BACKGROUND: Maternal stress and psychopathology have a negative effect on mothers and neonates. Maternal stress may affect neonatal growth and development both physically and psychologically. PURPOSE: To study the impact of pandemic-related pregnancy stress and maternal psychopathological symptoms during the COVID-19 lockdown in 2020 on neonatal development. METHODS: A two-phase prospective study was carried out on a sample of 181 pregnant women ranged from 18 to 40 years old in Spain (Europe). Phase 1: Pandemic-related pregnancy stress (PREPS), Prenatal Distress Questionnaire (PDQ), Perceived Stress Scale (PSS) and the revised version of the Symptom Checklist-90 (SCL-90-R) were used to assess psychological symptoms during the lockdown. In the follow-up (Phase 2), obstetric, birth-related and anthropometric variables were collected from 81 pregnant women-neonates dyads. RESULTS: Primiparous women showed higher psychopathological symptoms and higher levels of pandemic-related pregnancy stress than multiparous women. A multiple linear regression model showed that pandemic-related pregnancy stress could predict the length of neonate by adjusting for maternal age and gestational age, especially for primiparous women. IMPLICATIONS FOR RESEARCH: Studies assessing neonates development should evaluate the long-term effect of the COVID-19 pandemic on neonates´ length. IMPLICATIONS FOR PRACTICE: States the relation between pandemic-related pregnancy stress and neonatal development by being able to track the effects on neonates whose mothers had high levels of stress during the COVID-19 pandemic.