Background: Thyroid dysfunction during pregnancy is associated with adverse maternal and fetal outcomes, including miscarriage, preterm birth and impaired neurodevelopment. Physiological changes in gestation necessitate trimester-specific assessment, yet data from Bangladesh remain limited. Early identification through antenatal screening may reduce preventable complications. This study aimed to determine the trimester-specific distribution of thyroid disorders detected through routine antenatal screening and to assess associated demographic and obstetric factors. Methods: This cross-sectional study was conducted at the Department of Obstetrics and Gynaecology at Bangabandhu Sheikh Mujib Medical University Hospital, Dhaka, from September 2014 to February 2015. Sixty-two pregnant women up to 36 weeks of gestation with singleton pregnancies were enrolled using purposive sampling. Data were collected through structured questionnaires, clinical examination and thyroid function testing. Statistical analysis was performed using SPSS version 17. Results: Nineteen of 62 participants (30.6%) had abnormal thyroid function. Thyroid dysfunction was observed across all trimesters, with a higher proportion detected in the third trimester. Significant associations were found between thyroid dysfunction and maternal age (p = 0.039), menstrual irregularity (p = 0.042), parity (p = 0.025), history of subfertility (p = 0.004) and prior abortion (p < 0.001). Socioeconomic status and gestational age were not significantly associated. Conclusion: A considerable burden of thyroid dysfunction was detected during routine antenatal care. The findings support the implementation of structured thyroid screening strategies during pregnancy to enhance maternal and fetal health outcomes.