 0.85-1.07; P =.39), or stillbirth (aOR 0.93; 95% CI 0.61-1.42; P =.74).

Data were not available on cohort treatment, but a 2008 audit of practitioner-notified cases indicated 92% of women were prescribed either azithromycin or doxycycline.

Therefore, it is presumed that positive tests before and during pregnancy in this study were treated. Also, negative outcomes associated with infection severity, symptomatic vs asymptomatic cases and genetic susceptibility to infection remain unknown.

"Findings support the continued screening of high-risk women during pregnancy for chlamydia and should reassure women who have chlamydia diagnosed and treated during pregnancy that there is no increased risk of these serious adverse birth outcomes," concluded the researchers.