The autonomic nervous system (ANS) is involved in cardiovascular, metabolic and cognitive processes, so its study in the fetus can provide relevant functional diagnostic and prognostic information. In particular, the study of the fetal ANS allows us to understand the degree of nervous maturation reached by the fetus and any developmental disorders that could have an impact on the cardiovascular characteristics of the fetus. The goal of this open-label, non-randomized, prospective observational study is to study the fetal ANS in pregnant women between 23 and 40 weeks of gestation. The objetives are: * To Evaluate Fetal Autonomic Nervous System (FANTE) through the analysis of maternal electrocardiogram (ECG) and others clinical parameters usually used in pregnancy monitoring. * To identify any variations in the fetal ECG in the event of developmental or pathological maternal and/or fetal pregnancy. Participants will be recruited during ultrasound visits, information sessions, and hospitalizations after signing informed consent.