A 30-year Polish cohort study covering the COVID-19 pandemic period indicates shifts in the age of infants’ motor development milestones

Abstract Infants’ motor development is influenced by genetic and environmental factors. The objective of this study is to investigate whether there are differences in the age of gross motor skill development between cohorts observed over a 30-year period, and if these differences are observed among children born during the COVID-19 pandemic. The analysis included 1348 children (613 girls and 735 boys).The data comes from three cohorts. The first cohort consists of children born in the years 1992–1997, the second born in the years 2003–2008, and the third of children born just before and during the COVID-19 pandemic, in the years 2019–2022. In each cohort, parents were invited to complete a survey questionnaire concerning the gross motor development of their children. Furthermore, the respondents were asked about the type of infant feeding in the first months of life (breastfeeding versus formula feeding) and the parents’ educational level. Multiple regression analysis was used to identify the factors influencing the age at which gross motor development milestones are reached. The Kruskal-Wallis test showed significant differences in the age at which children began independent sitting (H = 168.91, p < 0.001), independent standing (H = 91.83, p < 0.001) and independent walking (H = 66.94, p < 0.001) between children born in the three cohorts. The multiple regression model showed that the factors negatively correlated with the age at which children can sit independently are the cohorts 1992–1997 and 2003–2008 compared with the cohort 2019–2022 (Beta = -0.372; p < 0.001 and Beta = -0.236; p < 0.001, respectively), formula feeding compared with breastfeeding (Beta = 0.054; p = 0.049) and the mother’s secondary education level compared with higher education (Beta = -0.085; p = 0.021). Furthermore, factors negatively correlated with the age of independent standing are cohorts from 1992 to 1997 and 2003–2008 vs. 2019–2022 (respectively Beta = -0.268; p < 0.001 and Beta = -0.166; p < 0.001). The same factors are negatively correlated with the age of independent walking – years 1992–1997 vs. 2019–2022 (Beta = -0.280; p < 0.001) and years 2003–2008 vs. 2019–2022 (Beta = -0.189; p < 0.001). In central Poland, in one of the country’s largest cities (Lodz) the shift in the age at which infants reach the stages of gross motor development – significantly later attainment of motor developmental milestones – intensifies with every decade, which may not be without consequences for children’s proper growth and development. For this reason, further research is needed to identify which environmental factors have a significant impact on infants’ gross motor development.