Reviewer ’s report  
 
Title: Serum 25 hydroxyvitamin D levels and affecting factors among preconception fertile  
women  
 
Version: 0 Date: 04 Feb 2020  
 
Reviewer: Research Square Reviewer 1  
 
Reviewer's report:  
 
PEER REVIEWER ASSESSMENTS:  
 
OBJECTIVE - Full research articles: is there a clear objective that addresses a testable research 
question(s) (brief or other article types: is there a clear objective)?  
Yes - there is a clear objective  
 
DESIGN - Is the current approach (including controls  and analysis protocols) appropriate for the 
objective?  
No - there are minor issues  
 
EXECUTION - Are the experiments and analyses performed with technical rigor to allow 
confidence in the results?  
No - there are major issues  
 
STATISTICS - Is the use of sta tistics in the manuscript appropriate?  
No - there are issues with the statistics in the study  
 
INTERPRETATION - Is the current interpretation/discussion of the results reasonable and not 
overstated?  
No - there are major issues  
 
OVERALL MANUSCRIPT POTENTIAL  - Is the current version of this work technically sound? 
If not, can revisions be made to make the work technically sound?  
Maybe - with major revisions  
 
PEER REVIEWER COMMENTS:  
 
GENERAL COMMENTS: This is an interesting study but some revisions are still needed.  
 
REQUESTED REVISIONS:  
 
1- Continuous variables such as age and BMI need to be compared with vitamin D levels 
(another continuous variable) by tests such as correlation analysis. While proposing categories of 
age and BMI will make the analysis by t -test possible, this method is not sufficient.  
 
2- There may be several confounding factors with a potential impact on the associations 
presented here. Thus, in addition to ANOVA, for categorical variables, and correlations analysis, 
for continuous variable s, it is necessary to use tests such as analysis of covariance (ANCOVA) or 
partial correlation depending on the types of variants. Such analysis would allow for testing the 
significance of the associations while controlling the confounding factors. Without  analysis of 
confounding factors, the presented data would not be of a strong value.  
 
3- In line with the last comment, many confounding factors may be involved that have not 
been investigated in this study such as taking vitamin D supplements. Nevertheless , among the 
factors investigated, a particular confounding factor would be the season of sampling. This could 
simply affect the results due to the level of sun exposures. For instance, non -working women may 
have higher levels because most of the samples fr om this group happened to be obtained in 
summer. Together, a complete revision of statistical analysis is required.  
 
Minor Comments:  
 
1- It is recommended to use numbers together with percentage for the data presented for 
example in the first paragraph of the Result section  
 
2- Several grammatical and syntax errors are found throughout the manuscript. I would 
recommend consulting an English -speaking editor familiar with the biological concepts for 
corrections.  
 
Are the methods appropriate and  well described?  
If not, please specify what is required in your comments to the authors.  
 
No 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the authors.  
 
No 
 
Are the conclusions drawn adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
No 
 
Are you able to assess any statistics in the manus cript or would you recommend an additional 
statistical review?  
If an additional statistical review is recommended, please specify what aspects require further  
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
 
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Needs some l anguage corrections before being published  
 
Declaration of competing interests  
Please complete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five years received reimbursements, fees, funding, or salary fr om an 
organisation that may in any way gain or lose financial ly from the publication of this 
manuscript, either now or in the future?  
 
2. Do you hold any stocks or shares in an organisation t hat may in any way gain or lose 
financially from the publication o f this manuscript, either now or in the future?  
 
3. Do you hold or are you currently applying for any patents  relating to the content of the 
manuscript?  
 
4. Have you received reimbursements, fees, funding, or salary from an organization that holds 
or has app lied for patents relating to the content of the manuscript?  
 
5. Do you have any other financial competing interests?  
 
6. Do you have any non -financial competing interests in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare t hat I have no competing interests' below.  
If your reply is yes to any, please give details below.  
 
This reviewer has been recruited by a partner organization, Research Square. Reviewers with 
declared or apparent competing interests are not utilized for t hese reviews. This reviewer has 
agreed to publication of their comments online under a Creative Commo ns Attribution License 
attributed to Research Square and was paid a small honorarium for  completing the review within 
a specified timeframe. Honoraria for reviews such as this are paid regardless of the reviewer  
recommendation.  
 
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I agree for my report to be made available under an Open Acc ess Creative Commons CC-BY 
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I agree to the open peer review policy of the journal