This study investigates the impact of both maternal psychopathological factors and adaptive psychological changes within the couple on fetal growth, emphasizing the importance of evaluating pregnancy from the perspectives of the couple, the mother, and the fetus collectively. A "couple" in this context refers to heterosexual partners engaged in the pregnancy process together, whether married or in a stable relationship. We included 189 pregnant women in their first trimester, tracking maternal depression, anxiety, body appreciation, prenatal attachment, and the couple's adjustment level across each trimester. Fetal growth parameters measured include biparietal diameter, femur length, humerus length, abdomen circumference, head circumference, β-HCG, and amniotic fluid levels, with relationships between these variables being modeled accordingly. Our findings indicate stable levels of maternal depression, anxiety, body appreciation, and couple's adjustment throughout the pregnancy, with a significant increase in prenatal attachment levels in each subsequent trimester. Prenatal attachment in the first trimester and maternal depression levels in the second and third trimesters were found to directly influence fetal growth, while other variables exhibited indirect effects. Fetal growth is influenced by a myriad of biopsychosocial factors. Ensuring healthy pregnancy and fetal development necessitates close monitoring and support of the mother's adaptive psychological changes, early identification and treatment of potential psychopathologies, and maintenance of the psychosocial health of the couple.