Hypoplastic umbilical artery is accepted as an incomplete form of SUA (
4). Although its etiology is unknown, this condition has been found to be associated with various pathologies, such as trisomy 18, polyhydramnios, congenital heart disease, IUGR, placental infarction, umbilical cord hematoma, and abnormal umbilical cord insertion ( 5- 7). Dolkart et al. studied umbilical artery diameters and found a 2 mm difference in six cases measured in the second and third trimesters. One of these six cases was accompanied by preterm birth, and another resulted in death due to neonatal liver failure three months after birth. No clinical pathology was reported in the other four cases ( 9). In another study by Predanic et al., no pathological findings were detected during the examination of the placental and umbilical cords of 12 pregnancies demonstrating significant discordance (> 29.5%, or the 95th percentile) between the two umbilical artery diameters ( 2). Conversely, Raio et al. demonstrated abnormal cord insertions (marginal, velamentous, and eccentric) in eight of 14 cases with > 1 mm differences between the umbilical artery diameters. Placental abnormalities were detected in the remaining seven cases (three placental infarctions, two bipartite placentas, one placenta succenturiata, one chorangioma, and one absence of Hyrtl anastomosis) ( 7).
Petrikovsky and Schneider detected hypoplastic umbilical arteries using prenatal US in 12 patients. They found one of these cases to be associated with trisomy 18, three with polyhydramnios, one with congenital heart disease, and two with IUGR. They also found maternal diabetes in four cases (
4). In our study, no placental, umbilical cord, or fetal pathologies were detected in the patients with hypoplastic umbilical arteries. However, two pregnancies were complicated by polyhydramnios, four by meconium staining, and one by gestational diabetes.
Sepulveda et al. examined blood-flow patterns in the CIA in 15 cases of SUA. They found that PI values on the side not attending to fetoplacental circulation were higher than on the contralateral side (
8). In our study, the hypoplastic umbilical artery group demonstrated higher PI and RI values for the non-dominant CIAs in comparison with the dominant side during the second trimester. The higher RI values may have been due to the smaller diameter of the CIA on the side of the hypoplastic umbilical artery at early gestational stages.
In a study of eight cases of SUA from birth to 4 years of age, Meyer et al. reported significant anatomical and histological differences between the CIAs. Whereas a normal muscular structure was detected in the smaller CIA, a calcified pattern was detected in the larger CIA. Also, interestingly, early atherosclerotic lesions were identified in the larger vessel. It has been thought that this may reduce blood flow, especially in the dominant vessel, resulting in vessel-wall remodeling after the clamping of the cord (
The small sample size and the lack of any macroscopic examinations of the placental and umbilical cord pathologies are some of the limitations of our study. The effect of hypoplastic fetal umbilical artery on the prognosis is difficult to judge definitively due to the small sample size. However, it is known that the fetal prognosis is better for hypoplastic umbilical arteries compared with SUAs. The inadequate number of fetuses with hypoplastic umbilical arteries is a limitation of our study. More extensive studies are needed to determine the effects of hypoplastic fetal umbilical artery on the fetal prognosis. The present study can act as a pioneer for future studies with larger sample sizes. Another limitation of this study was the subjective evaluation criteria used for the dominant and non-dominant fetal CIAs. However, there is no superior technique available for the evaluation of small fetal structures, such as the umbilical and iliac arteries.
In conclusion, our study revealed that the hypoplastic umbilical artery group’s non-dominant CIA had higher RI values in comparison with the contralateral dominant CIA. We did not observe an association between hypoplastic umbilical arteries and placental, umbilical cord, or fetal pathologies.