Babies born in winter start crawling earlier than those born in summer

The research was conducted by Dr. Osnat Atun-Einy of the University's Department of Physical Therapy and Dr. Dina Cohen, Moran Samuel and Prof. Anat Scher of the Department of Counseling and Human Development. 47 healthy babies with typical development patterns where divided them into two groups. The first group comprised "summer-fall" babies, 16 babies born from June to November, and the second, "winter-spring" babies, 31 babies born from December to May. The study consisted of motor observations in the babies' homes when there were seven months old, and a follow-up session when they began to crawl. Parents were asked to record the stages in their babies' development before and between the observations.

The study used the Alberta Infant Motor Scale (AIMS), an observational assessment with high reliability, to track the babies' development. The scale relates to four positions: Prone (on the stomach), supine (on the back), sitting, and standing. The average age at which the babies started crawling was 31 weeks. But while the babies born in the winter (who started to crawl in the summer) started to crawl at an average 30 weeks, those born in the summer (who started to crawl in the winter) began crawling at an average of 35 weeks, with no differences noted between the boys or the girls or in the initial style of crawling (belly crawling or using hands and knees).

The overall AIMS score was higher for those babies born in the winter, and the score for movement in the prone position, the scale most meaningful in connection with crawling was, significantly higher for the babies in the winter group. By contrast, there was no significant difference in the scores for the supine position, sitting, or standing between the two groups. According to the researchers, the findings strengthen the assumption that there is a window of opportunity for starting to crawl and stress the effect of the season on the start of crawling.

"The difference in crawling onset of four weeks constitutes 14 percent of a seven-month-old's life and is significant," the researchers note. "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.

"The geographic location and the local climate where the study is conducted is important to understand the findings, they add. A seasonal effect is found in places where the differences in the home environment between summer and winter are significant. Studies done in Denver, Colorado and in Osaka, Japan found a seasonal effect that corresponds with the findings of the Haifa study, but a study conducted in Alberta, Canada, where winters are long and cold on the one hand, but the home environment (because of winter heating) is very similar all year round, the seasonal effect was not observed.

"Although the winter in Israel is comparatively mild compared to other places in the world, it turns out that it nonetheless influences the motor development of babies because of the differences between summer and winter in Israel," the researchers say. "The season influences the babies' experiences in a number of ways, including layers of clothing that are worn; the opportunities babies are given to spend on the floor on their stomachs, and the hours of activity and daylight. Awareness of the seasonal effect is important so that parents will give their babies proper movement and development opportunities in the winter as well," the researchers say.