Fetal Adrenal Gland Biometry and Middle Adrenal Artery Doppler in Pregnancies Presenting with Preterm Labor: A Prospective Case–Control Study

<b>Objective</b>: This study aimed to compare fetal adrenal gland volume (AGV), fetal zone (FZ) depth, and middle adrenal artery pulsatility index (MAA-PI) between pregnancies presenting with preterm labor and gestational age-matched asymptomatic controls, and to evaluate size-adjusted adrenal metrics (corrected AGV [cAGV] and fetal zone-total gland depth ratio) in relation to gestational age at delivery and neonatal outcomes. <b>Methods</b>: This prospective analytical cross-sectional (case-control) study included 60 singleton pregnancies (30 with preterm labor and 30 asymptomatic controls) evaluated at a tertiary perinatology unit between 24 + 0 and 36 + 6 weeks' gestation. Transvaginal cervical length and transabdominal fetal adrenal measurements (AGV, FZ depth, and MAA-PI) were obtained at enrollment. Estimated fetal weight (EFW) at the index scan was retrieved, and corrected AGV (cAGV = AGV/EFW) and fetal zone-total gland depth ratio were calculated. Outcomes were gestational age at delivery, birthweight, Apgar scores, and neonatal intensive care unit (NICU) admission. Nonparametric group comparisons and Spearman correlations were used. <b>Results</b>: Gestational age at ultrasound was identical between groups (median 31 + 6 weeks). Compared with controls, the preterm labor group had shorter cervical length (12.5 vs. 33.5 mm, <i>p</i> < 0.001), higher AGV (1.53 vs. 1.08 cm³, <i>p</i> < 0.001) and FZ depth (7.45 vs. 5.30 mm, <i>p</i> < 0.001), and lower MAA-PI (1.11 vs. 1.46, <i>p</i> < 0.001). EFW at the index scan did not differ between groups (<i>p</i> = 0.900). Corrected AGV (cAGV) was higher in the preterm labor group (0.87 (0.76-1.06) vs. 0.59 (0.51-0.70), <i>p</i> < 0.001), and the fetal zone-total gland depth ratio was higher (0.328 (0.312-0.346) vs. 0.263 (0.241-0.278), <i>p</i> < 0.001). The preterm labor group delivered earlier (33 + 0 vs. 36 + 2 weeks, <i>p</i> < 0.001), had lower birthweight (1875 vs. 3188 g, <i>p</i> < 0.001), and more frequent NICU admission (50.0% vs. 6.7%; odds ratio 14.0, 95% CI 2.82-69.56; <i>p</i> < 0.001). Within the preterm labor group, gestational age at delivery correlated positively with cervical length (ρ = 0.900) and MAA-PI (ρ = 0.770) and negatively with AGV (ρ = -0.770) and FZ depth (ρ = -0.733), all <i>p</i> < 0.001; correlations were stronger for cAGV (ρ = -0.953, <i>p</i> < 0.001). <b>Conclusions</b>: Enlarged fetal adrenal gland volume and fetal zone depth together with reduced middle adrenal artery pulsatility index are associated with preterm labor and earlier delivery. Size-adjusted adrenal metrics (cAGV and fetal zone-total gland depth ratio) remained significantly different between groups, supporting these measures as potential adjuncts for risk stratification at presentation.