Background: Low birth weight (LBW) remains a major contributor to neonatal morbidity and mortality. Maternal body mass index (BMI) is widely used to identify pregnancies at risk of adverse birth outcomes; however, the optimal BMI classification for Asian populations remains uncertain. This study compared the WHO Global and WHO Asia-Pacific BMI classifications in identifying pregnant women at risk of delivering LBW infants. Methods: An unmatched case-control study was conducted among 729 pregnant women attending 10 primary healthcare centers in Jakarta, Indonesia. Cases comprised 368 women who delivered LBW infants (2,500 g), while 361 women with normal birth weight infants served as controls. Logistic regression models were developed using both BMI classifications and compared using the area under the receiver operating characteristic curve (AUC), Akaike Information Criterion (AIC), and Nagelkerke R². Screening performance was assessed using sensitivity, specificity, positive predictive value, and negative predictive value. Results: After adjustment for maternal age, preterm delivery, and pregnancy-induced hypertension, both BMI classifications showed comparable predictive performance (WHO Global: AUC=0.646; Asia-Pacific: AUC=0.634). BMI category was not independently associated with LBW in either model. However, using obesity as the screening threshold, the WHO Asia-Pacific classification demonstrated substantially higher sensitivity than the WHO Global classification (49.5% vs. 16.3%), although specificity was lower. Conclusions: Although both BMI classifications showed similar predictive performance, the WHO Asia-Pacific classification identified a substantially greater proportion of women at risk of delivering LBW infants. These findings support the use of population-specific BMI 2 thresholds to strengthen antenatal nutritional screening in Indonesian and other Asian populations.