Related Experiment Video
Updated: May 11, 2026
A Method of Trigonometric Modelling of Seasonal Variation Demonstrated with Multiple Sclerosis Relapse Data
Published on: December 9, 2015
Month of birth and risk of multiple sclerosis in a Portuguese population
Pedro Barros1, Joaquim Marques de Sá, Maria José Sá
1Department of Neurology, Centro Hospitalar São João, 4200-319 Porto, Portugal. pedrojgbarros@gmail.pt
Background:
Several studies analyzing the month of birth (MOB) of multiple sclerosis (MS) patients and the risk of the disease have been published; as a whole, MS patients were found to be predominantly born in spring months, leading to the current assumption that MOB is somewhat related to the risk of MS.
Objective:
Estimate the risk of MS by MOB in a Portuguese population.
Methods:
MS patients sample was obtained from the database of patients attended at our MS clinic and born in the districts of Porto, Braga and Viana do Castelo. The control sample was composed of the live births records in the same time period and geographical area. We applied the Hewitt test for seasonality.
Results:
We found 421 patients that satisfied the conditions to enter the study. The rank-sums for successive 6-month segments indicate the July-December period as of higher incidence; however, the corresponding rank-sum (48) was not statistically significant according to the Hewitt test (p>0.05).
Conclusion:
Our data does not support the seasonality hypothesis of MOB as risk factor for MS in Portugal. However we are aware that the analysis of a larger MS sample could shed more light in this issue.
Insights
This study found no significant link between month of birth and multiple sclerosis (MS) risk in Portugal. The data does not support the hypothesis that birth season influences MS development in this population.
Area of Science:
- Neurology
- Epidemiology
Background:
- Previous studies suggest a link between month of birth (MOB) and multiple sclerosis (MS) risk, with a tendency for MS patients to be born in spring.
- This has led to the hypothesis that MOB may be a risk factor for MS.
Purpose of the Study:
- To investigate the association between month of birth and the risk of developing multiple sclerosis (MS) within a Portuguese population.
- To determine if seasonality in birth month influences MS incidence in Portugal.
Main Methods:
- A case-control study was conducted using a sample of MS patients from Porto, Braga, and Viana do Castelo.
- Control data were obtained from live birth records within the same geographical area and time period.
- The Hewitt test was employed to analyze birth seasonality.
Main Results:
- The study included 421 MS patients.
- Analysis indicated a higher incidence during the July-December period, but this finding was not statistically significant (p>0.05).
- The Hewitt test did not reveal significant seasonal patterns in birth month for MS patients.
Conclusions:
- The findings do not support the hypothesis that month of birth is a significant risk factor for multiple sclerosis in Portugal.
- A larger sample size may be required to further investigate potential subtle associations between birth seasonality and MS risk.
Related Concept Videos
01:19Multiple Sclerosis l: Introduction
01:12Relative Risk