Threatened preterm labor in Japan: an evidence-practice gap in diagnosis, tocolysis, and guideline implementation.

Preterm birth remains a major perinatal challenge, and management of women presenting with symptoms suggestive of early labor can shape admission, monitoring, medication use, and transfer pathways. In contemporary international practice, threatened preterm labor is generally managed within a risk-stratified framework, and tocolysis is used mainly for short-term obstetric purposes such as antenatal corticosteroid completion, maternal transfer, and fetal neuroprotection. In Japan, however, threatened preterm labor has often been diagnosed across a relatively broad clinical spectrum and managed with prolonged inpatient observation, bed rest, and extended ritodrine-based tocolysis. This review examines that pattern as a policy and practice problem rather than a narrow therapeutic controversy. It argues that the Japanese approach reflects a persistent evidence-practice gap involving broad diagnostic labeling, limited evidence supporting routine maintenance ritodrine, heterogeneous real-world practice, and guideline wording that remains more permissive than prohibitive. The available literature does not support prolonged maintenance ritodrine as routine care, while associations with maternal and neonatal safety concerns have been increasingly reported. Persistence is interpreted as potentially related to diagnostic breadth, institutional routines, limited therapeutic pathways, and uncertainty about de-escalation, not as evidence of a single cultural or medico-legal cause. This review proposes clearer negative recommendations on prolonged maintenance ritodrine, stronger diagnostic precision, and operational protocols that distinguish high-risk women requiring inpatient care from lower-risk women suitable for reassessment, treatment reduction, or outpatient follow-up.