Comparison of Fetal Thymus Size between Pregnant Women with Diabetic and Non-Diabetic Disease

Walaipan Supattanarungsi, MD¹,² ORCID , Monyada Pleankong, MD¹ ORCID , Wiyada Luangdansakul, MD¹ ORCID , Buppa Smanchat, MD¹ ORCID , Kornkarn Bhamarapravatana, PhD³ ORCID , Komsun Suwannarurk, MD⁴ ORCID

Affiliation : ¹ Department of Obstetrics and Gynecology, Bhumibol Adulyadej Hospital, Royal Thai Air Force, Bangkok, Thailand; ² Department of Obstetrics and Gynecology, Faculty of Medicine, Burapha University, Chonburi, Thailand; ³ Department of Preclinical Sciences, Faculty of Medicine, Thammasat University, Pathum Thani, Thailand; ⁴ Department of Obstetrics and Gynecology, Faculty of Medicine, Thammasat University, Pathum Thani, Thailand

Abstract
Objective: To compare fetal thymus size between fetuses of diabetic and non-diabetic pregnant women and to explore the relationship between thymus size, maternal diabetes type, glycemic control, and pregnancy outcomes.
Materials and Methods: This prospective study at Bhumibol Adulyadej Hospital included singleton pregnancies between 28 and 34 weeks, with participants divided into control (118 participants) and diabetic (121) groups. Fetal thymic diameter (TD) and thymic thoracic ratio (TTR) were measured via ultrasound. The diabetic group was further classified into pregestational diabetes mellitus (PGDM), GDMA1, and GDMA2. Maternal blood sugar control and HbA1c levels were recorded. Pairwise comparisons with Bonferroni correction identified differences between diabetes types, and receiver operating characteristic (ROC) curve analysis determined the cutoff for fetal thymus size.
Results: Among 239 participants, fetuses in the diabetic group had significantly smaller thymus sizes compared to the control group (TD: 32.7 vs. 33.9 mm, TTR: 0.34 vs. 0.40, p<0.05). The TTR was significantly lower in PGDM and GDMA2 subgroups than in non-diabetic pregnancies. Poor glycemic control and HbA1c ≥7% was associated with a significantly lower TTR but not TD. ROC analysis identified a TTR cutoff of ≤0.34 (AUC 71%) as a better predictor of fetal thymic size reduction than TD (AUC 58%). Neonatal complications, including higher birth weight, NICU admission, and early neonatal jaundice, were more prevalent in the diabetic group.
Conclusion: Fetal thymus size in pregnant women was significantly smaller than that of non-diabetic pregnant women. TTR was an effective measurement to detect the decrease in fetal thymus size.

Received 17 April 2025 | Revised 20 March 2026 | Accepted 23 March 2026
J Med Assoc Thai 2026;109(6):505-12
DOI: 10.35755/jmedassocthai.2026.6.03010

Keywords : Fetal thymus gland; Thymic diameter; Thymic thoracic ratio; Diabetes mellitus; Pregnancy


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