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Announcement on benefits of walking to improve pregnancy outcomes relies heavily on secondary analysis

For women with history of pregnancy loss, walking may aid chance of becoming pregnant

Our Review Summary

This release summarizes a study that examined the impact of physical activity on a very narrow subgroup of women: those who have had 1-2 miscarriages and hope to become pregnant.

The findings suggest that vigorous activity in these women — and walking over 10 minutes at a time in those who were overweight — increases the chances for getting pregnant.

The news release clearly lays out most of the limitations of the study, the big one being its reliance on secondary analysis. While the release could have put more emphasis on the weaknesses of such evidence, we do note that the news release made it clear that the findings from this very small subgroup may not apply to all women hoping to conceive, and that more research is needed to explain why certain activities (but not all) improve the odds for conception.


Why This Matters

Many women who are trying to have children have been unable to do so in the past, some because of miscarriages. Any intervention which enhances the chances of conceiving — especially one that is easily accessible, and likely more healthy than harmful — would be welcome news.

If research suggests such an intervention exists, but there are significant limitations to consider (as with this study), then being clear about those limitations, and using cautious language (as this news release does) is preferable.

For reasons listed below it’s highly unlikely that the study referenced here will provide most women trying to get pregnant with much new or actionable information. From a very practical perspective, most physicians recommend their patients maintain a healthy weight and exercise regime, whether they are trying to get pregnant or not.


Does the news release adequately discuss the costs of the intervention?


The news release states:

Walking has great potential as a lifestyle change because of its low cost and availability

Fair enough.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The news release mentions two benefits of physical activity with regards to “fecundability” (the ability to become pregnant):

  1. Walking at least 10 minutes at a time improved fecundability in overweight woman (defined as a body mass index, or BMI, > 25)
  2. Vigorous physical activity (>4 hours/week) was also associated with improved chances of becoming pregnant

So the study put into context the amount of physical activity associated with an increase in fertility rates but it didn’t tell us how much more likely vigorous walkers were to conceive compared to those who didn’t walk, or those who walked only a little.

Does the news release adequately explain/quantify the harms of the intervention?

Not Applicable

Harms from walking are likely not significant enough to warrant mention here.

Here’s a minor point:  since vigorous activity is noted as beneficial to conception, this might warrant mention as something that a woman with other health concerns might consider consulting her doctor about.

Otherwise, the issue of harms seems negligible enough to consider this N/A.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

It’s important to realize that the benefits mentioned in this study were found by way of a “secondary analysis” of data from a much larger, multi-center trial in which the primary research question had to do with aspirin use and pregnancy. A secondary analysis is simply using existing data to retrospectively explore an alternate question that’s distinct from the original research.

The news release does allude to this being a secondary analysis but doesn’t explain that such analyses usually lack the statistical power of findings related to the primary research question.

Importantly, the 1,214 study subjects had a history of 1-2 miscarriages, and the release does well in mentioning that findings from this unique sub-group may not generalize to all women trying to conceive. Another limitation is also included:

That physical activity is related to other behaviors and lifestyle factors, and women who are more physically active may be different from women who are less active in many ways.

Although the research attempted to adjust for these differences (called “confounding variables”) they could not do so completely. This was noted in the study and could have been pointed out in the release as an important limitation. (For more information on why reporting on variables is important see our post and video on a diet soda study that had some of the same issues.)

Another limitation that was not mentioned in the release is how physical activity — which is a key measurement in this study — was measured. It relied upon activity questionnaires completed by the women. These are not always reliable and can limit the significance of the findings.

Does the news release commit disease-mongering?


No disease mongering.

Does the news release identify funding sources & disclose conflicts of interest?


The study funders are listed on a sidebar on the EurekAlert! site, where the release is hosted. We encourage news releases to include funders and any conflicts of interest in the body of the release so that the information is carried over by news organizations or blogs running the release verbatim.

The published paper lists no conflicts of interest among the authors.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

What other types of physical activity were measured? Many women might be left wondering if other forms of exercise are just as good as walking. It might have helped to clarify this (and if the study did not address this, then make that clear to readers). It would also help readers to note what the “dose” of exercise was that was associated with a positive effect on fertility.

There is a statement included from the lead author that could confuse people:

One of our main findings is that there was no overall relationship between most types of physical activity and the likelihood of becoming pregnant for women who had already had one or two pregnancy losses [except for walking, which was associated with higher likelihood of becoming pregnant among women who were overweight and obese.

That’s a lot of caveats! And many women — overweight or not, with previous miscarriages or not — might be left wondering if their form of exercise helps or hinders their chances at conception.

Does the news release establish the availability of the treatment/test/product/procedure?


As noted above, the release mentions walking as both easily accessible and a potentially modifiable factor for those trying to get pregnant.

Does the news release establish the true novelty of the approach?

Not Satisfactory

Although the study authors provides a nice summary of other research in which the results do and do not agree with their study, this is not included in the news release and would have been a helpful addition.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?


In general, this news release does a very good job of using cautious language. However, it should have avoided the cause-and-effect language implied by the use of the words “may aid” in the headline, particularly since this was a secondary analysis of earlier research into side effects of aspirin use during pregnancy, not a randomized controlled trial of walking during pregnancy. The latter type of study might have warranted the more causal language.

We did appreciate the inclusion of the final sentence:

Further study is necessary to clarify possible mechanisms through which walking and vigorous activity might affect time-to-pregnancy.


Total Score: 5 of 9 Satisfactory


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