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

Objective

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.

Methods

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.

Results

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, p < 0.001), higher AGV (1.53 vs. 1.08 cm3, p < 0.001) and FZ depth (7.45 vs. 5.30 mm, p < 0.001), and lower MAA-PI (1.11 vs. 1.46, p < 0.001). EFW at the index scan did not differ between groups (p = 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), p < 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), p < 0.001). The preterm labor group delivered earlier (33 + 0 vs. 36 + 2 weeks, p < 0.001), had lower birthweight (1875 vs. 3188 g, p < 0.001), and more frequent NICU admission (50.0% vs. 6.7%; odds ratio 14.0, 95% CI 2.82-69.56; p < 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 p < 0.001; correlations were stronger for cAGV (ρ = -0.953, p < 0.001).

Conclusions

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.