Babies Conceived During Winter/Spring May Be at Higher Risk for Cerebral Palsy

Lara Salahi

September 22, 2023


Cerebral palsy affects 1 to 4 per 1000 live births in the United States. A new cohort study published in JAMA Open Network found children conceived during the winter and spring months appear to have a slightly higher risk for developing CP than those conceived during the summer. Fall months carried about the same or only slightly higher risk of CP than summer months.


  • Researchers examined data from nearly 4.5 million live births registered in California between 2007 and 2015, exploring if the season of conception could serve as an indicator of exposure to environmental risk factors.

  • For instance, infants conceived in winter months may have higher exposure to viruses like influenza. In California, agricultural pesticides are most often applied in summer months, when pregnant people would be in their first or second trimester and receive their most exposure to the fine particulates, the authors hypothesize.

  • Almost 4700 babies in the study population were diagnosed with CP. Researchers also considered the role of preterm birth as a potential mediating factor, and adjusted for sociodemographic characteristics such as maternal age, race, education, smoking during pregnancy, and body mass index.


  • The study found that children conceived in winter and spring had a 9% (95% CI, 1.01 - 1.19) to 10% (95% CI, 1.02 - 1.20) higher risk of developing CP than those conceived in the summer.

  • Children conceived in January, February, or May carried a 15% higher risk compared with babies conceived in July.

  • The risk was more pronounced among mothers with low education levels or living in neighborhoods where residents have high rates of unemployment, single-parent households, multi-unit households, and lower rates of high school graduates.


The researchers noted that possible explanations for the seasonal link to CP risk may include the prevalence of maternal infections during pregnancy, variations in exposure to pesticides, and seasonal patterns for air pollution. "Investigating seasonal variations in disease occurrence can provide clues about etiologically relevant factors," they write.


Lead author Haoran Zhou, MPH, Yale School of Public Health, and colleagues published their findings online today in JAMA Network Open. The study was partly supported by a grant from the American Academy for Cerebral Palsy and Developmental Medicine.


The study may not have fully captured all children with CP in the cohort due to the possibility of misclassification. The findings may not be generalizable beyond California. The overall increased risk associated with the season of conception was relatively small, suggesting family planning strategies may not need to change based on these findings. The exact mechanisms involving potential environmental factors need further investigation.


The authors report no relevant financial relationships.

For more news, follow Medscape on Facebook, X (formerly Twitter), Instagram, YouTube, and LinkedIn


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.