Umbilical Cord
Questions Received:
Responses:
I am twenty-two weeks pregnant. At my twenty-week pre-natal visit, my doctor said that they were unable to see all three blood vessels in my baby's umbilical cord during the routine 18-week ultrasound exam. She said that it is not unusual to not be able to see all three at that time. She was not concerned and scheduled me for another ultrasound at 24 weeks to look at the umbilical cord again. Otherwise, my baby seems to be growing according to schedule and everything else looked good. Should I be concerned?
10th June 1999
I am assuming that two umbilical vessels were identified during the ultrasound scan at 18 weeks: a single umbilical artery and an umbilical vein. Generally, one would expect to find two umbilical arteries accompanying the umbilical vein by this stage. (During the embryonic period there are two arteries and two veins, but then one vein disappears.) However, the ultrasound finding in your case may simply reflect the technical difficulty of resolving tiny vessels within a convoluted umbilical cord - the instrument is being used close to the limit of its resolution for such a task. So it could be that by the time of the next scan three umbilical vessels will be visible as a result of the increase in their size during the interim and therefore better visualisation by ultrasound.
On the other hand, the presence of two umbilical vessels may be confirmed at the next scan, rather than three. It is the case that some developmental problems are linked with the presence of a single umbilical artery. However, in a greater proportion of occurrences of single umbilical artery the baby is completely healthy and the presence of a single artery is an unexplained variation of no clinical consequence. I believe you can take comfort from the advice given by your doctor that all the other signs are good, and try not to feel concerned.
I have suffered a still birth at age 32 with my second baby due severe early onset PE. One of the findings in the pregnancy was that I have a single umbilical artery. My question is that could single umbilical artery cause severe PE and placental abnormalities or could this happen again in future pregnancies?
30th June 2000
The presence of a single umbilical artery in the umbilical cord of the baby is sometimes associated with pre-eclampsia in the mother (eg: Sener et al, 1997), but there is no evidence at present of a causal link between the two. The latest proposal about the cause of pre-eclampsia is over-production by the placenta of a signalling molecule identical to neurokinin B (see 'Talking Point'), and other possible causes are outlined in one of our previous answers about pre-eclampsia (click here to see the answer).
Most umbilical cords contain three blood vessels: two umbilical arteries carrying blood from the baby to the placenta and a single umbilical vein returning blood from the placenta to the baby. In many cases of single umbilical artery, the baby develops completely normally and the single artery is able to compensate for the one that is missing (Parilla et al, 1995). However, there is indeed a greater risk than normal that there will be associated developmental problems for the baby such as reduced prenatal growth, chromosomal anomalies, and birth defects, resulting in premature delivery and even death of the baby (Byrne and Blanc, 1985; Jauniaux et al, 1989; Lilja, 1992; Geipel et al, 2000). In one study, approximately one third of fetuses with single umbilical artery had structural defects, mostly affecting the heart (Chow, Benson, and Doubilet, 1998). The left umbilical artery is more commonly absent than the right artery (Abuhamad et al, 1995).
With regard to the likelihood of the problems you have experienced happening again in future pregnancies, it will be worth discussing this with your doctor who will have a more complete understanding of your situation.
References
Abuhamad, A.Z., Shaffer, W., Mari, G., Copel, J.A., Hobbins, J.C., and Evans, A.T. (1995) Single umbilical artery: does it matter which artery is missing? European Journal of Cardio-Thoracic Surgery, 173(3 Pt 1), 728-732 (Sep).
Byrne, J., and Blanc, W.A. (1985) Malformations and chromosome anomalies in spontaneously aborted fetuses with single umbilical artery. American Journal of Obstetrics and Gynecology, 151(3), 340-342 (Feb 1).
Chow, J.S., Benson, C.B., and Doubilet, P.M. (1998) Frequency and nature of structural anomalies in fetuses with single umbilical arteries. Journal of Ultrasound in Medicine, 17(12), 765-768 (Dec).
Csecsei, K., Kovacs, T., Hinchliffe, S.A., and Papp, Z. (1992) Incidence and associations of single umbilical artery in prenatally diagnosed malformed, midtrimester fetuses: a review of 62 cases. American Journal of Medical Genetics, 43(3), 524-530 (Jun 1).
Geipel, A., Germer, U., Welp, T., Schwinger, E., Gembruch, U. (2000) Prenatal diagnosis of single umbilical artery: determination of the absent side, associated anomalies, Doppler findings and perinatal outcome. Ultrasound in Obstetrics and Gynecology, 15(2), 114-117 (Feb).
Jauniaux, E., Demunter, C., Pardou, A., Elkhazen, N., Rodesch, F., and Wilkin, P. (1989) Ultrasonic study of the single umbilical artery syndrome. A series of 80 cases. [Article in French] Journal de Gynecologie, Obstetrique et Biologie de la Reproduction, 18(3), 341-347
Lilja, M. (1992) Infants with single umbilical artery studied in a national registry. 2: Survival and malformations in infants with single umbilical artery. Paediatric and Perinatal Epidemiology, 6(4), 416-422 (Oct).
Parilla, B.V., Tamura, R.K., MacGregor, S.N., Geibel, L.J., and Sabbagha, R.E. (1995) The clinical significance of a single umbilical artery as an isolated finding on prenatal ultrasound. Obstetrics and Gynecology, 85(4), 570-572 (Apr).
Sener, T., Ozalp, S., Hassa, H., Zeytinoglu, S., Basaran, N., and Durak, B. (1997) Ultrasonographic detection of single umbilical artery: a simple marker of fetal anomaly. International Journal of Gynaecology and Obstetrics, 58(2), 217-221 (Aug).