Background <p>Iron-folic acid supplementation is one of the key interventions provided during antenatal care (ANC) services to reduce iron deficiency, maternal anemia, low birthweight and other pregnancy-related complications responsible for maternal and neonatal mortality. However, use of iron-folic acid supplements and adherence with recommended dosage in Nigeria is low. The purpose of this cross-sectional study was to examine factors associated with iron-folic acid supplements use among pregnant women in Karu local government area (LGA), Nasarawa, Nigeria.</p> Methods <p>Questionnaires were administered in face-to-face interviews with 64 pregnant women (aged 18–49 years) and 19 healthcare providers in selected public primary health facilities across Karu LGA, Nasarawa State. Using the theory of planned behavior, pregnant women’s intention to use iron-folic acid supplements during pregnancy was predicted. In addition, factors associated with adherence to duration of use were also examined. Multiple linear regression was performed to examine the effect of attitudes, subjective norms and perceived behavioral control on intention to use, and binary logistic regression was used to examine factors associated with adherence to duration of use. Data was analyzed using STATA 15.0.</p> Results <p>Almost all participants (97%) reported using iron-folic acid supplements, and 54% reported using iron-folic acid supplements daily. Subjective norm (<i>p</i> &lt; 0.05) and perceived behavioral control (<i>p</i> &lt; 0.05) significantly predicted intention to use iron-folic acid supplements during pregnancy. However, attitude did not have a predictive influence on intention. Also, pregnant women made an average of 2.7 antenatal care visits (standard deviation (SD) = 1.6), with most women (59%) having their first antenatal care visit within the second trimester (4–6 months) of pregnancy. Only one out of five attended within the first trimester (1–3 months). Overall, for every additional antenatal care visit, there was a significant increase in the likelihood of taking iron-folic acid supplements for three months or more (<i>p</i> &lt; 0.05).</p> Conclusions <p>This study showed that perceived behavioral control and subjective norm were predictors of intention to use iron-folic acid supplements. Frequency of antenatal care visits was significantly associated with adherence to duration of iron-folic acid supplement use. Antenatal care attendance is very critical to the use of iron-folic acid supplements and should be promoted.</p>