Sexually transmitted infections (STIs) are particularly important to manage in pregnancy, and their incidence is closely linked to socioeconomic determinants such as poverty, poor access to healthcare, incarceration, and intergenerational trauma.¹ STIs remain a preventable driver of adverse pregnancy outcomes in Australia. Beyond causing cervicitis and ascending infection, STIs can affect pregnancy through varied, pathogen-specific pathways. This article provides a clinical overview of three common STIs – chlamydia, gonorrhoea, and bacterial vaginosis – focusing on their prevalence, associated pregnancy and neonatal complications, presentation, risk groups, and the current antenatal screening and treatment guidelines within Australia.

Chlamydia

Chlamydia (chlamydia trachomatis) remains the most frequently notifiable STI in Australia, with over 109,451 new cases reported in 2023 alone. It affects both genders equally and is prevalent among people aged 15–29 years.² Rates are disproportionately higher among Aboriginal and Torres Strait Islander peoples, particularly in remote communities, where prevalence is twice that of non-Indigenous populations.¹ These disparities reflect broader socioeconomic inequities, including reduced access to culturally safe healthcare, systemic disadvantage, and impacts of colonisation and intergenerational trauma.

Pregnancy risk: Chlamydia can ascend from the lower genital tract into the uterus, provoking an inflammatory cascade, associated with increased risk of preterm birth, low birth weight, and perinatal mortality.^3,4 A large Australian study demonstrated a link between maternal chlamydia and small for gestation age (SGA) infants.⁴ Chlamydia in pregnancy is associated with neonatal complications including conjunctivitis and pneumonia.⁵

Presentation: It is estimated that 85-90% of infections are silent. Asymptomatic infections persist unless actively screened for, contributing substantially to population disease burden. Symptomatic infection is uncommon but may present with dysuria, vaginal discharge, pelvic pain, and/or anorectal symptoms, depending on infection site. Complications include ectopic pregnancy, pelvic inflammatory disease (PID), and infertility.⁶

Screening: Most Australian guidelines, including RANZCOG’s, support a risk-based screening approach, recommending testing at the first antenatal visit to pregnant women <30 years and those at increased risk (i.e. new or multiple partners, prior STI diagnosis, residing in high prevalence regions).⁷ In rural Western and Northern Australia, third trimester testing is already routine antenatal practice.⁸ Despite this, research highlights screening gaps, particularly among Aboriginal and Torres Strait Islander women, who experience higher rates of chlamydia-related adverse pregnancy outcomes. Strengthening culturally appropriate and accessible antenatal screening remains a public health priority to reduce the burden of chlamydia in pregnancy across Australia.^1,4

Treatment: First line treatment for vaginal chlamydia in pregnancy is stat oral azithromycin 1g. The use of tetracyclines in pregnancy is contraindicated due to the risk of tooth discolouration and impaired bone development in the foetus.⁵ Education, partner notification and treatment, and contact tracing of all sexual partners in the last six months is critical to prevent maternal reinfection, hence improving maternal-neonatal outcomes. Test of cure (TOC) is recommended four weeks after treatment to avoid false positives from residual DNA, with retesting at three months to detect reinfection.⁶

Gonorrhoea

Australia recorded 44,210 gonorrhoea (Neisseria gonorrhoeae) notifications in 2024, representing an increase of 211% over the last decade. Of those new notifications, 11,989 were reported in women, and people aged 15-29 years made up 45% of total notifications.⁹ Among Aboriginal and Torres Strait Islander peoples, the 2023 age-standardised notification rate was more than four times the non-Indigenous rate.²

Pregnancy risk: In pregnancy, gonorrhoea is associated with adverse outcomes including ectopic pregnancy, preterm birth, SGA, low birth weight, and a twofold rise in stillbirth rates.^4,10 Vertical transmission during pregnancy is between 30 to 47%.¹⁰ This can lead to neonatal complications including ophthalmia neonatorum, meningitis, sepsis, and rarely, disseminated gonococcal infection.¹¹

Presentation: As 80% of vaginal gonorrhoea is asymptomatic, active screening is needed to detect infection.¹² Serious complications include ectopic pregnancy, PID, infertility, and severe neonatal eye infections that may lead to blindness. Gonorrhoea is also associated with a five-fold increased risk of HIV transmission.¹⁵

Screening: Screening is recommended for pregnant women <30 years, with known risk factors, or those living in rural/remote areas.¹⁰

Treatment: Treatment with intramuscular ceftriaxone 500mg (with 1% lidocaine) plus azithromycin (1g) is first line treatment in pregnancy for vaginal gonorrhoea.¹⁰ Multi-drug resistant gonorrhoea is rising worldwide, highlighting the importance of pre-treatment swabs for culture and susceptibilities, and post-treatment test of cure at two weeks to identify resistant strains, detect treatment failures, and provide alternative treatment.¹²

Bacterial Vaginosis

Bacterial vaginosis (BV) is a polymicrobial vaginal dysbiosis with lactobacilli depletion that affects almost a third of reproductive-aged women globally. It presents with malodorous vaginal discharge and is associated with high recurrence rates.¹³

Pregnancy risk: BV in pregnancy is associated with preterm birth, low birth weight, and postpartum endometritis.¹³ BV in pregnancy is more prevalent among women of lower socioeconomic status and/or history of preterm birth. A Cochrane review found whilst antibiotic therapy is effective in eradicating bacterial vaginosis in pregnancy, there was no evidence that treatment of antenatal women with BV resulted in reduced preterm births. Evidence that routine screening in asymptomatic women improves outcomes are limited.¹⁴ Emerging evidence suggests that early treatment before 20 weeks of pregnancy may be beneficial for women with a history of preterm birth.¹⁴

Screening: Current Australian guidelines do not recommend screening in asymptomatic pregnant women with low-risk pregnancies.

Treatment: Treatment of choice is with oral metronidazole 400mg BD with food for seven days, or intravaginal therapy with metronidazole 0.75% gel or clindamycin 2% cream. A recent Australian study found reinfection is a significant driver for recurrence, and that BV is sexually transmissible. Concomitant partner treatment should be offered to regular male partners of women with BV.¹³

Conclusion

Addressing the burden of sexually transmitted infections (STIs) in pregnancy requires a proactive, risk-based approach to antenatal care. Universal screening for chlamydia and gonorrhoea, and interval screening in high-prevalence populations can help detect asymptomatic infections early in pregnancy, reducing maternal and neonatal complications.

Timely treatment using the pregnancy and risk-specific sections in the Australian STI Management Guidelines is essential. Routine test-of-cure and third trimester retesting for those at ongoing high risk, alongside prompt partner management and contact tracing, are critical to preventing reinfection and improving outcomes.¹⁶

Embedding equitable care models using robust recall systems, standardised partner management pathways, and culturally safe models of service delivery including self-collection and telehealth, ensures all at-risk women can access care safely. These strategies collectively strengthen antenatal STI management and contribute to reducing preventable adverse pregnancy outcomes across Australia.