Tuesday November 24 2009
“Having children could slow down the progression of multiple sclerosis (MS),” The Independent reported. It said researchers have found that, compared to women with MS who have never had children, those who had children after the onset of the disease were 39% less likely to have progressed to a stage where they needed assistance when walking 100m.
This research looked at the medical records of women attending an MS clinic in Belgium. The study has a number of limitations. For example, rather than childbirth slowing down the progress of MS, an alternative explanation of the results is that women who have less severe MS are more likely to decide to have children than those who have a faster-progressing disease.
Due to the study's limitations, it does not provide conclusive evidence of the effects of pregnancy on the long-term progression of MS. Larger studies that examine this question are needed.
Where did the story come from?
The research was carried out by Dr M B D’hooghe and colleagues from the National MS Centre (Nationaal MS Centrum) in Belgium and other research centres in Belgium and the Netherlands. No sources of funding were reported for the study, and the researchers declared that they had no conflicts of interest. The study was published in the peer-reviewed Journal of Neurology, Neurosurgery and Psychiatry.
This study was reported accurately by the BBC News website and The Independent. However, the BBC gave a more balanced report as it also provided important information about the study’s limitations.
What kind of research was this?
This study investigated how childbirth affects multiple sclerosis (MS) in the long term. Some previous studies have suggested that the risk of relapse in MS might reduce during pregnancy but then increase in the three months after giving birth. The researchers report that the long-term effects of pregnancy on MS progression are not clear.
The study was cross sectional, which means that the data were collected at one point in time. The data were collected from medical records, which allowed the researchers to identify when MS was first diagnosed, its severity over time, and details of any pregnancies the women had. As this data was not collected specifically for this study, there is a greater possibility that some of the information may be inaccurate or missing. A study that was set up to collect specific data prospectively would have been preferable.
What did the research involve?
The researchers used data from the medical records of 330 women attending their MS clinic. The women had had MS for an average of 18 years. The researchers grouped the women into those who did not have children (80 women), those who had children before they developed MS (170 women), those who had children after they developed MS (61 women), and those who had children before and after they developed MS (19 women).
The researchers were interested in when the women reached a specific level of MS severity. The scale they used to measure MS severity was the Expanded Disability Status Scale (EDSS), which ranges from zero (normal neurological function) to 10 (death from MS). The level the researchers were interested in was EDSS 6, which signifies a level of disability where the women needed assistance (e.g. with a cane) for at least part of a 100 metre walk.
The researchers compared how long it took the groups of women who had children at differing time points to reach EDSS 6 compared to women with no children. In this analysis, the researchers took into account the time when the women’s MS began.
Another analysis compared all women who had children with those without, as it can be difficult to say exactly when the biological process that results in MS starts. The researchers also specifically looked at women who developed MS before the age of 30, as these women were more likely to give birth after that age.
What were the basic results?
The women had MS for an average of 18 years, at which point just over half (55%) the women had reached the EDSS 6 level of severity. The proportion of each group that reached EDSS 6 was:
- 52% of the women who did not have children.
- 59% of those who had children before they developed MS.
- 51% of those who had children after they developed MS.
- 37% of those who had children before and after they developed MS.
The researchers found that women who had children after the onset of their MS tended to take longer to reach EDSS 6 than those who had no children. Some of this effect was due to the age at which the groups developed MS, but the difference was still significant even after this was taken into account (hazard ratio [HR] 0.61, 95% confidence interval [CI] 0.37 to 0.99). Women who had children at any time also took longer to reach EDSS 6 than women who did not have children (hazard ratio [HR] 0.66, 95% confidence interval [CI] 0.47 to 0.95).
Similar results were found when the researchers assessed only women who developed MS before the age of 30. However, the difference between the four groups did not reach statistical significance. This may have been due to the smaller number of women in this analysis.
How did the researchers interpret the results?
The researchers conclude that their results “seem to support a possible favourable long-term effect of childbirth on the course of MS”, but that the results could be biased.
This research has a number of limitations that reduce the reliability of its results:
- As the authors acknowledge, they cannot exclude the possibility that women who have less severe MS are more likely to have children than those who have more severe MS. If this is the case, the severity of MS would affect the likelihood of having a baby, rather than childbirth affecting the severity of MS. The researchers did not have detailed information about how the severity of MS progressed over time or about the women’s reasons for not becoming pregnant, which could help them to determine whether this was the case.
- The women’s age at the onset of the disease also seemed to affect the results, as taking this into account reduced the size of the observed effect. To remove this problem, the researchers carried out analyses only in women who developed MS before the age of 30. Although these analyses still showed a trend towards a longer time to EDSS 6 in women who had children after the onset of MS, this effect was no longer significant. This may have been due to the smaller number of women in this analysis. These results will need to be confirmed in another study.
- The study was relatively small, which may reduce the reliability of its results. This small size may explain the wide confidence intervals around the hazard ratios, suggesting that these findings are not particularly robust.
- Medical records, from which this study obtained its data, are not always completely accurate and don’t always give the complete story. For example, women may have first gone to the clinic at different stages in their development of MS, and there may have been discrepancies in how the severity of their MS was assessed.
- The study did not take into account what treatments the women were receiving. The researchers say that immune system treatments for MS have only gradually come into use over the past 10 years, and for most of the study period would not have been used by the majority of the participants.
- Not all the women that were assessed had reached EDSS 6, and the results may have been different if all the women had been followed until they reached this stage.
Due to these limitations, this study does not provide conclusive evidence about the effects of pregnancy on the long-term progression of MS. Further studies will need to look at this question. These studies will preferably involve a group of women of similar ages shortly after they develop MS and will follow them up over time to monitor the severity of their MS.