Bold statement: Gestational diabetes doesn’t just complicate pregnancy—it reshapes the fetal heart, and understanding how can help you spot trouble before it starts. But here’s where it gets controversial: not all doctors agree on using fetal heart volume measurements as a routine predictor for neonatal problems. Let’s unpack what this study found, in clear terms for beginners, with practical takeaways and thoughtful questions at the end.
Overview
Diabetes that exists before pregnancy and gestational diabetes mellitus (GDM) diagnosed during pregnancy are both concerns for maternal and fetal health. In Thailand, the burden of diabetes has been increasing, with more than 6.5 million people affected in 2024. At Bhumibol Adulyajej Hospital (BAH), the rate of diabetes in pregnancy was 24.7% in 2024.
Diabetes in pregnancy is linked to several adverse outcomes for mother and baby, including pregnancy-induced hypertension, preterm birth, neonatal hyperbilirubinemia, and babies who are large for gestational age. It’s also associated with fetal heart problems, such as structural heart defects and impaired function. Maternal high blood sugar elevates fetal insulin levels, and insulin can promote heart muscle growth, leading to thicker heart walls. Fetal echocardiography can help detect these changes early. Severe fetal cardiac hypertrophy has been identified as a significant risk factor for stillbirth or in-utero heart failure, and poorly controlled diabetes can worsen neonatal outcomes like NICU admission, stillbirth, and neonatal death.
Traditionally, clinicians measure the thickness of the heart’s interventricular septum (IVS) with 2D ultrasound or M-mode. These methods, however, may miss mild hypertrophy. Four-dimensional (4D) ultrasound, which uses spatiotemporal image correlation (STIC) and the VOCAL analysis method, can delineate the edges of the ventricular walls more precisely. This improves accuracy in measuring the IVS and allows earlier detection of fetal hypertrophy.
Purpose
This study aimed to compare fetal IVS volumes between fetuses of women with GDM and those of healthy pregnant women using 4D ultrasound with STIC and VOCAL. It also examined whether abnormal IVS volume correlates with adverse pregnancy outcomes.
Methods
- Design: Prospective cross-sectional study approved by the BAIRB (IRB 62/67) and registered as TCTR20241016006. Informed consent was obtained from all participants.
- Setting and participants: Singleton pregnancies between 29 and 34 weeks’ gestation were recruited from the antenatal clinic at BAH between November 2024 and March 2025. Participants were divided into GDM and healthy groups.
- Inclusion criteria: Singleton pregnancies, GA 29–34 weeks, delivery at BAH.
- Exclusion criteria: Fetuses with other cardiac anomalies or chromosomal abnormalities; overt or pre-existing maternal diabetes.
- Diagnostics: All participants underwent universal diabetes screening. Overt or pregestational diabetes was excluded. GDM was diagnosed by a 75-g oral glucose tolerance test (OGTT) with thresholds: fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥153 mg/dL.
- Imaging: Fetal echocardiography used Voluson E8/E10 systems with 3D/4D volumes obtained in three attempts and analyzed offline. The IVS was measured at diastole in the widest ventricular phase using the VOCAL method with six rotational steps, yielding a three-dimensional IVS volume.
- Reliability: Intra- and inter-operator consistency were strong, with intraclass correlation coefficients around 0.97–0.98.
- Outcomes: Primary outcome was fetal IVS volume; secondary outcomes included adverse neonatal events (e.g., hyperbilirubinemia, respiratory distress, NICU admission, preterm birth, Apgar scores, stillbirth, PIH).
- Statistics: Comparisons used t-tests and chi-square tests; ANCOVA adjusted for age and BMI where relevant. A p-value < 0.05 indicated significance.
Results
- Participants: 111 singleton pregnancies—63 with GDM and 48 healthy controls.
- Baseline differences: The GDM group was older (mean age 33.0 vs 27.9 years) and had higher BMI (31.1 vs 26.8 kg/m²).
- IVS volume: Mean fetal IVS volume was higher in the GDM group (347.1 mm³) than in controls (221.5 mm³). After adjusting for age and BMI, the IVS volume remained significantly higher in the GDM group (p = 0.003).
- Neonatal outcomes: Adverse neonatal outcomes (preterm birth, RDS, hyperbilirubinemia, PIH, NICU admission) were similar between groups. There were no cases of low Apgar scores or stillbirths, and only one forceps-related facial mark occurred in the healthy group.
- Predictive value: An IVS volume cutoff of 419.8 mm³ predicted hyperbilirubinemia (HBB) and respiratory distress syndrome (RDS) with sensitivities around 55–56% and negative predictive values (NPV) of 94.0% for HBB and 95.2% for RDS. Positive predictive values (PPV) were low (around 17–21%).
Interpretation
- Key finding: In pregnancies affected by GDM, fetal IVS volume was larger than in healthy pregnancies, even after accounting for age and BMI. This supports the idea that fetal cardiac hypertrophy is more common with maternal diabetes and can be detected with 4D ultrasound.
- Clinical utility: A high NPV means that a IVS volume below 419.8 mm³ strongly suggests a low risk of the baby developing HBB or RDS in the near term, which can reassure families and guide follow-up care. The low PPV indicates that an IVS volume above the cutoff does not reliably confirm these conditions, so it should trigger closer monitoring rather than definitive diagnosis.
- Practical takeaway: Measuring fetal IVS volume could be considered in the third trimester for pregnancies complicated by GDM (29–34 weeks) to stratify risk and inform surveillance, recognizing that this tool has limited sensitivity and specificity and should be integrated with other clinical information.
Limitations and considerations
- A notable portion of healthy participants delivered at other facilities, which could affect follow-up data.
- The identical 419.8 mm³ cutoff for predicting both HBB and RDS may reflect overfitting or ROC selection bias; larger future studies are needed to refine thresholds.
- The study’s population had higher maternal age and BMI in the GDM group, though adjustments were made in analysis.
Conclusions
Fetal IVS volume measured in the early third trimester is higher in pregnancies affected by GDM compared with healthy pregnancies. A cutoff of 419.8 mm³ predicted HBB and RDS with high negative predictive value (94.0% for HBB and 95.2% for RDS), suggesting that IVS volume measurement could be a useful part of risk assessment in GDM pregnancies. However, due to modest sensitivity and very low positive predictive values, IVS volume should be used as a supplementary tool to identify low-risk cases and to prompt closer monitoring when volumes exceed the threshold. Routine IVS volume assessment in GDM pregnancies during 29–34 weeks could help identify low-risk babies and flag those needing closer observation and potential early intervention.
Data sharing
Data are available on request from the corresponding author and are not publicly available due to privacy and ethical restrictions.
Ethics and funding
The study was approved by BAIRB (62/67) and conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all participants. Funding was provided by the Bhumibol Adulyadej Hospital research fund. The authors report no conflicts of interest.
Thought-provoking closing
Could fetal IVS volume measurement become a mainstream screen in GDM pregnancies, or will its limitations keep it as an adjunct rather than a standard test? Share your thoughts in the comments: Do you see this technique as a valuable early warning system or as an imperfect predictor that should not change management?
