Winter-born babies crawl 5 weeks earlier, study finds

Babies born in the winter start crawling earlier in life than do babies born in the summer, an Israeli study indicated.

The study found babies born in the winter started to crawl an average of five weeks earlier than those born in the summer – a significant difference at less than a year old.

The researchers behind the study, published in the Journal of Reproductive and Infant Psychology, say the difference seems to be that babies born in the winter have the advantage of summer weather at the stage when they are getting ready to crawl.

Conducted in Israel’s Mediterranean climate, the study helps explain early childhood development of motor skills and could help parents get their babies scooching along sooner, the researchers said.

“Awareness of the seasonal effect is important so that parents will give their babies proper movement and development opportunities in the winter as well,” said Dr. Osnat Atun-Einy, a physical therapist at the University of Haifa, who led the study.

Dr. Dina Cohen, Moran Samuel and Prof. Anat Scher of the Department of Counseling and Human Development collaborated on the research.

The researchers divided 47 healthy babies with typical development patterns into two groups: 16 “summer babies,” born between June and November, and 31 “winter babies,” born between December and May. They observed the babies’ motor development at 7 months and again when they began to crawl. Parents were asked to records the stages of their babies’ development from birth until the second observation.

The babies in the study started crawling at an average age of 31 weeks. But the summer and winter babies started crawling at significantly different times on average. The babies born in winter or spring started to crawl in the summer, at an average of 30 weeks; while the babies born in the summer or fall, started to crawl in the winter, at an average age of 35 weeks.

“The difference in crawling onset of four weeks [compared to the overall average] constitutes 14 percent of a 7-month-old’s life and is significant,” Atun-Einy said. “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.”

Data analysis revealed no differences in the groups’ initial crawling style – belly crawling versus using hands and knees. Nor were there differences between boys and girls.

The study used the Alberta Infant Motor Scale, or AIMS, a well-established observational assessment, to track the babies’ development. The scale relates to movement in four positions: lying on the back, lying on the stomach, sitting, and standing.

The winter babies had a higher average AIMS score due to significantly outperforming the summer babies in moving on their stomachs, the most meaningful scale in connection with crawling. The winter and summer babies did not differ significantly on the other scales.

The researchers said the findings strengthen the notion that there is a developmental “window of opportunity” for babies to start crawling. Season, they say, appears to play a role in how prepared babies are when that developmental window opens.

Babies may wear less clothing, be allowed to spend more time on the floor on their stomach, and have more hours of activity and daylight in the summer, they say. All these things could help set the stage for their first crawl.

Previous research has found similar results in places where the weather changes notably between summer and winter, such as in Denver, Colorado and in Osaka, Japan. On the other hand, a study done in Alberta, Canada, where winters are long and cold but heating keep the home environment steady year round, found no seasonal effect on the start of crawling.

The winter is Israel is relatively mild, but it is wetter and colder than the summer.