Trends of sexually transmitted infections among pregnant women in Melbourne, Australia, 2012–2025: a rise in burden of syphilis

BACKGROUND: Sexually transmitted infections in pregnancy threaten both mother and baby, so early detection matters. This study aimed to describe the epidemiology and temporal trends of sexually transmitted infections (STIs) among pregnant women attending a large public sexual health clinic in Melbourne, Australia, from 2012 to 2025. METHODS: We retrospectively analysed electronic medical records from the Melbourne Sexual Health Centre, a large public sexual health service. Demographic, clinical, and laboratory data were extracted for pregnant women who attended in 2012-2025, including those referred by primary care providers. STI positivity were calculated with 95% confidence intervals (CI), and temporal trends were assessed using trend tests. RESULTS: Of 659 pregnant women, 111 (16.8%, 95% CI: 14.2-19.9%) had one or more STIs. Positivity was 12.2% (46/377) for syphilis, 10.9% (57/523) for chlamydia, 2.1% (9/385) for gonorrhoea, 0.6% (2/335) for HIV, and 2.3% (5/218) for trichomoniasis. Of syphilis cases, 73.9% were diagnosed in the first trimester. Syphilis positivity increased over the study period (Ptrend = 0.022), peaking in 2022-2023 (35.0%, 7/20), while other STIs remained stable. CONCLUSIONS: STIs were frequently detected among pregnant clinic attendees, with syphilis and chlamydia the most prevalent. The rising burden of syphilis highlights the need for strengthened antenatal testing and timely public health responses.