「産後の疲労感尺度Ver.2」におけるカットオフ値の検討：エジンバラ産後うつ病質問票との関連からみた一次スクリーニングツールとしての妥当性

Determining Cutoff Scores for the Postpartum Fatigue Scale Ver.2: Validity as a First-Line Screening Based on Edinburgh Postnatal Depression Scale Classification

抄録

【目的】産後の母親は、身体的・心理的に疲労しやすく、疲労感は抑うつのリスク要因となる。本研究では、疲労感の増悪に早期に気づき、支援につなげる手がかりとすることを目的として、「産後の疲労感尺度Ver.2」のカットオフ値をエジンバラ産後うつ病質問票（EPDS）得点との関連から検討した。

【研究方法】分析には、産後2週から4か月までの母親500名を対象とした既存のWeb調査データを用いた。産後の疲労感尺度Ver.2とEPDSを用いて、ROC曲線分析により判別精度を評価し、AUC、感度、特異度を算出した。Youden Indexに基づき最適なカットオフ値を導出し、さらに、得点を基準としたロジスティック回帰分析により、EPDS得点が疲労感に与える影響をオッズ比で検証した。

【結果】ROC分析の結果、産後の疲労感尺度Ver.2の最適カットオフ値は111点（AUC=0.836、感度0.642、特異度0.878）であった。感度重視の観点から再検討した結果、99点（感度0.839、特異度0.657）が一次スクリーニングにおいて、より実践的な基準と判断された。下位尺度「精神的ストレス状態」でも高い判別力（AUC=0.871、感度0.849、特異度0.772）を示し、抑うつ傾向の把握に有効であることが示唆された。ロジスティック回帰分析では、99点のオッズ比10.0、111点のオッズ比12.9であり、いずれも統計的に有意な関連が認められた。

【結論】本研究では、EPDS得点との関連から「産後の疲労感尺度Ver.2」のカットオフ値を検討し、99点および111点が高い判別力を示した。特に99点は感度が高く、一次スクリーニングに有用と考えられた。カットオフ値の設定は母親によるセルフモニタリングや支援者との認識の共有を促進するが、産後の時期によって疲労感の背景や表出の仕方が異なることから、カットオフ値の活用にあたっては、時期に応じた柔軟な運用が求められる。数値のみで判断するのではなく、母親の状態や生活背景を踏まえた支援が重要である。

Abstract

【Purpose】Postpartum mothers are in a state where fatigue tends to accumulate due to a combination of physical exhaustion from childbirth, hormonal fluctuations, frequent breastfeeding, sleep deprivation, and psychological stress. Many mothers tend to prioritize childcare, making it difficult for them to recognize their own fatigue or physical discomfort. In response to this issue, the author developed the Postpartum Fatigue Scale Ver.2 to objectively assess maternal fatigue. Users of the scale have requested interpretive guidelines, particularly a cutoff score to determine whether the level of fatigue warrants support. Therefore, the present study aims to statistically derive a cutoff score for the Postpartum Fatigue Scale Ver.2 and to construct a tool that can serve as a practical reference for both mothers and support providers.

【Method】This study analyzed existing data from a web-based, self-administered survey conducted in February 2021, with 500 mothers between 2 weeks and 4 months postpartum. Exclusion criteria were mothers separated from their infants or those with preexisting conditions such as diabetes, kidney disease, heart disease, or psychiatric disorders. The survey included the Postpartum Fatigue Scale Ver.2 and the Edinburgh Postnatal Depression Scale（EPDS）． Based on the EPDS cutoff score of 8/9, a receiver operating characteristic （ROC） curve analysis was performed. This analysis evaluated the predictive accuracy of fatigue scores for identifying mothers with high EPDS scores and calculated the area under the curve（AUC）， sensitivity, and specificity. The optimal cutoff value was determined using the Youden Index. Subsequently, logistic regression analysis was conducted using odds ratios and p-values to examine the influence of EPDS scores on fatigue levels. A similar analytical procedure was applied to the “Mental Stress State” subscale. All statistical analyses were performed using EZR software（version 1.68）．

【Results】The ROC analysis revealed that the total Postpartum Fatigue Scale Ver.2 score demonstrated strong discriminative ability, with an AUC of 0.836. The optimal cutoff score was 111, showing high specificity （0.878）， although the sensitivity was relatively low at 0.642. To prioritize practical utility as a first-stage screening tool, further analysis was conducted within the range of sensitivity ≥0.80. Consequently, a cutoff score of 99 was determined to be more appropriate. At 99 points, the sensitivity and specificity were 0.839 and 0.657, respectively. This indicated that the risk of overlooking cases was minimized, while sufficient discriminative power was maintained. Therefore, this score was considered a valid and practical threshold for early stage support. Logistic regression analysis showed that the odds ratio at 99 points was 10.0（95% CI: 5.740-17.600） and 12.9（95% CI: 7.830-21.200）at 111 points. Both of these demonstrated statistically significant associations. In addition, the “Mental Stress State” subscale showed strong discriminative ability, with an AUC of 0.871, sensitivity of 0.849, and specificity of 0.772.

【Conclusion】This study identified 99 points as a statistically valid cutoff score for the Postpartum Fatigue Scale Ver.2, supporting its use as a practical screening tool. This cut-off enables mothers to monitor their fatigue levels and recognize when to seek rest or support, thereby promoting self-care and facilitating timely interventions by healthcare providers. Although numerical thresholds offer clarity and accessibility, they may not fully capture the subjective and contextual aspects of maternal well-being. Therefore, it is essential to interpret the scores alongside mothers’narratives and lived experiences. Future research should examine the relationship between fatigue scores and actual support-seeking behaviors, assess the impact of interventions based on score changes, and explore the applicability of this scale in diverse cultural and generational contexts. Evaluating how the cutoff score is used in clinical settings and its influence on maternal awareness and support quality will be critical for refining the tool's practical value.