In the fetal placenta side of women diagnosed with GDM and control pregnancies, it was observed that in the experimental group, the DNA methylation of the serotonin transporter gene SLC6A4 (solute carrier family 6 member 4) was increased in the controls, indicating that the in utero environment can alter the serotonin system due to this neurotransmitter being involved in growth and neurodevelopment in utero. The gene discussed is SLC6A4; the disease is gestational diabetes.