Estradiol (E), testosterone (T), and their ratio are crucial axis in life. Especially during intrauterine growth, they orchestrate the complex development of organs and their interaction, which have lifelong impact on health and an organism's capacity to respond to environmental stressors. The aim of this study was to compare for the first time E, T, and their ratio levels with aromatase (CYP19) gene methylation levels between preterm newborns (PN) and full-term newborns (FN) with respect to their mother's environmental exposure and diet. In this study, 56 FN of 37-42 weeks of gestation age (GA) and 46 PN at GA 27-36 weeks were analysed for E and T levels and CYP19A1 gene pI.3/II promoter region methylation. Results showed there was no difference in E levels between PN and FN, but there were significantly lower levels of T in PN than in FN (2.81 nmol vs. 3.76 nmol, respectively) and consequently a significantly higher E/T ratio in PN than in FN (5278.04 vs. 2891.23, respectively). CYP19A1 methylation was significantly lower in PN than in FN (86.04% vs. 90.04%, respectively). CYP19A1 methylation was significantly reduced in newborns whose mothers reported daily milk consumption. Our study is the first to provide referent values for CYP19A1 methylation levels in FN and PN and shows that PN and FN significantly differ in CYP19A1 methylation levels, T levels, and E/T ratio. Future research should further investigate the mechanisms involved in GA-dependent CYP19A1 methylation levels and mechanisms of sex hormone disturbances which may contribute to preterm birth.