Hair cortisol levels in pregnancy as a possible determinant of fetal sex: a longitudinal study Romero González, Borja Puertas González, José Antonio González Pérez, Raquel Davila, Marta Peralta Ramírez, María Isabel Cortisol Pregnancy Stress Fetus Sex Stress during pregnancy has been widely studied and associated to different variables, usually with negative results for the health of the mother and the newborn, such as having a higher risk of suffering postpartum depression, premature birth, obstetrics complications or low birthweight, among others. However, there are not many lines of research that study the role that the sex of the baby plays on this specific stress and vice versa. Thus, the main objective was to analyse the relationship between the sex of the offspring and the stress of the mothers in the first trimester of pregnancy. In order to achieve this, 108 women had their biological stress measured (trough hair cortisol levels) and psychological stress evaluated (the Prenatal Distress Questionnaire (PSS), the Perceived Stress Scale (PDQ) and the Stress Vulnerability Inventory (IVE)). The results revealed significant differences in maternal hair cortisol levels in the first trimester based on the sex of the baby they had given birth to (t = −2.04; P < 0.05): the concentration of the hormone was higher if the baby was a girl (164.36: 54.45-284.87 pg/mg) than if it was a boy (101.13:37.95-193.56 pg/mg). These findings show that the sex of the future baby could be conditioned, among many other variables, by the mother´s stress levels during conception and first weeks of pregnancy. Further research is needed in this area to support our findings. 2021-03-02T08:03:56Z 2021-03-02T08:03:56Z 2020 info:eu-repo/semantics/article Romero-Gonzalez, B., Puertas-Gonzalez, J., Gonzalez-Perez, R., Davila, M., & Peralta-Ramirez, M. (2021). Hair cortisol levels in pregnancy as a possible determinant of fetal sex: A longitudinal study. Journal of Developmental Origins of Health and Disease, 1-6. doi:10.1017/S2040174420001300 http://hdl.handle.net/10481/66758 10.1017/S2040174420001300 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Cambridge University Press