Umbilical arteries
Systemic & remnants · SaO2 ~55-58% PO2 20-25 mmHg
Paired branches of the internal iliac arteries that run up the inner anterior abdominal wall beside the bladder to the umbilicus and carry desaturated post-ductal blood back to the placenta, completing the circuit.
Traced from the start
Detail
- Saturation
- ~55-58% (PO2 ~20-25 mmHg), the lowest arterial value in the fetus; cord arterial gas reflects fetal acid-base status
- Origin
- Anterior division of the internal iliac artery; the proximal segment stays patent after birth as the superior vesical artery
- Share
- Carry roughly a third (up to 40%) of combined ventricular output to the placenta
- Closure
- Constrict within seconds to minutes of birth (stretch, cooling, rising PO2) before the vein does; distal segments fibrose over 2-3 months
- Adult remnant
- Medial umbilical ligaments raising the medial umbilical folds; median fold = urachus (allantois), lateral folds = inferior epigastric vessels; the medial inguinal fossa between them is the site of direct inguinal hernia
When it goes wrong
Single umbilical artery on the morphology scan (~1% of pregnancies)
Associated with renal, cardiac and gastrointestinal malformations and trisomy 18; even an isolated finding warrants a postnatal renal ultrasound
Umbilical artery Doppler with absent or reversed end-diastolic flow
High placental resistance and severe fetal compromise; indication for intensive surveillance or delivery
Paired cord gases at a compromised delivery
Arterial pH below 7.0 with base deficit of 12 mmol/L or more defines significant metabolic acidaemia and supports a diagnosis of hypoxic-ischaemic encephalopathy
Practise this structure
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