Background: Sexually transmitted infections (STIs) pose major risks in pregnancy, including stillbirth, preterm delivery, and congenital infections. Globally, pooled antenatal prevalence estimates are HIV 2.9%, HBV 4.8%, HCV 1.0%, and syphilis 0.8%, but burdens are higher in low-income countries, reaching HIV 5.2%, HBV 6.6%, HCV 2.7%, and syphilis 3.3% ( ). In Ghana, reported rates are variable: HBV 4-10%, HCV 0.8-12%, HIV 1-3%, and syphilis 0.4-3.6%. Despite a national policy mandating integrated antenatal screening, evidence on the prevalence and co-infection patterns among pregnant women remains fragmented. This study aimed to determine the prevalence of HIV, HBV, HCV, and syphilis, co-infections, and associated determinants among Ghanaian pregnant women. Methods: A cross-sectional study was conducted using secondary data from 1,316 pregnant women attending antenatal care across four municipalities in Ghana (2023-2024). Prevalence, co-infection patterns, and risk factors were assessed using descriptive statistics, logistic regression, and kappa agreement tests. Results: The median age of participants was 28 years (IQR: 23-33). Syphilis was most prevalent (10.5%), followed by HBV (4.0%), HIV (2.5%), and HCV (1.9%). Marked geographic disparities were observed, with syphilis prevalence ranging from 0.8% in Afigya Kwabre to 38.9% in Cape Coast. Co-infections were common: 26.6% of HBV-positive women also had syphilis ({kappa} = 0.348, p < 0.001), and 16.6% of HIV-positive women had syphilis ({kappa} = 0.237, p < 0.001). Predictors of syphilis included urban residence (aOR: 4.79; 95% CI: 2.99-7.69), multiparity (aOR: 3.08; 95% CI: 1.92-4.96), and early gestational age. Conclusion: The high burden of syphilis and frequent co-infections among Ghanaian pregnant women reveal critical gaps in implementing integrated antenatal screening. Despite national policy mandates, inconsistent practice leaves mothers and infants vulnerable to preventable complications. Strengthening compliance with comprehensive STI screening while tailoring interventions to high-risk groups is essential to reducing adverse maternal and neonatal outcomes.