| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
ORIGINAL RESEARCH |
From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Weill Medical College of Cornell University, New York, New York
 |
ABSTRACT |
|---|
TOP
 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
METHODS: A retrospective, case-controlled study in which 84 singleton pregnancies with an isolated single umbilical artery were compared with 3-vessel umbilical cord fetuses as the control group.
RESULTS: There was no statistical difference between the groups in maternal demographic data, except for ethnicity and neonatal outcomes, respectively. The mean newborn birth weight was similar between the isolated single umbilical artery and the control groups, 3,268 ± 596 g and 3,274 ± 627 g, respectively. The prevalence of SGA newborns was 7.1% (6 of 84) in the isolated single umbilical artery group and 4.8% (4 of 84) in the control group. An ultrasound examination demonstrated fetal growth restriction in 50% of cases (3 of 6) in the isolated single umbilical artery group and in 25% of subjects (1 of 4) in the control group, respectively.
CONCLUSION: Fetuses with an isolated single umbilical artery are at similar risk for SGA compared with fetuses with 3-vessel umbilical cords. It appears that antepartum serial ultrasound examination does not provide more information for interval fetal growth assessment in fetuses with an isolated single umbilical artery.
LEVEL OF EVIDENCE: II-2
Ultrasonography will also miss some cases of single umbilical artery. Because there are both undetected cases of single umbilical artery as well as false-positive cases, the populations of fetuses suspected of having single umbilical artery and neonates with documented single umbilical artery are different. Based on 2 studies, the proportion of identified fetuses with associated malformations diagnosed prenatally would rise from 26% and 43% prenatally to 43% and 50% postnatally, respectively.3,4 In addition to associated fetal anomalies with an single umbilical artery, intrauterine fetal growth restriction (IUGR) was observed more frequently in aneuploid than euploid fetuses (28% versus 15–20%, respectively).5 In those euploid fetuses with an isolated single umbilical artery, IUGR was also observed in 15–18% of cases;3,4 25–29% of these neonates with an isolated single umbilical artery had a birth weight less than 2,500 g.5,6
The difference in birth weights was even more pronounced in multifetal gestations in which one of the twins had single umbilical artery. Those twins were, on average, 500 g smaller than the co-twins with 3-vessel cords. The mean birth weights were 1,730 g and 2,280 g, respectively.5 From these reports, it appears that fetuses with a isolated single umbilical artery are at increased risk for IUGR, as well as being small for gestational age (SGA) at birth.
Finally, isolated single umbilical artery was present in 16.2% of neonates found to have an anomaly that was not detected prenatally by ultrasonography. In 54.5% of these neonates, however, the anomalies were minor or self-limiting.7 Therefore, in fetuses with an isolated single umbilical artery, serial sonograms for fetal growth and close obstetric follow-up have been recommended.3
The main goal of our study was to evaluate the ultrasound and birth records of all fetuses and neonates with prenatally diagnosed isolated single umbilical artery at our institution in the last 5 years and assess the fetal growth patterns and the prevalence of SGA neonates.
|
MATERIALS AND METHODS |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
For a control group, we used the next consecutive birth of an infant, age-matched and without phenotypic features suspicious for aneuploidy. These neonates all had a confirmed 3-vessel umbilical cord at birth. Gestational age was determined in relation to the estimated date of confinement, defined as 280 days from the last menstrual period and either less than 7 days discrepant from a first-trimester ultrasound examination or 14 days discrepant from a second-trimester ultrasound. Otherwise, the estimated date of confinement from the earliest ultrasound was used.
Fetal biometric parameters, including biparietal diameter, head and abdominal circumference, and femur length, were measured in all pregnancies using 3–6 MHz transabdominal transducers (Acuson 128 XP/4 and Sequoia System 512; Acuson, a Siemens Company, Mountain View, CA). Estimated fetal weight was calculated with the software programs, Clicks 4.0 Medical Information System (Roshtov Software, Englewood, NJ) and AS OBGYN Computerized Patients Records (version 4.972.19, 2002; AS Software, Englewood, NJ). Both software programs used Brenner's curve for standard fetal growth of the United States’ population.8 Therefore, estimated fetal and neonatal birth weights were plotted against Brenner's curve and were reported as the fetal/neonatal weight in grams (g) with corresponding percentile value.
Ultrasound and medical records were reviewed for demographic and outcome data. All fetuses with an estimated fetal weight and neonates with a birth weight below the 10th percentile of Brenner's curve were considered to have in utero growth restriction and/or were categorized as SGA, respectively. Although an estimated weight below the 10th percentile identifies some fetuses without pathological growth restriction and does not include others with this condition, in this study IUGR was used to describe fetal growth below the 10th percentile only. Neonatal birth weights were not adjusted for gender.
In terms of power analysis for our study, we made the following assumptions: The prevalence of growth restriction or SGA in newborns with an isolated single umbilical artery is 20%,3,4 and the expected prevalence of SGA in the general population with 3-vessel umbilical cords is 10% (using the cutoff value of 10th percentile). Therefore, a calculated difference in proportion of SGA neonates between these 2 groups would be 0.10 (10%). To detect a difference in proportion of 0.10, with 80% power at a significance level of .05 (2-tailed), we would need 300 patients in each group. If the actual difference is 20%, we would need only 100 patients per group.
Statistical analysis was performed using Prism 3.02. (GraphPad Software, San Diego, CA). The mean birth weights and the number of SGA fetuses between compared groups were analyzed by the paired t test and the McNemar 
2 test, respectively. Arithmetic mean, standard deviation (SD), median with 25th and 75th quartiles, and range of values for recorded variables were employed as needed to present maternal demographic, fetal, and neonatal data. The Institutional Review Board of Weill Cornell University evaluated and approved the study.
|
RESULTS |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
We observed a total of 141 of 29,856 patients (0.47%) with a single umbilical artery. However, the prevalence of an isolated single umbilical artery, diagnosed prenatally and confirmed at the time of the delivery, was 0.28% (84 of 29,856). There was no statistical difference between the groups in maternal demographic data, except for ethnicity and neonatal outcomes (Table 1). The mean maternal age of all patients was 31.3 ± 5.6 years. The mean newborn birth weight of both groups was 3,276 ± 607 g (range 805–4,595 g), with no statistical significance between the compared groups. The majority of the patients had a spontaneous vaginal delivery (67%, 106/141); 52 patients were operatively delivered (33%), 46 (29.1%) via cesarean delivery, 4 (2.5%) with forceps, and 2 with vacuum-assisted vaginal delivery (1.3%).
|
Table 2 presents prenatal ultrasound data for isolated single umbilical artery and control groups of fetuses, as well as ultrasound-detected IUGR rate and the SGA prevalence at birth. Overall, an estimated date of confinement was determined in 76.2% pregnancies (128/168) on the basis of a last menstrual period that was confirmed with a first- or second-trimester sonogram. In 34 patients (20.2%), gestational age was established from a second-trimester sonogram, whereas 3.6% of patients (6/168) had no prenatal ultrasound examination. In these patients, gestational age was established by menstrual history only. These 6 patients were all from the control group of fetuses with 3-vessel umbilical cords. Overall, 44.0% (74/168) of fetuses had 1 prenatal ultrasound evaluation; 23.2% (39/168) and 29.2% (49/168) had 2 or more ultrasound examinations, respectively. The comparison between the groups demonstrated a statistical difference for gestational dating criteria (P = .044), as well as for the number of prenatal ultrasound examinations (P < .001).
|
The prevalence of SGA at birth was 7.1% (6/84) in the isolated single umbilical artery group of patients and 4.8% (4/84) of newborns with a 3-vessel umbilical cord. This difference was not statistically significant (P = .752, 95% confidence interval –5.63 to 8.95%). When the ultrasound records of the SGA fetuses were evaluated, it was noted that 50% (3 of 6) of the fetuses in the isolated single umbilical artery group and 25% (1 of 4) of the fetuses in the control group had estimated fetal weight below the 10th percentile in utero. Of the 3 fetuses with isolated single umbilical artery without in utero evidence of growth restriction, all had more than 2 ultrasound evaluations, with the final fetal weight assessment in the range of 24–34th percentile of the growth curve at 34–36 weeks of gestational age.
Figure 1 demonstrates growth curves in 6 fetuses with isolated single umbilical artery plotted against Brenner's curve for standard fetal growth. In the control group of patients with SGA neonates at birth, 1 patient had no ultrasound examinations; 2 of 4 fetuses had 1 prenatal ultrasound at 20–21 gestational weeks with fetal weight estimation in range of 42–52nd percentile of the growth curve; and 1 fetus (25%) had 2 prenatal ultrasounds, with final estimated fetal weight less than the 10th percentile at the 37th gestational week.
|
The majority of infants (92.8%, 78/84) with isolated single umbilical artery had an abdominal/kidney ultrasound examination within 3 days of delivery to exclude any associated genitourinary abnormality that would be identifiable by ultrasound evaluation. No genitourinary abnormalities were identified. In addition, no neonates in either group had any dysmorphic features suggestive of aneuploidy.
|
DISCUSSION |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
In 93.7% of infants with isolated single umbilical artery, postnatal renal ultrasonography was performed and revealed no genitourinary abnormalities. This finding contradicts a previous report7 of a higher rate of renal malformations diagnosed postnatally in association with isolated single umbilical artery, although this study was limited by the fact that evaluation was done by postnatal ultrasound examination only. None of the neonates with isolated single umbilical artery had any dysmorphic features on examination. Therefore, cytogenetic studies to exclude aneuploidy were not warranted.
Our results also demonstrated no difference in fetal growth patterns between fetuses with an isolated single umbilical artery and those with a 3-vessel umbilical cord. The incidence of SGA neonates in the isolated single umbilical artery group of 7.1% was 3-fold less than previously published. In contrast, the rate of SGA in the control group of 4.8% was similar to the rate of 5% reported by Heifetz.6 Our findings contradict previous reports of an increased IUGR/SGA rate in fetuses/neonates with isolated single umbilical artery. In a group of euploid fetuses with an isolated single umbilical artery, Catanzarite et al3 described a prevalence of IUGR of 18% (7 of 38) at 22–32 weeks of gestational age. In this study, however, there was no postnatal confirmation of growth deficiency. Other authors reported similar rates of IUGR of 15–26% when single umbilical artery was diagnosed postnatally.5,6 Leung and Robson5 noted that neonatal low birth weight is common and complicated 28% of all cases of single umbilical artery and 15–20% of cases when no associated anomalies were seen. Similarly, Bryan and Kohler10 observed SGA prevalence at birth of 21.9% (25 of 114) in otherwise normal neonates. The higher prevalence of fetal growth restriction or SGA neonates has been related to a possible reduction in cytoplasmic mass caused by nutritional deprivation, rather than the total cell reduction that is usually seen in malformed fetuses with an early IUGR.6
Although we are unable to clearly explain a lack of difference in IUGR/SGA rates between the isolated single umbilical artery and the 3-vessel umbilical cord group, it may be due to the limitations of our study. First, based on our power analysis, there were too few cases of single umbilical artery to detect a significant difference of the magnitude seen. The calculated difference between SGA rates in the 2 compared groups was only 2.38%; therefore, this study had only a 5% power to detect a statistical significance at an 
level of < .05. The major reason was that we were unable to collect the required number of 300 fetuses in each group because of the small prevalence of SGA in our sample of patients.
In addition, there was a statistical difference in maternal ethnic background between the groups that could be associated with different fetal growth patterns and birth weights, especially because we did not adjust the fetal estimated and neonatal birth weights for gender or ethnicity. Therefore, it is possible that socioeconomic factors could be a cause of a lower SGA rate in the group with an isolated single umbilical artery.
Thirdly, in the control group of patients, 7.1% of fetuses had no ultrasound evaluation, and due date was established by last menstrual period only. This subgroup of patients, with suboptimal dating, could have affected the observed SGA prevalence and noted lack of difference between the compared groups.
The fact that we overestimated the number of isolated single umbilical artery fetuses antenatally does not seem to explain the lack of difference between the rates of IUGR/SGA between the 2 groups. At our institution, the fetal anatomy ultrasound scan is performed between 18 and 23 weeks, and a 3-vessel umbilical cord is verified with color Doppler at the level of fetal bladder. When single umbilical artery is suspected, a careful fetal anatomy survey is conducted to exclude associated fetal anomalies. In the absence of any associated fetal anomalies, fetuses are categorized as having an isolated single umbilical artery. Follow-up is at the discretion of the referring physician, most of whom have the patients return in the third trimester to assess fetal growth. When fetal growth restriction is suspected, fetal surveillance is typically initiated. After delivery of the infant with isolated single umbilical artery, a neonatal renal sonogram is typically performed to confirm the presence of both kidneys and exclude any genitourinary anomalies.
Although serial sonography to evaluate fetal growth is commonly performed after the diagnosis of single umbilical artery, half of the fetuses with isolated single umbilical artery had only 1 or 2 ultrasound examinations. Therefore, it is not surprising that some IUGR fetuses were undiagnosed in utero. Because many patients with third-trimester ultrasonography were not examined beyond 34 weeks, IUGR occurring later in gestation would also go undetected. Nevertheless, the numbers of IUGR fetuses in both groups were too small for any feasible statistical analysis of ultrasound detection rates.
In conclusion, according to our data it appears that fetuses with an isolated single umbilical artery appear to be at similar risk for IUGR/SGA compared with fetuses with a 3-vessel umbilical cord. It also appears that antepartum serial ultrasound examination may not be indicated for interval fetal growth assessment in fetuses with an isolated single umbilical artery. However, because of the inadequate power analysis in the present study, future studies with larger numbers of patients are required in this regard.
|
Footnotes |
|---|
Received October 13, 2004. Received in revised form January 12, 2005. Accepted January 19, 2005.
doi:10.1097/01.AOG.0000158108.51397.f5
|
REFERENCES |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
2. Kasznica J, Carlson JA, Coppedge D. Ectrodactyly, retrognathism, abnormal ears, highly arched palate, spina bifida, congenital heart defect, single umbilical artery. Am J Med Genet 1991;40:414–16.[Medline]
3. Catanzarite VA, Hendricks SK, Maida C, Westbrook C, Cousins L, Schrimmer D. Prenatal diagnosis of the two-vessel cord: implications for patient counseling and obstetric management. Ultrasound Obstet Gynecol 1995;5:98–105.[Medline]
4. Jauniaux E, De Munter C, Pardou A, Elkhazen N, Rodesch F, Wilkin P. Evaluation echographique du syndrome de l'artere ombilicale unique: une serie de 80 cas. J Gynecol Obstet Biol Reprod 1989;18:341–8.[Medline]
5. Leung AKC, Robson WLM. Single umbilical artery: a report of 159 cases. Am J Dis Child 1989;143:108–11.[Abstract]
6. Heifetz SA. Single umbilical artery: a statistical analysis of 237 autopsy cases and review of the literature. Perspect Pediatr Pathol 1984;8:345–78.[Medline]
7. Thummala MR, Raju TN, Langenberg P. Isolated single umbilical artery anomaly and the risk for congential malformations: a meta-analysis. J Pediatr Surg 1998;33:580–5.[Medline]
8. Brenner WE, Edelman DA, Hendricks CH. A standard of fetal growth for the United States of America. Am J Obstet Gynecol 1976;126:555–64.[Medline]
9. Herrmann UJ, Sidiropoulos D. Single umbilical artery: prenatal findings. Prenat Diagn 1988;8:275–80.[Medline]
10. Bryan EM, Kohler HG. The missing umbilical artery I. Prospective study based on a maternity unit.. Arch Dis Child 1974;49:844–52.[Medline]
This article has been cited by other articles:
|
|
 |
|
  R. Hershkovitz, E. Sheiner, and M. Mazor Middle cerebral artery blood flow velocimetry among healthy fetuses with a single umbilical artery. J. Ultrasound Med., November 1, 2006; 25(11): 1405 - 1408. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
