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Chlamydia trachomatis and the risk of spontaneous preterm birth, babies who are born small for gestational age, and stillbirth: a population-based cohort study

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Summary

Background

Chlamydia trachomatis is one of the most commonly diagnosed sexually transmitted infections worldwide, but reports in the medical literature of an association between genital chlamydia infection and adverse obstetric outcomes are inconsistent.

Methods

The Western Australia Data Linkage Branch created a cohort of women of reproductive age by linking records of birth registrations with the electoral roll for women in Western Australia who were born from 1974 to 1995. The cohort was then linked to both chlamydia testing records and the state perinatal registry for data on preterm births and other adverse obstetric outcomes. We determined associations between chlamydia testing, test positivity, and adverse obstetric outcomes using multivariate logistic regression analyses.

Findings

From 2001 to 2012, 101 558 women aged 15 to 38 years had a singleton birth. Of these women, 3921 (3·9%) had a spontaneous preterm birth, 9762 (9·6% of 101 371 women with available data) had a baby who was small for gestational age, and 682 (0·7%) had a stillbirth. During their pregnancy, 21 267 (20·9%) of these women had at least one chlamydia test record, and 1365 (6·4%) of those tested were positive. Before pregnancy, 19 157 (18·9%) of these women were tested for chlamydia, of whom 1595 (8·3%) tested positive for chlamydia. Among all women with a test record, after adjusting for age, ethnicity, maternal smoking, and history of other infections, we found no significant association between a positive test for chlamydia and spontaneous preterm birth (adjusted odds ratio 1·08 [95% CI 0·91–1·28]; p=0·37), a baby who was small for gestational age (0·95 [0·85–1·07]; p=0·39), or stillbirth (0·93 [0·61–1·42]; p=0·74).

Interpretation

A genital chlamydia infection that is diagnosed and, presumably, treated either during or before pregnancy does not substantially increase a woman's risk of having a spontaneous preterm birth, having a baby who is small for gestational age, or having a stillbirth.

Funding

Australian National Health and Medical Research Council.

Introduction

Worldwide, chlamydia is one of the most common sexually transmitted infections, with an estimated 131 million new cases annually.1 Although genital infections are thought to contribute to the incidence of adverse obstetric outcomes such as spontaneous preterm birth and stillbirth,2 there are insufficient data regarding the role of chlamydia infections in these outcomes. To our knowledge, there are no published randomised controlled trials of the effects of chlamydia screening in pregnancy on obstetric outcomes.3 Furthermore, randomised placebo-controlled prevention trials of antibiotics (including azithromycin) given during the antenatal period to high-risk women have found no effect on the incidence of preterm birth.4 Findings from observational studies have been inconsistent: most studies5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 but not all16, 17, 18, 19, 20, 21, 22 suggest that chlamydia infection increases the risk of preterm birth. There is similar discordance in studies examining the effects of chlamydia infection on birthweight and stillbirth.9, 23

There are many possible explanations for the discrepancy in findings between published observational studies. These explanations include small numbers of events in these studies, which might have led to random error; inconsistency in the type of chlamydia test used (serology, culture, or nucleic acid amplification); variations in the outcome definition and ascertainment; use of case-control designs in which control populations might not be well matched; inadequate control of potential confounders, including other genital tract infections or other factors known to result in adverse obstetric outcomes, such as smoking during pregnancy; and the potential for publication bias. In this analysis, we used a large cohort of women with records of laboratory chlamydia tests and test positivity, and we used reliable ascertainment of obstetric outcomes to examine the effects of chlamydia infection on the risk of spontaneous preterm birth and other adverse birth outcomes.

Section snippets

Study design and population

A cohort comprising women of reproductive age residing in the Australian state of Western Australia (WA) was constructed by probabilistically linking two whole-population administrative datasets: birth registrations, which contain a record of all children born and registered in WA from 1974 onwards, and the WA electoral roll. Electoral enrolment is compulsory for Australian citizens, with an estimated 92% of the eligible population included on the roll in WA.24 Eligible women were all those

Results

We identified 101 558 women aged 15 to 38 years in the cohort with a first record of a singleton birth between 2001 and 2012. Of births that could be classified, 3921 (3·9%) of 101 558 women had a spontaneous preterm birth, 9762 (9·6%) of 101 371 births were small for gestational age, and 682 (0·7%) of 101 558 infants were stillborn (table 1).

Table 1 shows the characteristics of the mothers, grouped according to obstetric outcomes. Generally, women with each of the adverse obstetric outcomes

Discussion

This large population-based cohort study analysed more than 20 000 women with laboratory testing data on chlamydia positivity during pregnancy. In more than 900 spontaneous preterm births and more than 2500 babies who were small for gestational age, we found no increase in the risk of having a spontaneous preterm birth or a baby that was small for gestational age among women with a positive chlamydia test during pregnancy. Although there were fewer cases, we also found no evidence to suggest an

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