Poster #61 - A Quarter-Century of Motor Development: Cohort Effects on Milestone Onsets

• In Event: Poster Session 07

Abstract

Contextual and cultural changes at the societal level can have a cascading effect on motor development. For example, the public health “Back-to-Sleep” Campaign in the 1990’s recommended that parents put infants to bed supine (on their backs) to decrease the risk of Sudden Infant Death Syndrome (SIDS). As a result, supine-sleeping infants started rolling, sitting, crawling, pulling-to-stand, and walking later than prone sleepers (Brouwer et al., 2006; Davis et al., 1998). This study asks whether the average timing of infant motor development changed over 24 years and how societal events and cultural shifts could explain such changes.
Milestone onset data from 566 infants born between 1995 and 2019 was compiled from 36 previously published datasets in which a researcher interviewed parents about their infant’s motor development (blinded for anonymity). Baby books or video recordings assisted parents in pinpointing onset dates for hands-and-knees crawling, cruising, and walking. To examine whether there were general changes in milestone onset ages, we conducted a linear regression analysis for each milestone separately. Next, we used a segmented regression analysis (Muggeo, 2003, 2008) to investigate change in the trajectory of milestone onset age at the group level. We excluded infants with onset ages, birthweight, and gestational age outside of the normal range (CDC, 2010; Berger et al., 2007).
Infants’ crawling onset age did not change significantly over time (Table 1). Infants’ cruising onset age increased 1.00 days per year. Specifically, until 2003 cruising onset age significantly increased by 5.06 days per year (Figure 1). Infants’ walking onset age increased 1.45 days per year. Specifically, the increase in onset age started at the end of 1999.
The lack of change in crawling onset age in this sample, over this time frame, may reflect an earlier change associated with the Back-to-Sleep campaign of the early ‘90’s. In 1996, the American Academy of Pediatrics began to recommend placing infants prone during the day to counteract any motor delays caused by supine sleeping. However, despite knowing that “tummy time” is beneficial for motor development, even today some parents are reluctant to place their infants prone (Palmer et al., 2019). Thus, beneficial effects of tummy time could be lagged and may explain why cruising onset age continued to increase and why it took until 2003 for cruising onset age to plateau. The increase in walking onset age did not plateau and thus seems independent from the prone milestones (Pin et al, 2007). This may be explained by equipment use—after the use of baby walkers decreased from 1994 to 1999 due to safety concerns, parents began using exersaucers to contain their babies. The use of this equipment was associated with motor delays (e.g., Abbott & Bartlett, 2001; DiLillo et al., 2001; Fay et al., 2006; Gee et al., 2020; but see Pin et al., 2007); effects may be ongoing. In conclusion, cohort differences in motor skill acquisition may reflect societal changes related to infant positioning and equipment use. Future analyses will control for possible confounds.

Authors

• Aaron DeMasi, The Graduate Center, The City University of New York
  Presenting Author

• Emiel Schoneveld

• Adrian Tsui

• Sencha Kreymerman

• Sarah E. Berger, City University of New York College of Staten Island