Beta We are building this new website to better deliver information. Learn more about this site.
Pregnancy Care Guidelines

40 Chlamydia

Chlamydia is a common sexually transmitted infection that can cause long-term complications and, in pregnancy, may cause adverse maternal and neonatal outcomes. Antenatal care provides opportunities for testing women from population groups with a high prevalence of the infection.

40.1 Background

Chlamydia is caused by the bacterium Chlamydia trachomatis. Genital chlamydial infection remains asymptomatic in at least 70% of women and most infections probably clear spontaneously without morbidity (Geisler et al 2008; Rogers et al 2008). Complications that may arise for women include chronic pelvic pain, pelvic inflammatory disease, infertility and ectopic pregnancy.

40.1.1 Prevalence of chlamydia

  • Rates of diagnosis: Chlamydia is the most frequently reported notifiable condition in Australia. The notification rate for chlamydia increased steadily between 2007 and 2011, remained relatively stable between 2011 and 2015 and increased by 8% in 2016 (The Kirby Institute 2017b). Notifications have been higher in women than in men in all years (457.6 vs 364.3 per 100,000 in 2016). The rate of notification in the Aboriginal and Torres Strait Islander population has remained relatively stable since 2012 but in 2016 was more than three times that in the nonIndigenous population (1,193 vs 419 per 100,000) (The Kirby Institute 2017a).
  • Age: The trends in notification rates vary by age group. Among women, rates in the 15–19 year age group have declined (from 2,415 in 2011 to 1,932 per 100,000 in 2016), rates in the 20–24 year age group have remained relatively stable (2,265 in 2011 and 2,399 in 2016) and rates in the 25–29 year age group increased steadily between 2006 and 2016 (from 644 to 1,086 per 100,000) (The Kirby Institute 2017b). The chlamydia notification rate in Aboriginal and Torres Strait Islander women aged 15–19 and 20–29 years in 2016 was four times and three times higher, respectively, than in the non-Indigenous population (The Kirby Institute 2017a).
  • Geographical distribution: After a steady increase in notifications between 2007 and 2011 in all jurisdictions, between 2012 and 2016 chlamydia notification rates were more stable, except in Queensland, where there was a steady increase (from 410.7 to 480.4 per 100,000). Chlamydia notification rates rose between 2015 and 2016 in New South Wales (14%) and Western Australia (7%) (The Kirby Institute 2017b). Between 2012 and 2016, notification rates were highest and remained stable in remote and very remote regions (806.6 per 100 000 in 2016). Notification rates also remained stable in major cities in the same period (327.0 per 100 000 in 2016) but declined by 13% in inner and outer regional areas (419.5 to 367.2 per 100 000) (The Kirby Institute 2017b). A similar pattern was seen in both males and females but in females there was a larger decline in inner and outer regional areas (16%) and rates also declined (11%) in the major cities.

Data on diagnoses of chlamydia are incomplete and may provide a distorted view of population rates in Australia. Differences in rates of diagnosis between areas and populations may reflect a range of factors, including variations in approaches to offering testing, access to services, and recording of Indigenous status.

40.1.2 Risks associated with chlamydia in pregnancy

Chlamydia infection during pregnancy has been associated with adverse outcomes including higher rates of preterm birth (OR 1.6; 90% CI 1.01–2.5) and intrauterine growth restriction (OR 2.5; 90% CI 1.32–4.18) (John Hopkins Study Team 1989). Left untreated, it has also been associated with increased low birth weight and infant mortality (Ryan et al 1990).

Babies born to mothers who have cultured positive to C. trachomatis, may subsequently also culture positive (approximately 25%) and have been reported to have higher rates of neonatal conjunctivitis, lower respiratory tract infections and pneumonia (Schachter et al 1986; Preece et al 1989).

However, the NICE guidelines note that the causal link between chlamydia infection and adverse outcomes of pregnancy has not been established and the evidence remains difficult to evaluate in relation to neonatal morbidities (NICE 2008).

40.2 Chlamydia testing in pregnancy

The NICE guidelines reviewed the evidence on diagnostic accuracy and effectiveness of testing methods in identifying genital chlamydia and found no good evidence to support routine antenatal testing.

40.2.1 Diagnostic accuracy

The evidence on diagnostic accuracy was limited to prospective cohort studies. The accuracy of antigen detection tests using endocervical specimens (Stamm et al 1984; Baselski et al 1987; Smith et al 1987) and of nucleic acid amplification tests using first-void urine and endocervical specimens (Thejls et al 1994; Andrews et al 1997; Garland et al 2000; Macmillan et al 2003; Renton 2006) was supported. While nucleic acid hybridisation test (DNA probe test) may be accurate, the evidence is limited and of moderate quality (Yang et al 1991; Hosein et al 1992). Based on limited evidence, Gram staining (Asbill et al 2000) and Pap smear (Spence et al 1986) had insufficient accuracy to detect chlamydia.

40.2.2 Effectiveness of testing

Review of the effectiveness of testing in reducing adverse outcomes for the pregnancy and the neonate found limited evidence (one RCT [(Martin et al 1997)] and five cohort studies [(Macmillan et al 1985; Black-Payne et al 1990; Cohen et al 1990; Ryan et al 1990; Rivlin et al 1997)]) to indicate that treating chlamydia infection during pregnancy is effective in reducing the incidence of premature rupture of the membranes, preterm birth and low birth weight babies. There was no significant evidence to show that treating chlamydia infection during pregnancy leads to decreased incidence of adverse neonatal outcomes (conjunctivitis, pneumonia).

The literature review conducted to inform these Guidelines found no additional systematic reviews or RCTs to support or refute the findings presented in the NICE guidelines. However, there is additional information from systematic reviews and prevalence studies from 2008–2010 to suggest a specific population-based testing program (eg for those at highest risk). This evidence is discussed below.

40.2.3 Groups at higher risk

Antenatal care provides an opportunity to discuss chlamydia testing with young women. Other considerations before testing is offered include whether the pregnancy is unplanned, the number of recent male sexual partners and antibiotic use in the previous 3 months (Chen et al 2009).

In the United Kingdom and the United States, chlamydia testing is recommended for pregnant women younger than 25 years (NICE 2008) and younger than 24 years (The Kirby Institute 2017b), respectively. Testing of young women in Australia is supported by:

  • the high prevalence of chlamydia in young people in Australia (Vajdic et al 2005; NCHECR 2009) and modelling that predicts a reduction in prevalence through testing of people aged 25 years or younger (Regan et al 2008)
  • estimates of the prevalence of chlamydia during pregnancy in young Australian women, which range from 3.2% (95% CI 1.8 to 5.9) among women aged 16–24 (n=403) (Chen et al 2009) to 13.7% among women aged 20 years or younger (n=212) (Cheney & Wray 2008)
  • qualitative research conducted as part of a prospective, cross-sectional study of pregnant women aged 16–25 years, which found a high level of acceptability of testing (Bilardi et al 2010).


  • Grade C
  • 46

Do not routinely offer chlamydia testing to all women as part of antenatal care. 

Approved by NHMRC in December 2011; expire December 2016 UNDER REVIEW


  • Grade C
  • 47

Routinely offer chlamydia testing at the first antenatal visit to pregnant women younger than 25 years. 

Approved by NHMRC in December 2011; expire December 2016 UNDER REVIEW

While data are lacking to support routine testing, the prevalence of chlamydia is regionally variable and, in some areas, high prevalence may occur with that of other sexually transmitted infections, such as gonorrhoea. While testing of young women should take place in all areas, it is also important for health professionals to be aware of the rates of sexually transmitted infection in their community and develop local protocols accordingly.


  • Practice point
  • BBB

Testing for chlamydia and other sexually transmitted infections regardless of age should be considered for women who live in areas where their prevalence is high. An understanding of local prevalence will inform planning for population testing when this is indicated.

Approved by NHMRC in December 2011; expire December 2016 UNDER REVIEW

40.2.4 Type and timing of test

As discussed above, antigen detection (eg nucleic acid amplification tests) are accurate in diagnosing chlamydia. Study of the acceptability of these tests to young woman found a preference for non-invasive methods. Both urine and vulval swab methods were highly sensitive, acceptable, and not affected by pregnancy status (Macmillan et al 2003). However, women may be unable to produce urine on demand and unrefrigerated transport time has been reported to influence sensitivity of testing. There is also preliminary evidence that urine has the lowest organism load when compared to endocervical, self-collected vaginal, and urethral specimens.

40.3 Practice summary: chlamydia


At the first contact with women younger than 25 and women in high prevalence areas.


  • Midwife
  • GP
  • obstetrician
  • Aboriginal and Torres Strait Islander health worker
  • multicultural health worker.


  • Discuss chlamydia
    Explain the association between chlamydia and preterm birth and low birth weight, that tests for the infection are available and that it is easily treated with antibiotics.
  • Take a holistic approach
    If a woman tests positive for chlamydia, other considerations include counselling, contact tracing, partner testing, testing for other sexually transmitted infections and follow-up.
  • Learn about locally available resources
    Available testing services and support organisations will vary by location.

40.4 Resources


  • Andrews WW, Lee HH, Roden WJ et al (1997) Detection of genitourinary tract Chlamydia trachomatis infection in pregnant women by ligase chain reaction assay. Obstet Gynecol 89(4): 556–60.
  • Asbill KK, Higgins RV, Bahrani-Mostafavi Z et al (2000) Detection of Neisseria gonorrhoeae and Chlamydia trachomatis colonization of the gravid cervix including commentary by Mammel JB with author response. Am J Obstet Gynecol 183(2): 340–46.
  • Baselski VS, McNeeley SG, Ryan (1987) A comparison of nonculture-dependent methods for detection of Chlamydia trachomatis infections in pregnant women. Obst Gynecol 70(1): 47–52.
  • Bilardi JE, De Guingand DL, Temple-Smith MJ et al (2010) Young pregnant women’s views on the acceptability of screening for chlamydia as part of routine antenatal care. BMC Public Health 10: 505.
  • Black-Payne C, Ahrabi MM, Bocchini JA Jr et al (1990) Treatment of Chlamydia trachomatis identified with Chlamydiazyme during pregnancy. Impact on perinatal complications and infants. J Reproductive Med 35(4): 362–67.
  • Chen MY, Fairley CK, De Guingand D et al (2009) Screening pregnant women for chlamydia: what are the predictors of infection? Sex Transm Infect 85: 31–35.
  • Cheney K & Wray L (2008) Chlamydia and associated factors in an under 20s antenatal population’, Aust NZ J Obstet Gynaecol 48(1): 40–43.
  • Cohen I, Veille J-C, Calkins BM (1990) Improved pregnancy outcome following successful treatment of chlamydial infection. JAMA 263: 3160–63.
  • Garland SM, Tabrizi S, Hallo J et al (2000) Assessment of Chlamydia trachomatis prevalence by PCR and LCR in women presenting for termination of pregnancy. Sex Transm Infect 76(3): 173–76.
  • Geisler WM, Wang C, Morrison SG et al (2008) The natural history of untreated Chlamydia trachomatis infection in the interval between screening and returning for treatment. Sex Transm Dis 35(2): 119–23.
  • Hosein IK, Kaunitz AM, Craft SJ (1992) Detection of cervical Chlamydia trachomatis and Neisseria gonorrhoeae with deoxyribonucleic acid probe assays in obstetric patients. Am J Obstet Gynecol 167(3): 588–91.
  • John Hopkins Study Team (1989) Association of chlamydia trachomatis and mycoplasma hominis with intrauterine growth restriction and preterm delivery. The John Hopkins Study of Cervicitis and Adverse Pregnancy Outcome. Am J Epidemiol 129: 1247–51.
  • Macmillan JA, Weiner LB, Lamberson HV et al (1985) Efficacy of maternal screening and therapy in the prevention of chlamydia infection of the newborn. Infection 13(6): 263–66.
  • Macmillan S, McKenzie H, Templeton A (2003) Parallel observation of four methods for screening women under 25 years of age for genital infection with Chlamydia trachomatis. Eur J Obstet Gynecol Reprod Biol 107(1): 68–73.
  • Martin DH, Eschenbach DA, Cotch MF et al (1997) Double-blind placebo-controlled treatment trial of chlamydia trachomatis endocervical infections in pregnant women. Infect Dis Obstet Gynecol 5(1): 10–17.
  • NICE (2008) Antenatal Care. Routine Care for the Healthy Pregnant Woman. National Collaborating Centre for Women’s and Children’s Health. Commissioned by the National Institute for Health and Clinical Excellence. London: RCOG Press.
  • Preece PM, Anderson JM, Thompson RG (1989) Chlamydia trachomatis infection in infants: A prospective study. Arch Dis Childhood 64: 525–29.
  • Regan DG, Wilson DP, Hocking JS et al (2008) Coverage is the key for effective screening of Chlamydia trachomatis in Australia. J Infect Dis 198(3): 349–58.
  • Renton A (2006) Chlamydia trachomatis in cervical and vaginal swabs and urine specimens from women undergoing termination of pregnancy. Int J STD AIDS 17(7): 443–47.
  • Rivlin ME, Morrison JC, Grossman JH (1997) Comparison of pregnancy outcome between treated and untreated women with chlamydial cervicitis. J Mississippi State Med Assoc 38(11): 404–07.
  • Rogers SM, Miller WC, Turner CF et al (2008) Concordance of chlamydia trachomatis infections within sexual partnerships. Sex Transm Infect 84(1): 23–28.
  • Ryan GM, Jr, Abdella TN, McNeeley SG et al (1990) Chlamydia trachomatis infection in pregnancy and effect of treatment on outcome. Am J Obstet Gynecol 162: 34–39.
  • Schachter J, Grossman M, Sweet RL et al (1986) Prospective study of perinatal transmission of Chlamydia trachomatis. JAMA 255: 3374–77.
  • Smith JW, Rogers RE, Katz BP et al (1987) Diagnosis of chlamydial infection in women attending antenatal and gynecologic clinics. J Clin Microbiol 25(5): 868–72.
  • Spence MR (1986) A correlative study of Papanicolaou smear, fluorescent antibody, and culture for the diagnosis of Chlamydia trachomatis. Obstet Gynecol 68(5): 691–95.
  • Stamm WE, Harrison HR, Alexander ER et al (1984) Diagnosis of Chlamydia trachomatis infections by direct immunofluorescence staining of genital secretions. A multicenter trial. Annals Int Med 101(5): 638–41.
  • Thejls H, Gnarpe J, Gnarpe H et al (1994) Expanded gold standard in the diagnosis of Chlamydia trachomatis in a low prevalence population: diagnostic efficacy of tissue culture, direct immunofluorescence, enzyme immunoassay, PCR and serology. Genitourin Med 70(5): 300–03.
  • The Kirby Institute (2017a) Bloodborne viral and sexually transmissible infections in Aboriginal and Torres Strait Islander people: Annual surveillance report 2017. Sydney: The Kirby Institute, UNSW Australia.
  • The Kirby Institute (2017b) HIV, viral hepatitis and sexually transmissible infections in Australia. Annual Surveillance Report 2017. Sydney: The Kirby Institute, UNSW.USPSTF (2007) Screening for Chlamydial Infection: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med 147: 128–34.
  • Vajdic CM, Middleton M, Bowden FJ et al (2005) The prevalence of genital Chlamydia trachomatis in Australia 1997–2004: a systematic review. Sex Health 2 (3): 169–83.
  • Yang LI, Panke ES, Leist PA et al (1991) Detection of Chlamydia trachomatis endocervical infection in asymptomatic and symptomatic women: comparison of deoxyribonucleic acid probe test with tissue culture. Am J Obstet Gynecol 165(5 Pt1): 1444–53.
Last updated: 
20 November 2018