Histomorphological changes in low-birth-weight term placentae and association with maternal factors: a comparative cross-sectional study

Low birth weight (LBW), defined by the World Health Organization (WHO) as a birth weight < 2500 g, remains as an important contributor to perinatal morbidity and mortality. Among term pregnancies (37 weeks to 41 weeks plus 6 days of gestation), LBW may reflect impaired placental support for fetal growth. This study compared gross and microscopic placental histomorphological changes between term LBW and normal birth weight (NBW; 2500-3999 g) placentae using Amsterdam Placental Workshop Group Consensus criteria (Amsterdam criteria) and evaluated their associations with selected maternal clinical factors.

This comparative cross-sectional study was conducted at a tertiary care hospital from September 2021 to September 2022 and included 100 singleton term placentae, with 50 each in the LBW and NBW groups. Placentae were examined grossly and microscopically using Amsterdam criteria, and maternal clinical data were extracted from hospital records. Continuous variables were compared using the independent-samples t-test, while categorical variables were analyzed using the chi-square or Fisher's exact test as appropriate. Associations with placental abnormalities were evaluated using univariate analysis, with p < 0.05 considered significant.

Mean placental weight was lower in the LBW group than in the NBW group [407 ± 70 g, 95% CI 387-427 vs. 573 ± 47 g, 95% CI 560-587; p < 0.001]. Mean umbilical cord length was shorter in the LBW group [47 ± 7 cm, 95% CI 45-49 vs. 63 ± 7 cm, 95% CI 61-65; p < 0.001]. Maternal and fetal vascular malperfusion lesions were more frequent in LBW placentae, including increased syncytial knots (70% vs. 6%), villous paucity with thin villi (54% vs. 14%), intramural fibrin deposition with venous ectasia (34% vs. 8%), and stem vessel obliteration (18% vs. 0%) (all p < 0.05). In univariate analysis, chronic hypertension was associated with maternal vascular malperfusion, was more common in the LBW group [11 (22%) vs. 1 (2%); p = 0.002].

Term LBW placentae showed lower placental weight, mean umbilical cord length was shorter, and more frequent vascular malperfusion lesions, suggesting that maternal and fetal vascular malperfusion are important placental lesions associated with LBW at term. Chronic hypertension was the only maternal clinical factor associated with LBW. Placental examination may help explain LBW retrospectively, while prospective prediction requires larger studies incorporating antenatal clinical data, Doppler findings, fetal growth parameters, and neonatal outcomes.