Intrauterine growth retardation (IUGR) is a phenomenon that occurs in mammalian foetuses due to a reduced placental transfer of nutrients from the mother, most often associated with chronic stress exposure in sows during the second and third trimester of pregnancy. The aim of the present study was to investigate the frequency of IUGR in relation to parity and seasonal variation in climate parameters, including temperature, humidity, and light conditions in the gestation area. The study was conducted on a production farm with strict biosecurity and animal health management. Pig neonates were identified as IUGR based on established criteria, including birth body weight and head morphology. The frequency of IUGR pigs in a litter increased with parity, from null in primiparous sows to 13.3% in multiparous sows (>7 gestations). The lowest frequency of IUGR neonates (stillborn and live-born) was observed in summer, whereas the highest proportion was recorded in autumn. In conclusion, significant differences in the frequency of stillbirths and live births of piglets with IUGR were demonstrated at different times of the year, and it was hypothesised that reduced daylight duration could contribute to this effect.