BackgroundSao Tome & Principe (STP) has a high peri-neonatal mortality rate and access to high-quality care before childbirth has been described as one of the most effective means of reducing it. The country has a gap in the coverage-content of antenatal care (ANC) services that must be addressed to better allocate resources to ultimately improve maternal and neonatal health. Therefore, this study aimed to identify the determinants for adequate ANC utilization considering the number and timing of ANC contacts and screening completion.MethodsA hospital based cross-sectional study was undertaken among women admitted for delivery at Hospital Dr. Ayres de Menezes (HAM). Data were abstracted from ANC pregnancy cards and from a structured face-to-face interviewer-administered questionnaire. ANC utilization was classified as partial vs adequate. Adequate ANC utilization was defined as having ANC 4 or more contacts, first trimester enrolment plus one or more hemoglobin tests, urine, and ultrasound. The collected data were entered into QuickTapSurvey and exported to SPSS version 25 for analysis. Multivariable logistic regression was used to identify determinants of adequate ANC utilization atP-value < 0.05.ResultsA total of 445 mothers were included with a mean age of 26.6 ± 7.1, an adequate ANC utilization was identified in 213 (47.9%; 95% CI: 43.3–52.5) and a partial ANC utilization in 232 (52.1%; 95% CI: 47.5–56.7). Age 20–34 [AOR 2.27 (95% CI: 1.28–4.04),p= 0.005] and age above 35 [AOR 2.5 (95% CI: 1.21–5.20),p= 0.013] when comparing with women aged 14–19 years, urban residence [AOR 1.98 (95% CI: 1.28–3.06),p< 0.002], and planned pregnancy [AOR 2.67 (95% CI: 1.6–4.2),p< 0.001] were the determinants of adequate ANC utilization.ConclusionLess than half of the pregnant women had adequate ANC utilization. Maternal age, residence and type of pregnancy planning were the determinants for adequate ANC utilization. Stakeholders should focus on raising awareness of the importance of ANC screening and engaging more vulnerable women in earlier utilization of family planning services and choosing a pregnancy plan, as a key strategy to improve neonatal health outcomes in STP.