A retrospective study in a special case context: vasa praevia due to a velamentous umbilical cord insertion

Introduction

Velamentous cord insertion was first described in the medical literature by Friedrich Wilhelm Lell in 1907, being known and described as a condition in which the umbilical cord inserts into the amniotic membrane near the placental margin, rather than attaching directly to the placenta. This insertion can lead to the formation of fragile blood vessels that extend from the cord to the placenta, covered only by the amnion. The situation becomes more serious when these vessels tend to insert near or over the internal cervical os, thus associating velamentous insertion with vasa praevia^(1,2).

The etiology of this pathology is complex and not fully understood, primarily because it is a relatively rare condition. The main risk factors listed by authors include twin gestation, pregnancies conceived through assisted reproductive technology, while bleeding during pregnancy, advanced maternal age, multiparity, female fetus, and previous pregnancy with abnormal cord insertion were other risk factors^(3-5).

Additional risk factors predisposing to this umbilical cord anomaly, as documented in medical literature and studies conducted on different cohorts of pregnant women worldwide, include the following:

• Genetic factors. Certain genetic anomalies can influence how the umbilical cord develops and attaches to the placenta and uterus. For example, genetic mutations can affect placental vascular formation or predispose to umbilical cord anomalies^(6,7).
• Placental factors. Placental anomalies, such as malposition or abnormal placental shape, can play a role in the occurrence of velamentous cord insertion. These anomalies can affect how the umbilical cord attaches to the placenta or disrupt the development of placental vascularization^(8,9).
• Environmental factors. Exposure to certain harmful environmental factors during pregnancy, such as smoking, alcohol consumption, or exposure to toxins, can increase the risk of umbilical cord anomalies, including velamentous insertion. These substances can affect placental development and umbilical cord formation.
• Factors related to fetal development. Anomalies in fetal development, such as disorders in the formation of blood vessels around the umbilical cord, can contribute to velamentous insertion. Factors such as deficiencies in angiogenesis or vascular development can influence how the umbilical cord forms and attaches^(10,11).
• Complex interactions between the above factors. In many cases, velamentous cord insertion results from the interaction of multiple genetic, placental, environmental, and fetal development factors.

Vasa praevia is a rare pathology of the fetal appendages, characterized by the umbilical-placental vessels passing through the chorioamniotic membranes near or over the internal cervical os, without being protected by the Wharton’s jelly. This condition is detected in approximately 1 in 1200 to 1 in 2500 births, with 15-30% of cases being discovered in the second trimester of pregnancy, and its incidence is on the rise⁽¹²⁾.

Depending on the insertion of the vessels, there are two types of vasa praevia:

• Type 1 (25-62%) represents the passage of placental vessels over the internal os to reach the placental margin (velamentous insertion).
• Type 2 (33-75%) results from the presence of an accessory lobe of the placenta, such as bilobate placenta, where unprotected vessels cross over the internal os⁽¹²⁾.

Some articles have discussed the necessity of introducing a third type of vasa praevia, which is more commonly associated with the insertion of umbilical-placental veins that form anastomoses with different parts of the placenta and are inserted low^(13,14).

Approximately 2% of velamentous insertions are associated with vasa praevia⁽¹⁵⁾.

Dr. William Hunter first described vasa praevia in 1774, but the ultrasound description was only performed in 1987 by Gianopoulos. In 1990, Nelson described vasa praevia using transvaginal examination with Doppler effect, having a sensitivity and specificity of 100% and 99%, respectively⁽¹⁾. Thanks to this diagnostic tool, the risk of accidentally detecting vascular pathology during labor is reduced, which is extremely important, because vasa praevia has severe consequences for both the mother and the fetus^(16,17).

In some articles, three theories are identified that might explain the occurrence of umbilical anomalies such as vasa praevia and velamentous cord insertion:

• The “polarity theory”, which may arise when the embryo does not face the implantation base, and the umbilical vessels extend between the umbilical cord insertion and the placenta at the implantation base.
• The “trophotropism theory”, which explains these pathologies as low-placenta pathologies. This situation occurs when an early placenta migrates with advancing gestational age to ensure better blood supply and proper development, resulting in either marginal or membranous insertion⁽¹⁸⁾.
• The “abnormal placental development theory due to decreased chorionic vessel branching”, which suggests that off-center insertion results from abnormal vasculogenesis in the placenta.

The role of multiple pregnancies as a risk factor for these pathologies remains unclear, as some studies include it as a risk factor while others do not. Nevertheless, the frequency of vasa praevia is highly dependent on whether the placentation in multiple pregnancies is monochorionic or dichorionic, with the former having a higher incidence of vasa praevia.

We present a retrospective study conducted at the Co­unty Emergency Clinical Hospital in Constanţa, Romania, over a period of five years (2019-2023), which included a total of 14,166 births, among which seven cases were associated with velamentous insertion of the umbilical cord. In this retrospective study, we calculated the incidence of the velamentous cord insertion (it was 0.05%), and we included a case study to explore in detail the clinical manifestations and management of a specific case of velamentous insertion of the umbilical cord associated with vasa praevia.

Case presentation

We present the case of a 44-year-old patient who presented to the gynecology emergency department with spontaneous vaginal bleeding. The decision was made to admit the patient with the diagnosis of IIIG IIP pregnancy at 38/39 weeks, live single fetus, vertex presentation, painful uterine contractions.

The patient had no known associated pathologies. Her first delivery was at term, without obstetric complications during pregnancy or postnatally. At the time of presentation, the bleeding was reduced and did not present as a major obstetric emergency. The baby had a good biophysical profile, with normal uterine tone and no uterine contractions. Therefore, the decision was made to admit the patient to the maternity ward for appropriate monitoring and investigation, as the patient did not have regular obstetric checkups, either through a family doctor or otherwise, due to her low socioeconomic status and rural background. Despite this, the uterine bleeding led the patient to a high-level medical center.

During the day of admission, the patient’s condition was stable, with brownish discharge without other clinical signs. In the next 12 hours, after a shift change, the patient exhibited moderate spontaneous bleeding with clots, but no other clinical signs. A reevaluation by ultrasound revealed the presence of several fetal vessels inserting at the internal cervical os, originating from the lower placental pole (Figure 1). Given that vaginal bleeding and fetal bradycardia began to develop, an emergency surgical intervention was decided.
 

After fetal extraction, it was found that the placenta, inserted on the posterior uterine wall, had velamentous insertion of the umbilical cord with early placental abruption (Figures 2 and 3). Both fetal and maternal postnatal progress was favorable, although a prolonged hospitalization was needed for fetal stabilization. The obstetrical outcome was successful, and we are proud to have saved two lives, given that in such clinical-obstetrical situations, success is not always achieved, because of the severe pathological effects associated with placental abruption or vasa praevia, especially when these pathologies are present together.
 

Discussion

This umbilical-placental pathology is quite rare. According to Williams Obstetrics, the incidence is around 1%, though some sources report an incidence of up to 2.5%. However, in some studies conducted on large population samples, such incidence has been observed⁽¹⁹⁾. For example, in a study conducted by Räisänen et al. (2012) in Finland, between 2000 and 2011, on a cohort of 26,849 singleton pregnancies, the incidence of velamentous cord insertion was found to be 2.4%, with 633 cases out of 26,849⁽²⁰⁾.

In another study, on a smaller population group, a similar incidence was observed, but it was noted that assisted reproductive techniques predispose to a higher incidence. In a study conducted in Japan, in 2021, on a cohort of 906 births, where pregnancies were achieved through assisted reproductive technology, the authors, Furuya, Kubonoya and Yamaguchi (2021), reported that 55 out of 906 cases had velamentous cord insertion, resulting in an incidence of 6.1%^(21-23).

Another study, conducted in South Korea, in 2021, Lee et al. (2021), on a cohort of 941 twin pregnancies, found that velamentous cord insertion was more common in dichorionic twin pregnancies (7.8%) compared to monochorionic placentation (5.8%)^(24-27).

Interestingly, the incidence of vasa praevia associated with velamentous cord insertion increases in cases where low placental development occurs. These data are evident in a 2010 article analyzing ultrasound examinations in vasa praevia, where 90% of vasa praevia cases were associated with velamentous insertion, compared to 1.6% in the control group⁽²⁸⁾.

It is essential to understand that, despite medical research advancements, the exact cause of velamentous cord insertion often remains unknown, and this pathology may be discovered during pregnancy monitoring or childbirth^(29-31).

As an example, in an Australian study conducted in 2017 by. Sullivan et al., 63 cases of vasa praevia were identified, of which 58 cases were detected during pregnancy. Out of these, 55 out of 58 vasa praevia cases were associated with velamentous cord insertion. In four out of five patients where these pathologies were not detected prenatally, emergency surgery was performed because of life-threatening situations, resulting in a 40% fetal prenatal mortality rate, with one vaginal birth due to antenatal fetal death. Additionally, 68% of births were premature, and 29% were associated with low birth weight⁽³²⁾.

Similarly, reviewing a meta-analysis conducted by Siargkas et al. in 2022, on 11 patients, of which four cases of velamentous insertion were discovered during pregnancy and seven postnatally, the authors found that the prevalence of velamentous insertion was 1.4% in singleton pregnancies. Compared to the control group with central and paracentral insertion, the presence of velamentous cord insertion was associated with a higher incidence of pathologies such as low birth weight, hypertension, preeclampsia, placental abruption, intrauterine fetal death, preterm birth, emergency surgical intervention, low Apgar scores, and admission to neonatal intensive care⁽³³⁾.

In a retrospective analysis conducted in 2020 by Yang et al., on 501 cases of velamentous cord insertion out of 59,976 births, over the period 2004-2014, the prevalence was found to be 0.84%. The colleagues observed that risk factors and various pathological aspects were linked to fetal deaths, preterm birth, low birth weight, and low Apgar scores⁽³⁴⁾.

All these articles demonstrate that, although these umbilical-placental pathologies have a low population incidence, they have devastating maternal-fetal consequences. Therefore, it is crucial for every pregnant woman to undergo routine pregnancy ultrasound and, especially, fetal morphology scans, which are crucial moments for the timely detection of possible umbilical anomalies or pathological placental insertion. Otherwise, spontaneous detection of these anomalies during an emergency situation is associated with a very high rate of fetal death, significant neurological conditions for the fetus due to major fetal hemorrhages, and both fetal and maternal deaths, with lifelong repercussions^(35-37).

The anatomical-pathological aspect of placentas and of the placental vessels is extremely important to analyze in these cases, when the placental vascular appearance can be modified compared to normal⁽³⁸⁾.

A cohort study conducted in 2023 by Zhang et al. reported that, out of 2,278,561 pregnancies, there were 1320 pregnancies with vasa praevia. The weighted grouped incidence of vasa praevia was 0.79 (95% CI; 0.59 to 1.01) per 1000 examined pregnancies, which corresponded to an incidence of one case of vasa praevia in 1271 pregnancies (95% CI; 990 to 1692)⁽³⁹⁾.

The guidelines of the Society for Maternal-Fetal Medicine (SMFM) published in 2015 state that “there are no standardized criteria for how close the vessels connecting the umbilicus to the placental disc must be to the internal os to constitute vasa praevia”⁽¹⁾. Some authors consider it to be vasa praevia when the vessels are within 2 cm of the internal os; however, it is difficult to define this clinical situation as a standard because, regardless of the distance of the vessels from the internal os, the dilation of the cervical canal that occurs during labor can lead to the rupture of pathologically inserted vessels, which is associated with catastrophic bleeding, especially for the fetus, given that the fetal circulatory blood volume is approximately 300 ml.

A large international multicenter cohort study of 155 cases found that, when vasa praevia was not diagnosed prenatally, there was a perinatal mortality rate of 56%⁽⁴⁰⁾.

The risks of perinatal death and hypoxic morbidity were 25 times and 50 times higher, respectively, in those not diagnosed prenatally compared to those diagnosed prenatally⁽⁴¹⁾.

Similarly, maternal risks are primarily associated with continuous hospitalizations due to recurring uterine bleeding throughout pregnancy, especially when vasa praevia is associated with abnormal placentation, leading to maternal anxiety and socioeconomic consequences.

The most common of these include preterm birth, with its consequences on the fetal organism, chronic and acute fetal distress, having prenatal and postnatal effects, and in the most difficult situations, being associated with a high rate of fetal death^(42-44).

Maternal hemorrhages lead to the weakening of the body, predisposing it to chronic anemia, which in turn increases susceptibility to infections. In severe situations, maternal shock with tubular renal necrosis, disseminated intravascular coagulation, and prolonged hospitalizations, with their psychological consequences, may occur^(42,45).

The symptomatology in these cases can be complex. Sometimes it can be represented by pain in the uterus or in one of the flanks, manifestations that can be included as a differential diagnosis with cases of ovarian tumors (tubo-ovarian cysts or abscesses)⁽⁴⁶⁾ or with placental abruption, especially when vaginal bleeding is present⁽⁴⁷⁾.

It is extremely important to understand that many pathological consequences due to the presence of this anomaly in fetal appendages can be prevented if umbilical-placental pathologies are detected early during periodic ultrasound examinations, with a significant emphasis on performing fetal morphology scans and the attentiveness of the operator conducting these ultrasound examinations^(42,48).

We must alert readers that, due to the presence of paternal Rh incompatibility, it is crucial to prevent potential immune sensitization by applying the SOGR protocol, including both prophylactic and therapeutic anti-Rh vaccinations. The presence or absence of anti-D antibodies is of great importance here. Additionally, maternal-fetal bleeding can predispose to chronic fetal anemia⁽⁴⁹⁾.

A useful tool in this context can be the maximum velocity on the middle cerebral artery; if it exceeds 1.5 MoM, and if the clinical situation warrants, cordocentesis can be performed to determine fetal hemoglobin and hematocrit levels.

As risk factors for developing umbilical and placental vascular anomalies, some authors describe assisted reproductive technologies. For example, a study by Matsuzaki et al. (2022) found that the prevalence of vasa praevia appears to be higher (approximately 0.3-0.5%) in women who have undergone assisted reproductive technologies⁽⁵⁰⁾.

Conclusions

Imaging examinations, especially the second-trimester morphological ultrasound, should be routinely performed on all pregnant women. In the case of unmonitored patients who have not benefited from a second-trimester pregnancy ultrasound and have not been monitored by ultrasound during pregnancy, a careful ultrasound examination of the placental surface and the insertion of the umbilical cord is necessary, even during labor.

Vaginal bleeding in a pregnant patient should also raise the suspicion of an umbilical cord insertion anomaly.

Acknowledgments: No acknowledgments.

Data availability statement: The data supporting this study’s findings are available on request from the corresponding author, Lucian Şerbănescu.

Autori pentru corespondenţă: Lucian Şerbănescu E-mail: lucian.serbanescu@365.univ-ovidius.ro

CONFLICT OF INTEREST: none declared.

FINANCIAL SUPPORT: none declared.

This work is permanently accessible online free of charge and published under the CC-BY.