What the finding is

A normal umbilical cord contains three vessels: two arteries carrying blood from the baby to the placenta, and one vein carrying blood back. In a single umbilical artery there is one artery instead of two, so the cord has two vessels rather than three. You may see it written as SUA, as two-vessel cord, or simply described as the cord having two vessels.

It is one of the more common findings at the 20-week scan and is usually spotted in passing rather than looked for. In most pregnancies where it is found, nothing else is abnormal.

Why you may have been told it needs no action

The NHS Fetal Anomaly Screening Programme handbook lists it explicitly among findings that do not generate a referral: "If one or more of the normal variants listed below are seen, the woman does not need referral for further assessment as part of the NHS FASP: choroid plexus cysts; dilated cisterna magna; echogenic foci in the heart; 2 vessel cord."

That is a deliberate national position. Historically, a two-vessel cord prompted discussion of chromosomal testing. It no longer does under the NHS programme when it is an isolated finding, because on its own it adds too little to the chance calculation to justify the anxiety and the interventions that followed.

Why you may also have been booked extra scans

The same handbook page carries a second list, from a different framework, and this is where the apparent contradiction comes from: "Although not part of NHS FASP, some scan findings can be associated with an increased risk of fetal growth restriction (FGR). The Royal College of Obstetricians and Gynaecologists (RCOG) guidance and the NHS England Saving Babies' Lives Care Bundle (SBLCB) require additional assessment for FGR. This includes uterine artery Doppler assessment and an individualised plan of care."

The findings on that list are "echogenic bowel", "estimated fetal weight below the 10th centile", and "single umbilical artery (2 vessel cord)". The handbook adds: "If these findings are seen during the scan, then locally agreed pathways for FGR should be followed."

So both statements you may have heard are correct. No chromosomal referral is needed; growth surveillance is. They come from different documents with different purposes, and nobody has contradicted anybody.

What growth surveillance actually looks like

The handbook names uterine artery Doppler assessment and "an individualised plan of care" as the additional assessment. In practice that usually means serial ultrasound scans measuring the baby's size in the third trimester, often with umbilical artery Doppler, on a schedule set by your maternity unit under the Saving Babies' Lives care bundle and RCOG guidance on the small-for-gestational-age fetus.

Because the schedule is set locally within those national frameworks, the number and timing of scans varies between trusts. Ask for yours in writing, and check the appointments exist rather than assuming they will appear.

What it is not

An isolated single umbilical artery is not a diagnosis of a chromosomal condition, and the NHS programme's own classification of it as a normal variant is the clearest possible statement of that.

It is not caused by anything you did or did not do in early pregnancy. The cord forms very early and this is a variation in how it developed.

It is not a reason to change how you give birth by itself. Where growth is normal on serial scans and there are no other findings, birth planning generally proceeds as it otherwise would.

When the picture changes

What matters is whether the finding is isolated. A single umbilical artery seen alongside other structural findings on the anomaly scan is a different situation from one seen in a scan that is otherwise completely normal, and it will prompt a fetal medicine referral and a wider conversation.

The 20-week scan checks for signs of 11 physical conditions, and the handbook confirms that "all significant findings of the scan are reported". If you were told about the cord and nothing else, that is meaningful information rather than an omission.

Kidneys and the heart are the two areas most often mentioned in connection with a two-vessel cord, and both are examined at the anomaly scan as standard. Some units arrange a repeat detailed look at these; ask whether yours has, and whether anything was seen.

What to watch for between scans

Because the follow-up is about growth, the thing to pay attention to is fetal movement. Any reduction or change in your baby's usual pattern needs same-day assessment, and it should never be saved for the next scheduled scan appointment. That advice applies to every pregnancy, but it carries more weight when growth is already being monitored.

NICE guideline NG201 sets the baseline antenatal schedule that these extra scans are added to, including routine measurement and monitoring at each appointment. Extra scans supplement that; they do not replace the usual contacts.

Questions worth asking at the scan appointment

Four questions get you the whole picture. Was the finding isolated, or was anything else seen? Were the kidneys and the heart both seen clearly? What is the growth surveillance plan, and on what dates? And is a fetal medicine or obstetric review planned, or is this being managed within routine care?

The answers should all be recordable in a sentence each, and they should be in your notes. If your unit follows a written pathway for two-vessel cord, you can ask for a copy — most maternity services have one, because the NHS FASP handbook explicitly hands the follow-up to "locally agreed pathways for FGR".

After the birth

The cord and placenta are examined after delivery as a matter of routine, and a two-vessel cord is confirmed then. Where the pregnancy was otherwise normal and growth was normal, no particular newborn testing follows from the cord finding alone.

Your baby has the standard newborn physical examination within 72 hours, which includes the heart, and the newborn hearing screen and blood spot test on the usual schedule. If anything specific was flagged antenatally about the kidneys or the heart, make sure it is written in the notes that go with you to the postnatal ward, so that the examining clinician knows to look.

Single Umbilical Artery