Objective: The present study aimed to evaluate the association between syphilis in pregnancy and low birth weight, small for gestational age, and preterm birth. Methods: This longitudinal study used Brazilian National Information System for livebirths (SINASC) linked to the gestational syphilis cases from Notifiable Diseases Information System (SINAN) from 2011 to 2017. Descriptive statistics and logistic regression were used to compare the birth outcomes of pregnant women with and without syphilis. The study protocol was approved by the Research Ethics Committee of the Institute of Collective Health of the Federal University of Bahia (CAAE: registration no. 18022319.4.0000.5030). Results: A total of 17 930 817 live births were included in the study. Of these, 155 214 (8.7/1000) were exposed to syphilis during pregnancy. Maternal syphilis increased the odds of low birth weight (aOR 1.88, 95% CI: 1.85-1.91), small for gestational age (aOR 1.53, 95% CI: 1.51-1.56), and preterm birth (aOR 1.35, 95% CI: 1.33-1.37). Higher odds were observed for pregnant women with VDRL titer ≥64 and untreated maternal syphilis when compared to mothers without syphilis. Analysis stratified by prenatal care showed higher odds for all adverse birth outcomes for mothers attending ≤6 prenatal appointments. Conclusion: Our findings showed a strong association between gestational syphilis and adverse birth outcomes with increased odds observed among women with higher VDRL titers, lack of treatment, and fewer prenatal appointments. These results highlight the need for adequate screening and treatment for gestational syphilis during pregnancy to mitigate the risk of adverse birth outcomes.