Timing of Magnesium Sulfate Cessation and Apnea of Prematurity in Late‐Preterm Twin Infants

ABSTRACT Objective To evaluate the association between the timing of maternal magnesium sulfate (MgSO 4 ) discontinuation before delivery and the risk of apnea of prematurity (AOP) in late‐preterm twin infants. Methods This retrospective cohort study included 161 twin pregnancies (322 infants) delivered between 34 0/7 and 36 6/7 weeks at Yamanashi Prefectural Central Hospital (2017–2025). Infants with major anomalies or intrauterine fetal demise were excluded. The primary exposure was the interval between MgSO 4 cessation and delivery, categorized as: no exposure, < 12, 12–24, and ≥ 24 h. Two multivariable logistic regression models were constructed. Model 1 evaluated the association between any maternal MgSO 4 exposure and AOP. Model 2 further incorporated the timing of MgSO 4 discontinuation as a categorical exposure, adjusting for gestational age, chorionicity, small‐for‐gestational‐age status, sex, and 1‐min Apgar score. Results Among the 322 infants, 112 (34.8%) developed AOP. In Model 1, maternal MgSO 4 exposure itself was not significantly associated with AOP. However, in Model 2, delivery within 12 h after cessation of MgSO 4 was independently associated with AOP (adjusted odds ratio, 7.44; 95% confidence interval, 1.48–37.4), whereas longer discontinuation intervals (12–24 or ≥ 24 h) were not. Conclusions Among late‐preterm twin infants, maternal MgSO 4 exposure itself was not independently associated with AOP; however, delivery soon after MgSO 4 discontinuation was associated with an increased risk of AOP. These findings support consideration of MgSO 4 discontinuation timing in perinatal risk assessment and neonatal respiratory monitoring and may help guide future studies.