Prenatal diagnosis of total vasa previa using 2D and HD live flow combined with spatiotemporal correlation: a case series description

Introduction

Vasa previa (VP), a rare obstetric condition, is characterized by fetal blood vessels traversing the fetal membranes, situated below the presenting part, and overlaying or intersecting the endocervical os (1,2). These vessels, unprotected by Wharton’s jelly or placental tissue, are at an increased risk of compression and rupture during labor, potentially leading to fetal distress, hemorrhagic shock, and neonatal mortality (3). Prenatal ultrasonography serves as the cornerstone for diagnosing VP. Spatiotemporal image correlation (STIC) has significantly improved the diagnostic precision of VP by offering three-dimensional (3D) visualization of the anterior vessels, thereby bolstering diagnostic confidence. The precise mapping of the aberrant vessels provided by this technology is instrumental for subsequent clinical interventions.

VP is categorized into three types (3): Type I, featuring a single lobe placenta, often referred to as a velamentous placenta; Type II, involving multilobed placentas such as a succenturiate lobe or a bilobed placenta; and Type III, characterized by vessels that run in a boomerang shape, originating from and inserting back into the placental edge (4).

Case presentation

This study includes four cases of VP diagnosed prenatally via ultrasound at the Gansu Provincial Maternity and Child-care Hospital between May 2018 and March 2022. The cohort consisted of women aged 28–36 years, with a median age of 32 years. The gestational age at the time of examination ranged from 21 to 25 weeks, with a median of 23.5 weeks. All cases were singleton pregnancies resulting from natural conception. The distribution of VP types was three Type I and one Type II. Case 1, 2, and 3 were characterized by a velamentous placenta (Figure 1A,1B). Case 4 was distinguished by a bilobed placenta. All four cases were identified during the mid-gestational period with suspected VP at the internal cervical os, and subsequently imaged using STIC technology. None of the women had pregnancy-related comorbidities. Each underwent cesarean section in late pregnancy.

Figure 1 Prenatal ultrasound imaging. (A) A case of type I (case 1, velamentous placenta). The two-dimensional sonogram shows VP at the level of the internal cervical os, with spectral Doppler indicating the VP waveform as venous, which does not change with respiratory movements. (B) In the same patient (case 1), the VP at the cervical internal os is shown, with spectral Doppler demonstrating the vasa previa waveform as arterial, corresponding to the fetal heart rate. (C,D) STIC imaging displays the vasa previa from case 2 and case 3 (indicated by white arrows). VP, vasa previa; STIC, spatiotemporal image correlation.

All procedures performed in this study were in accordance with the ethical standards of the Medical Ethics Committee of Gansu Provincial Maternity and Child-care Hospital and with the Helsinki Declaration (as revised in 2013). Written informed consent was provided by the patients or their next of kin for publication of this article and any accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

The incidence of VP is estimated to be between 0.02% to 0.06% in the literature (5). Despite its rarity, the rupture of VP during labor poses a significant obstetric emergency, with reported fetal mortality rates as high as 44% (6). However, accurate prenatal diagnosis via ultrasound can increase the fetal survival rate to 97–100% (7).

The etiology of VP is linked to several risk factors, including multiple pregnancies, the presence of a lobulated or a low-lying placenta, and the utilization of assisted reproductive technologies (8). In clinical practice, women presenting with these risk factors should undergo an initial assessment for abnormal umbilical cord insertion to rule out sail-shaped and racket placentas. Subsequently, placental morphology and multiplicity should be examined to exclude the presence of multilobed or parietal placentas. Finally, during the diagnosis of placenta previa, meticulous observation of the placental margin membranes for blood vessels is crucial to exclude Type III VP. The second trimester, with moderate amniotic fluid volume and increased fetal mobility, provides an optimal window for detailed placental evaluation. In late pregnancy, visualization of the endocervical os can be challenging due to advanced fetal descent, necessitating transvaginal screening when transabdominal ultrasound is inconclusive.

In 2D ultrasound, the endocervical os may exhibit a “line” or “bubble” sign in cases of VP. However, it is essential to differentiate these from varicose uterine vessels, amniotic bands, and placental marginal venous sinuses, which may also manifest in the same region. Color and spectral Doppler imaging can aid in discerning these structures (Figure 1C). A spectral waveform consistent with the maternal heart rate precludes a diagnosis of VP. The spectral characteristics of the fetal and maternal veins do not differ significantly; however, the vein can be identified as fetal by tracing it to the placenta or as maternal by observing the mother’s respiratory movements. It is imperative to distinguish vascular structures pulsating with the fetal heart rate from conditions such as umbilical cord preexposure or prolapse (Figure 1B). In cases of umbilical cord preexposure, the presence of a helical structure and irregular cord positioning rules out VP. Encouraging the mother to change positions and observing any shifts in the umbilical cord vessel positions can be diagnostically informative.

When the anterior vessel crosses the endocervical os, the sagittal view might inadvertently capture a transverse vessel view, predisposing to a missed diagnosis. To prevent misdiagnosis or oversight of the VP, a longitudinal and transverse fan scan should be conducted to ascertain the relationship between the suspected vessel and the endocervical os.

The diagnosis of VP primarily relies on 2D ultrasound and color Doppler imaging, yet the latter can be prone to flow spillage and may not be sensitive to small, low-velocity flows. The STIC combined with high-definition flow imaging (HD live flow), offers an angle-independent, enhanced sensitivity to blood flow, which is particularly beneficial for visualizing small vessels. This approach allows for precise observation of the umbilical vessels’ location and their relationship with the placenta. STIC provides 3D spatial visualization of the placenta, umbilical cord, and vessels (Figure 1C,1D), along with the direction of umbilical vasculature, in an intuitive manner. This technology can significantly bolster diagnostic confidence for vascular pregnancies. When the presence of VP is suspected, the use of STIC technology can assist in reaching a definitive diagnosis in a more intuitive manner. For observers with less diagnostic experience, the 3D display of the VP trajectory can help to reveal details that may be easily overlooked in 2D ultrasound. However, employing this technology for imaging may introduce additional noise into the images, which can hinder the differentiation between umbilical and uterine vessels. As per the latest international guidelines, pregnant women diagnosed with VP should be hospitalized for elective cesarean section between 34 and 36 weeks of gestation (7-9). The STIC technique, by directly illustrating the spatial alignment of the anterior vessels, can assist operators in avoiding fetal vessel laceration (Figure 2). Consequently, as a valuable adjunct to 2D color Doppler flow imaging (2D-CDFI), STIC can serve as an effective supplementary method for prenatal VP diagnosis.

Figure 2 Postoperative placental specimen from a patient with a velamentous placenta and type I (case 1). The umbilical cord insertion site is located at the edge of the placenta (indicated by white arrow). The fetal membranes show branches of the umbilical vessels running without Wharton’s jelly (marked with *).

Acknowledgments

Funding: This work was supported by the Natural Science Foundation of Gansu Province (No. 23JRRA1391) and the Gansu Health Industry Scientific Research Program (No. GSWSQN2021-006).

Footnote

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-1226/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the Medical Ethics Committee of Gansu Provincial Maternity and Child-care Hospital and with the Helsinki Declaration (as revised in 2013). Written informed consent was provided by the patients or their next of kin for publication of this article and any accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Sinkey RG, Odibo AO, Dashe JS. #37: Diagnosis and management of vasa previa. Am J Obstet Gynecol 2015;213:615-9. [Crossref] [PubMed]
2. Jain V, Gagnon R. Guideline No. 439: Diagnosis and Management of Vasa Previa. J Obstet Gynaecol Can 2023;45:506-18. [Crossref] [PubMed]
3. Ranzini AC, Oyelese Y. How to screen for vasa previa. Ultrasound Obstet Gynecol 2021;57:720-5. [Crossref] [PubMed]
4. Suekane T, Tachibana D, Pooh RK, Misugi T, Koyama M. Type-3 vasa previa: normal umbilical cord insertion cannot exclude vasa previa in cases with abnormal placental location. Ultrasound Obstet Gynecol 2020;55:556-7. [Crossref] [PubMed]
5. Ruiter L, Kok N, Limpens J, Derks JB, de Graaf IM, Mol B, Pajkrt E. Incidence of and risk indicators for vasa praevia: a systematic review. BJOG 2016;123:1278-87. [Crossref] [PubMed]
6. Oyelese Y, Catanzarite V, Prefumo F, Lashley S, Schachter M, Tovbin Y, Goldstein V, Smulian JC. Vasa previa: the impact of prenatal diagnosis on outcomes. Obstet Gynecol 2004;103:937-42. [Crossref] [PubMed]
7. Zhang W, Geris S, Al-Emara N, Ramadan G, Sotiriadis A, Akolekar R. Perinatal outcome of pregnancies with prenatal diagnosis of vasa previa: systematic review and meta-analysis. Ultrasound Obstet Gynecol 2021;57:710-9. [Crossref] [PubMed]
8. Yerlikaya-Schatten G, Chalubinski KM, Pils S, Springer S, Ott J. Risk-adapted management for vasa praevia: a retrospective study about individualized timing of caesarean section. Arch Gynecol Obstet 2019;299:1545-50. [Crossref] [PubMed]
9. Gyamfi-Bannerman C. Society for Maternal-Fetal Medicine (SMFM) Consult Series #44: Management of bleeding in the late preterm period. Am J Obstet Gynecol 2018;218:B2-8. [Crossref] [PubMed]