In recent decades, maternal–fetal medicine has undergone substantial advancements in the management of high-risk pregnancies. These include enhanced prenatal screening and diagnosis facilitated by innovations in ultrasound imaging, as well as the advances in fetal medical and interventional therapies informed by the deeper understanding of pathophysiological mechanisms underlying fetal and maternal disease processes. Collectively, these have contributed to measurable reductions in maternal and perinatal morbidity and mortality [1]. However, the identification of certain fetal conditions using ultrasound remains challenging because of suboptimal acoustic windows, fetal positioning, maternal body habitus, and limited soft tissue contrast [2]. These challenges can delay diagnosis and management, and potentially impact the timing of interventions, as well as the quality of prenatal counseling regarding the child's future health, development, and quality of life.

Recent advances in fetal magnetic resonance imaging (MRI) have emerged as a feasible alternative when ultrasound findings are inconclusive or limited. Fetal MRI offers superior soft tissue contrast which can enhance the characterization of complex fetal conditions. This was facilitated by the development of accelerated image acquisition techniques and motion-correction algorithms to reduce maternal breathing and fetal movement artifacts, thereby reducing scan times and improving the overall image quality [3]. Therefore, fetal MRI could serve as a valuable adjunct to clinical assessment, optimizing prenatal management and facilitating targeted interventions in high-risk pregnancies.

This special issue explores the expanding role of fetal MRI in the diagnosis, prognosis, and planning of interventions in complex fetal conditions in high-risk pregnancies.

Fetal MRI offers enhanced anatomical resolution and tissue characterization of the developing fetal brain [4]. Ren et al. provided a comprehensive review on the utility of fetal MRI on the diagnosis of congenital brain tumors including teratomas, astrocytomas, and choroid plexus tumors [5]. Key findings include superior tissue contrast to characterize tumor morphology, volume, and mass effect, which may prompt additional investigations for associated pathologies, guide the timing of delivery for postnatal interventions, and aid prenatal counseling [6]. Liu and Xiao presented a rare case of fetal periventricular nodular heterotopia identified by fetal MRI after ultrasound detection of a posterior fossa cyst [7]. Fetal MRI detected a gray matter nodule in the right lateral ventricular wall leading to suspicion of fetal gray matter heterotopia, which was confirmed by brain MRI at 7 months of age with no associated abnormal neurological presentation. Although a neuronal migration disorder, these findings highlight some individuals may not develop neurological issues in early life. Further characterization including the presence of additional brain malformations and genetic testing is likely to improve the prognosis and prenatal counseling of the child's future neurodevelopmental outcomes [8]. Lastly, Shan et al. provided normative reference values for a broad range of cerebral metabolites using fetal magnetic resonance spectroscopy including glutamate, glutamine, N-acetylaspartate, N-acetylaspartylglutamate, choline, phosphocreatine, myo-inositol [9]. Changes of these cerebral metabolites, measured from mid-gestation to term, were found to correlate with gestational age. Profiling fetal cerebral metabolites may aid in assessing the risk of impared brain development and maturation, with potential implications for predicting early neurodevelopmental outcomes, as previously demonstrated in fetuses with congenital heart disease [10].

Beyond the fetal brain, fetal MRI serves an important adjunct role in evaluating anomalies in other fetal organ systems. Yan et al. report a complex case of congenital tracheal stenosis with associated tracheoesophageal fistula, duodenal atresia, and polydactyly confirmed by fetal MRI [11]. The authors emphasize the utility of fetal MRI in confirming the diagnosis of congenital tracheal stenosis, which can aid in timely referral to a tertiary care center for perinatal multidisciplinary management. Zheng et al. investigated myocardial alterations in fetuses with congenital heart disease using post-mortem myocardial MRI [12]. T2 relaxation times were significantly elevated in cyanotic congenital heart disease compared to controls, suggesting subclinical myocardial injury. These findings demonstrate the potential utility of myocardial T2 mapping in fetal cardiac MRI as a novel biomarker for fetal cardiac compromise, as previous studies have also demonstrated diminished combined ventricular output in the setting of cyanotic congenital heart disease is associated with early mortality [13]. Yang et al. analyzed prenatal imaging features by ultrasound and fetal MRI with postnatal outcomes in patients diagnosed with congenital hepatic hemangiomas [14]. Overall, larger tumors (≥ 4 cm) were associated with mixed echogenicity and a higher risk of complications. Notably, a previously undescribed proliferative-regressive growth pattern was identified. These findings provide additional information to the characteristics and disease progression of congenital hepatic hemangiomas.

Fetal MRI is increasingly integrated into the preoperative planning of in utero surgical procedures. Bian et al. provide a comprehensive review of the role of MRI in guiding ex utero intrapartum treatment procedures, open fetal surgery, fetoscopic interventions, and percutaneous techniques [15]. Fetal MRI allows for precise anatomical mapping of lesions and their relationship to adjacent structures, facilitating risk assessment and individualized surgical planning. During early pregnancy, MRI may also play an important role in diagnosing atypical presentations of placental implantation abnormalities. Song and Li report a case of retroperitoneal ectopic pregnancy, which was initially suspected as a molar pregnancy based on ultrasound finding [16]; however, human chorionic gonadotropin remained elevated following uterine evacuation. Further investigation using fetal MRI revealed a cystic mass to the anterior sacral region, and the diagnosis of ectopic pregnancy was confirmed by surgical resection. This case illustrates the utility of MRI in clarifying atypical presentations when initial investigations are inconclusive or when there is incomplete clinical resolution.

As fetal MRI technology continues to advance, its potential to improve the diagnosis and prognostication of complex fetal conditions is increasingly evident. Beyond high-resolution anatomical imaging, the integration of functional imaging, such as fetal 4-dimensional flow MRI, offers the opportunity to assess fetal hemodynamics in greater detail [17]. These methods may provide valuable insights to the consequences of circulatory disturbances on perinatal outcomes. Moreover, the growing application of artificial intelligence in prenatal imaging in gaining momentum [18]. Automated segmentation and pattern recognition algorithms holds promise to streamline image analysis, reduce interobserver variability, and support the development of predictive risk-stratification models. Ultimately, these innovations may help guide clinical decision-making and contribute to the improvement of maternal–fetal outcomes.

Author Contributions

Su-Zhen Dong: conceptualization (lead), writing – original draft preparation (lead), writing – review and editing (lead). Fu-Tsuen Lee: conceptualization (support), writing – original draft preparation (support), writing – review and editing (support). Lianxiang Xiao: conceptualization (lead), writing – original draft preparation (lead), writing – review and editing (lead), supervision (equal). Liqun Sun: conceptualization (lead), writing – original draft preparation (lead), writing – review and editing (lead), supervision (lead).

Ethics Statement

The authors have nothing to report.

Consent

The authors have nothing to report.

Conflicts of Interest

This article belongs to a special issue (SI)-Fetal Imaging, Maternal and Children Imaging. As the SI's Guest Editors, Professors Su-Zhen Dong, Lianxiang Xiao and Liqun Sun are excluded from all the editorial decision related to the publication of this article. The remaining author declares no conflicts of interest.