Clinical Appraisal of "Micronized Vaginal Progesterone Dose and Serum Progesterone Thresholds Determine Reproductive Outcomes in Frozen-Thawed Embryo Transfer With Hormone Replacement Therapy"

I-Hsuan Wu, Juan-Enrique Schwarze, Schwarze JE, Christoph Helwig, D'Hooghe T, Thomas D'Hooghe, Ilka Schellschmidt, Schellschmidt I
Reproductive medicine and biology · 2026 · vol. 25(1) , pp. e70088 · doi:10.1002/rmb2.70088 · PMID:42625845 · PMC13490851
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This critique evaluates a study on vaginal progesterone thresholds in frozen embryo transfer, highlighting methodological flaws including non-random allocation, unaddressed temporal confounding, and limited clinical applicability.

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This article is a clinical appraisal of a previous study concerning micronized vaginal progesterone dosing and serum thresholds in frozen-thawed embryo transfers. It highlights that the original authors have no disclosures to report, while noting that several co-authors are employees or shareholders of Merck KGaA, which provided financial support for the research. The appraisal also clarifies that no datasets were generated or analyzed during this specific commentary, meaning data sharing is not applicable. Relevance to endometriosis: This paper focuses on assisted reproductive technology outcomes and does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.

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Abstract

This paper critically evaluates Sekiguchi et al.'s study of vaginal progesterone dose, serum progesterone thresholds, and reproductive outcomes in hormone replacement therapy frozen embryo transfer (HRT-FET) cycles. The study conflates descriptive, predictive, and causal aims without a clearly prespecified primary question, limiting interpretability. Major concerns include non-random treatment allocation, potential residual confounding, absence of a causal framework for covariate selection, unaddressed temporal confounding related to Japan's 2022 insurance reform, and exclusion of an available progesterone formulation. Additionally, formulation specific pharmacokinetics, single-time-point progesterone measurement, and internally derived thresholding limit comparability, predictive validity, and clinical applicability.
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Ack

The authors would like to thank Yukti Singh, M. Pharm (Merck Specialties Pvt. Ltd., Bangalore, India, an affiliate of Merck KGaA, Darmstadt, Germany) for providing medical writing and editorial support, which was funded by Merck KGaA, Darmstadt, Germany.

Data

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

Ethics

The authors have nothing to report.

Consent

The authors have nothing to report.

Funding

Financial support was provided by Merck KGaA, Darmstadt, Germany.

Conflicts

I‐Hsuan Wu, Juan‐Enrique Schwarze, Ilka Schellschmidt, Christoph Helwig, and Thomas D'Hooghe are employees of Merck Healthcare KGaA, Darmstadt, Germany. Christoph Helwig owns shares of Merck KGaA.

Associated Data

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

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chemicals 6
progesterone progesterone progesterone progesterone progesterone progesterone

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