Single Umbilical Artery in Multiple Gestation: The Answer is A - Multiple Gestation
The most likely cause of single umbilical artery (SUA) in this patient is her history of multiple gestation (twins), as twin pregnancies carry a 4-6 fold increased risk of SUA compared to singleton pregnancies, and this elevated risk is independent of maternal age, parity, or thyroid function. 1
Why Multiple Gestation is the Correct Answer
Twin pregnancies have dramatically elevated SUA rates of up to 4.6% compared to only 0.25-1% in singleton pregnancies. 1 This represents the strongest risk factor among the options provided.
The mechanism behind this association involves:
- Increased placental vascular complexity in twin pregnancies contributes directly to SUA development 1
- Higher rates of placental vascular anastomoses and unequal placental sharing, particularly in monochorionic twins 1
- Greater likelihood of developmental vascular abnormalities when two fetuses share placental territory 1
Why the Other Options Are Incorrect
Maternal Age (Option B)
The evidence explicitly states that the elevated risk of SUA in twins is independent of maternal age 1. While advanced maternal age increases other pregnancy risks, it does not independently increase SUA risk.
Parity (Option C)
Although one population study found that parity ≥4 was associated with increased SUA odds 2, the elevated risk of SUA in twins is independent of parity 1. The patient's history of twins (which is a form of multiparity) is the causative factor, not the parity itself.
Hypothyroidism (Option D)
The elevated risk of SUA in twins is independent of thyroid function 1. There is no established association between hypothyroidism and SUA in the medical literature provided.
Clinical Implications for This Patient
Given the SUA diagnosis in the context of her twin history, the following management is warranted:
- Perform comprehensive fetal anatomic assessment focusing on cardiovascular and renal systems, as these are the most commonly associated anomalies 1
- Schedule third-trimester ultrasound to evaluate fetal growth 1, 3
- Consider weekly antenatal surveillance beginning at 36 weeks gestation, as SUA carries an increased stillbirth risk (OR 4.80) 1, 3
- No additional aneuploidy testing is needed if this is an isolated SUA and prior screening was low-risk 1, 3