Objective: To identify determinants which influence the timing of the first antenatal care (ANC) visit in pregnant women. Design: Retrospective matched nested case-control study. Setting: Two health centres, Belén and 6 de Octubre, in the Peruvian Amazon. Population: All pregnant women who had attended ANC during the years 2010, 2011, and 2012. Methods: All cases (819 women initiating ANC in their first trimester) were selected from ANC registries from 2010 to 2012. A random sample of controls (819 women initiating ANC in their second or third trimester) was matched 1:1 to cases on health centre and date of first ANC visit. Data were obtained from ANC registries. Conditional logistic regression analyses were performed. Main outcome measure: Case-control status of each woman determined by the gestational age at first ANC visit. Results: Cases had higher odds of: 1) being married or cohabiting (aOR = 1.69;95% CI: 1.19, 2.41); 2) completing secondary school or attending post-secondary school (aOR = 1.45;95% CI: 1.02, 2.06); 3) living in an urban environment (aOR = 1.79;95% CI: 1.04, 3.10) and 4) having had a previous miscarriage (aOR = 1.56;95% CI: 1.13, 2.15), compared to controls. No statistically significant difference in odds was found for parity (aOR = 1.08;95% CI: 0.85, 1.36). Conclusions: This study provides empirical evidence of determinants of first ANC attendance. These findings are crucial to the planning and timing of local interventions, like deworming, aimed at pregnant women so that they can access and benefit fully from all government-provided ANC services.