Dear Dr. Agampodi,

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.

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ACADEMIC EDITOR:

The authors are to be commended for the successful submission of this manuscript, which addresses an important area of research with potential implications for maternal and fetal health. The use of a population-based prospective cohort design is a notable strength.<o:p></o:p>

However, there is some ambiguity regarding the timing of participant recruitment. While it is stated under the "Procedure" section (line 153) that recruitment occurred during the first trimester, it is also mentioned (lines 146–147) that serum cortisol levels were available only for 1,290 participants who attended follow-up visits in the second or third trimester. Although the authors refer to a previously published methodology, it would greatly improve the clarity of the current manuscript to explicitly state when participants included in this analysis were initially recruited. Clear delineation of the recruitment timeline would aid in understanding the study design and cohort selection.<o:p></o:p>

Please submit your revised manuscript by Aug 08 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're 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.

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We look forward to receiving your revised manuscript.

Kind regards,

Surangi Jayakody, MBBS, MSc, MD

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

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2. Thank you for stating in your Funding Statement:

“The original cohort study was supported by the Accelerating Higher Education Expansion and Development (AHEAD) Operation of the Ministry of Higher Education, Sri Lanka funded by the World Bank [grant number DOR STEM HEMS [6026-LK/8743-LK]]. The funding agency has no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.”

Please provide an amended statement that declares *all* the funding or sources of support (whether external or internal to your organization) received during this study, as detailed online in our guide for authors at http://journals.plos.org/plosone/s/submit-now.  Please also include the statement “There was no additional external funding received for this study.” in your updated Funding Statement.

Please include your amended Funding Statement within your cover letter. We will change the online submission form on your behalf.

3. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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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?

Reviewer #1: Partly

Reviewer #2: Yes

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

Reviewer #1: Yes

Reviewer #2: I Don't Know

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

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: I read the presented manuscript with great interest. I wish to commend the authors in presenting a large data set from a LMIC set up which is a difficult task to accomplish. The study presents descriptive data of maternal serum cortisol levels in a large cohort of pregnant women in the second trimester.

I have only a few comments to make.

1. Please highlight the fact that ALL women in the cohort had their cortisol levels with-in the accepted reference range for the gestation.

2. I agree with the authors that the relationship with EPDS score and maternal serum cortisol levels may not have shown a correlation due to the chronology of the measurements. Please make a clear statement of when the EPDS score was obtained and when the serum cortisol level was measured- what was the time difference between the two measurements.

3. If the authors can present pregnancy outcome data, please check for fetal outcomes in relationship with second trimester cortisol levels - eg, previous authors have presented a relationship with high normal (>17) second trimester cortisol levels with adverse fetal outcomes. (The data will be an useful addition for a systematic review/ meta analysis)

Reviewer #2: Thank you for conducting this research and comprehensive article . This gives eye open for pregnancy and its related factors in developing country. I thought increase in cortisol levels in psychological stresses but it was not. Very interesting article . Best wishes for future endeavours

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Reviewer #1: No

Reviewer #2: Yes:  Dr. Chamara Wijemunige- Speciality Registrar in Obs & Gyne

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Normative serum cortisol levels in second and third trimesters and their associated factors: A prospective cohort study from Sri Lanka

PONE-D-25-16021R1

Dear Dr. Agampodi,

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

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Surangi Jayakody, MBBS, MSc, MD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments: