PONE-D-19-16639

Oral magnesium supplementation for leg cramps in pregnancy – a randomized controlled trial

PLOS ONE

Dear Dr. Alves,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised by all the reviewers.

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Kind regards,

Yiqing Song, MD, ScD

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes

Reviewer #4: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes

Reviewer #4: No

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes

Reviewer #4: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Yes

Reviewer #4: No

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I will focus on methods and reporting

Major

1) the introduction is very short for a research paper. Much more information is needed in terms of the background to the study.

2) I don't understand how the sizes of the groups differ so much following an 1 to 1 allocation process

3) the methods section is very poor. Power analyses are incomplete. What is the baseline level for cramps? power and numbers needed are very different between a very prevalent and a rare outcome. a 50% reduction is a a very large effect. What is the odds ratio? the analysis plan is pretty poor. Even if perfectly balanced why did they not analyse in the context of a logistic regression, where the effects could be quantified in ORs?

Minor

1) Abstract. 1 to 1 matching yes 50 vs 63 in the placebo group. that's not 1 to 1?

2) information on the blinding is needed in title and/or abstract. single? double?

3) abstract says the 2 groups were comparable. some elaboration is needed

4) no information on analyses methods in the abstract

5) no information on baseline levels in the abstract - only the reduction. we need some measure of the absolute, not only relative, reduction.

6) Abstract: report effects and their CIs rather than p-values

Reviewer #2: This is a randomized controlled trial to evaluate the effect of oral magnesium supplementation on leg cramps in pregnant women. There are many critical design flaws for this study. The data provided in the manuscript was not consistent in whole manuscript. Also, many writing issues and language questions presented in the manuscript.

I will list several important design flaws:

1. The ratio for randomization was 1:1, while the number of women in Mg supplementation group was 57 and 64 in the placebo group. The number of participants in two groups were imbalanced. And the author did not provide the detailed allocation concealment for randomization. This is very important in a RCT study. Without allocation concealment, randomization would be unsuccessful.

2. The sample size calculation was based on the estimation of 50% reduction in frequency of leg cramp in Mg treatment group. The primary outcome was the presence of the leg cramps. The current sample size might not be sufficient for detecting the differences in the primary outcome, since they calculated it according to the frequency of leg cramp. Additionally, the 50% reduction in frequency of leg cramp in treatment group might be too positive. All these above might be the reasons why this study had a negative result.

3. The method for missing values were not mentioned in the study.

Reviewer #3: 1. The hypothesis testing, power and type 1 error should be included in the study design section. Please also be clear whether the type 1 error is one-sided or two sided.

2. The screening failure rate is very high. Any reasons for this?

3. Could the authors perform some additional subgroup analyses to explore the effect of intervention?

Reviewer #4: In this RCT, oral magnesium did not reduce the occurrence nor frequency of leg cramp episodes in the second trimester of pregnancy. This is an interesting topic, but some details are missing from this manuscript.

1.) The rationale for the trial requires more explanation in the introduction to highlight any gaps in knowledge. For example, the Garrison et al. (2012) systematic reviewed showed no evidence that oral Mg is helpful for leg cramps during pregnancy, with low heterogeneity among trials. What will this RCT add?

2.) In the introduction, it would be more relevant to cite magnesium effects on muscle/ mechanistic effects rather than cite general information on the etiology of cramps.

3.) How common are cramps during the second trimester (study population used in the RCT)?

4.) pg. 5: Exclusion of those with Mg at baseline >9.5mmol/dL is not physiologically plausible given the Mg reference range.. this value is a typo?

5.) Was adherence self reported?

6.) How were outcomes ascertained?

7.) Additional statistical rationale for the sample size calculation is needed. Why was a 50% reduction in leg cramps expected?

8.) pg. 7: Lines 3-4: are units in mg/dL? Three serum levels are listed: should one be deleted?

9.) Provide information on whether any stopping rules were instituted (CONSORT missing item)

10.) Who was blinded to the information? (eg. only participants, their doctors, the PI, those assessing outcomes, the statistical analyst, etc)?

11.) Table 1: income values are approximately $50,000 annually? Units need checking

12.) Flowchart (Fig 1): Indicate which arm is the placebo; which is the Mg arm (currently unlabeled)

13.) Can the original Portuguese protocol be translated into English via an online translator or individual? The English summary of the protocol is an abbreviated version of the manuscript and provides no additional detail.

14.) The overall manuscript would benefit from copyediting before resubmission

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

Reviewer #4: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

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PONE-D-19-16639R1

Oral magnesium supplementation for leg cramps in pregnancy – a randomized double-blind controlled trial

PLOS ONE

Dear Dr. Alves,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

We would appreciate receiving your revised manuscript by Dec 23 2019 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Yiqing Song, MD, ScD

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

Reviewer #3: All comments have been addressed

Reviewer #5: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: No

Reviewer #3: Yes

Reviewer #5: No

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: No

Reviewer #3: Yes

Reviewer #5: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

Reviewer #3: Yes

Reviewer #5: No

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: No

Reviewer #3: Yes

Reviewer #5: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: 2. For sample size calculation: You have not answer my question yet. The primary outcome is the presence of leg cramps, while the outcome used for calculating sample size is the secondary outcome. This is a substantial issue for your protocol. That means your current sample size might be only sufficient for analysis of your secondary outcome. Also, please provide your function for sample size calculation. The reference Currently the 20% dropout rate is a little bit large. And I do not find a 50% reduction in your referent papers. Please have a check.

3. For missing value: In your flwo chart, all 66*2 were included into your analysis, however, in your table 2 only 64 in treatment and 64 in control group were included into analyses. While actually, the overall number of placebo is 66. Please re-check your numbers. Many other inconsistences in your manuscript. For example, in tbale 1, 36 in Mg group and 30 in placebo group were currently employed; while in total, 68 were currently employed. In table 2, 27,2 should be 27.2. Please check your manuscript thoroughly.

Reviewer #3: (No Response)

Reviewer #5: The authors aimed to evaluate to evaluate the effect of magnesium supplementation for the prevention of leg cramps in pregnant women.

According to information provided by the authors, the study was part of the Brazil MAGnesium trial and registered at ClinicalTrials.gov (Identifier NCT02032186). The registration refers to the Brazil MAGnesium trial, but neither the current study is referred to nor are the aims of the study defined as secondary outcomes. Therefore, the presented manuscript describes an unplanned secondary analysis of the above mentioned randomized trial Brazil MAGnesium trial. A secondary analysis should be regarded as an observational trial and should be identified explicitly as such.

The CONSORT checklist does not longer correspond to the presented study. The STROBE checklist would be more appropriate and will guide the authors to important aspects, which should be included in the description of the study. E.g. the consideration of potential confounders in the statistical analysis of observational data is necessary and should be added.

One further aspect is, that randomization corresponds to the estimated sample size (2000 assigned to magnesium, 1000 assigned to placebo (with 2:1 allocation ratio) according to protocol on ClinicalTrials.gov) and not to the subsample of 132 patients (with an apparent 1:1 allocation ratio). This means, that the quality characteristics of randomization no longer apply. The study is merely an observational trial.

The sample size of the initial study is based on the primary outcome (perinatal composite outcome). Therefore, the sample size and corresponding power is not adequate for the current outcome (presence of leg cramps) and puts the validity of the analysis and subsequent conclusion into question.

Apart from that, the “new” calculation is based on “50% reduction of leg cramps” and not on the variable defined as the primary endpoint (presence of leg cramps) so that the methodological basis of the study in itself is also questionable.

I am sorry to say, but from my point of view there are unsurmountable methodological deficits.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #2: No

Reviewer #3: No

Reviewer #5: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

Oral magnesium supplementation for leg cramps in pregnancy – an  observational  controlled trial

PONE-D-19-16639R2

Dear Dr. Alves,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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With kind regards,

Yiqing Song, MD, ScD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

The critiques by the reviewers have been nicely addressed and the manuscript has been improved significantly.  

Reviewers' comments: