The researchers found that babies who were born in the winter - and who began crawling in the summer - had a quicker pace of motor development than those born in the summer.
According to the American Pregnancy Association, infant development can be divided into four categories: social, language, large motor development and small motor development.
Large motor development involves holding the head up, sitting, pulling up, rolling over, crawling and walking. Though many parents compare their infants with others, the organization cautions that this should be avoided. Instead, parents should relax in knowing that babies develop at different rates and their development should only be compared with their own milestones from the previous week or month.
For this latest study, a team of researchers from the University of Haifa's Department of Physical Therapy and the Department of Counseling and Human Development divided 47 healthy babies with typical development indications into two groups:
- Summer-fall babies: 16 babies born from June-November
- Winter-spring babies: 31 babies born from December-May.
When the babies were 7 months old, the researchers observed their motor development in their homes and conducted a follow-up session when they began to crawl. In addition, the parents recorded their babies' development stages before and between the two observations.
Seasons affect 'window of opportunity' to crawl
To track the development of the babies, the team used the Alberta Infant Motor Scale (AIMS), which is a highly reliable observational assessment that relates to four positions: prone (stomach), supine (back), sitting and standing.
Overall, the average age the babies from the study began to crawl was 31 weeks.
However, the researchers found that babies born in the winter - who began crawling in the summer - started crawling at an average age of 30 weeks, compared with those born in the summer, who started crawling at an average age of 35 weeks.
The team reports that there were no differences between boys and girls or in the initial method of crawling, which was consistently belly crawling or using hands and knees.
In detail, the overall AIMS score for babies born in the winter was higher, as was the score for movement in the prone position, which is the most meaningful score connected with crawling. However, there was no difference among the two groups for scores in the supine position, sitting or standing.
The researchers say their findings show there is a "window of opportunity" for beginning to crawl, and they point to the effects of seasons on crawling:
"The difference in crawling onset of 4 weeks constitutes 14% of a 7-month-old's life and is significant. Documenting the trend by comparing the results of a standard evaluation scale strengthens the findings and points to a significant seasonal effect in the Israeli context."
Home environment changes due to seasons are the key
But they note that the actual geographic location - and the associated climate - of the study is important in light of their findings, because such a seasonal effect is only observed in places where home environment differences between the seasons are substantial.
For example, the researchers say studies conducted in Denver, CO, and Osaka, Japan, found a similar seasonal effect to that of their recent study, whereas one conducted in Alberta, Canada - where home environment is fairly consistent all year round - did not yield the same seasonal effect.
"Although the winter in Israel is comparatively mild compared to other places in the world," note the researchers, "it turns out that it nonetheless influences the motor development of babies because of the differences between summer and winter in Israel."
They add that seasons influence, for example, the layers of clothing that babies wear. As such, babies born in the summer who are starting to crawl in the winter could be restricted by these clothing layers, hours of activity and daylight.
The team adds that parents should be aware of this seasonal effect so they can compensate and try to give their babies better opportunities for movement and development in the winter.
Medical News Today recently reported on a study that suggested parental attentiveness to infant babbling speeds up their language development.