Comment on: Can prepregnancy BMI be used to detect the risk of sarcopenia in Japanese pregnant women?

Abstract

Plain language summary

To assess body mass index with bioimpedance analysis device may not reflect the real muscle mass in pregnancy so it can be assessed by ultrasound of thigh muscles. Life style factors and nutrition should also be checked in pregnant women besides muscle mass. Recognizing muscle failure early in pregnant women is essential to decrease the health risks for both mothers and their babies.

To the Editor,

We read with great interest the recent article by Miwa et al. at Women’s Health, entitled “Can prepregnancy BMI be used to detect the risk of sarcopenia in Japanese pregnant women?” The authors address a highly relevant and timely topic by drawing attention to the limitations of BMI-based classification in identifying sarcopenia risk during pregnancy. Their findings suggest that reliance on prepregnancy BMI alone may lead to underrecognition of sarcopenia in pregnant women. ¹

While we agree with the authors that assessment of body composition, rather than body weight alone, is more appropriate, we would like to offer several methodological considerations that may help refine the interpretation of the results and guide future research.

Although the authors assessed appendicular skeletal muscle mass rather than whole-body composition, the use of bioelectrical impedance analysis (BIA) may still have inherent limitations during pregnancy. BIA estimates muscle mass based on tissue electrical conductivity, which is strongly influenced by hydration status. ² Pregnancy is characterized by dynamic changes in total body water, extracellular fluid, and plasma volume, potentially affecting impedance-based measurements and leading to misestimation of skeletal muscle mass.

Moreover, skeletal muscle mass is not uniformly distributed throughout the body, and regional muscle assessment may provide more precise and clinically meaningful information. Ultrasound-based evaluation of specific muscle groups—such as the rectus femoris or biceps brachii—using measurements of muscle thickness, cross-sectional area, and echo intensity, as well as their combination, has demonstrated high diagnostic accuracy for sarcopenia.^3,4 As such, regional muscle ultrasound represents a reliable, radiation-free, and pregnancy-safe method that is relatively less affected by hydration-related changes and may effectively complement handgrip strength assessment. In addition, where feasible in a research setting, mid-thigh magnetic resonance imaging could offer detailed evaluation of both muscle quantity and muscle quality, providing further insight into maternal skeletal muscle status during pregnancy. ⁵ However, pregnancy-related edema may still influence ultrasound measurements; therefore, it should be interpreted alongside functional assessments such as handgrip strength.

Beyond methodological considerations, sarcopenia is increasingly recognized as a multifactorial condition, and lifestyle-related factors that impair muscle health warrant consideration during pregnancy. Established risk factors—including being unmarried, physical inactivity, malnutrition, smoking, alcohol consumption, and sleep disorders—have all been associated with sarcopenia. ⁶ Systematic assessment of these factors in pregnant women may provide a broader clinical perspective and help identify additional opportunities for early prevention in at-risk populations.

Finally, dietary protein intake—particularly adequate consumption of high-quality, leucine-rich protein—plays a critical role in the prevention and management of sarcopenia. In the study by Miwa et al., sarcopenia risk was evaluated primarily based on total caloric intake, without specific evaluation of dietary protein quantity and quality. However, protein intake at approximately 1.0–1.2 g/kg/day, especially when rich in leucine, is a well-established protective factor against sarcopenia and constitutes a cornerstone of both preventive and therapeutic strategies. ⁷ Given its pivotal role in stimulating muscle protein synthesis, assessment of protein quality and key amino acid intake may be more clinically informative than macronutrient proportions alone in this setting.

Nonetheless, evaluating sarcopenia during pregnancy remains important, as it has been associated with insulin resistance, gestational diabetes mellitus, and other adverse pregnancy outcomes. ⁸ However, the use of sarcopenia cut-off values derived from non-pregnant populations may limit the precision of sarcopenia classification in pregnant women. Although direct evidence supporting this limitation remains scarce, this concern is conceptually important and highlights the need for pregnancy-specific diagnostic thresholds.

In the study by Miwa et al., presarcopenia was identified in 100% of the underweight group and in 40% of the normal-weight group. These findings indicate that sarcopenia during pregnancy may be more prevalent than previously recognized and therefore merits further investigation. Furthermore, by suggesting an association between maternal sarcopenia and low birth weight, the study implies that impaired maternal muscle health may contribute to a biological substrate for long-term health risks in offspring, further underscoring the clinical relevance of this condition. ¹

In conclusion, this valuable study provides important evidence that BMI-based classification alone may fail to detect sarcopenia risk in pregnant women, underscoring the need for body composition–based assessment. Despite the methodological considerations outlined above, the authors should be commended for drawing attention to this condition during pregnancy. Their work represents an important step toward improving recognition of maternal muscle health and encouraging further research in this emerging field.