Hypocoiled Umbilical Cord: Definition, Incidence, and Clinical Significance
A hypocoiled umbilical cord is defined as an umbilical coiling index (UCI) less than 0.07-0.12 spirals per centimeter (below the 10th percentile), and it carries significant clinical implications including increased risks of preterm delivery, fetal distress, low birth weight, and adverse perinatal outcomes that warrant enhanced fetal surveillance. 1, 2
Definition and Measurement
The umbilical coiling index quantifies the helical pattern of umbilical vessels and is calculated by dividing the total number of complete vascular coils by the umbilical cord length in centimeters. 1, 2
Key parameters:
- Normal UCI: 0.17 ± 0.009 spirals per cm (mean) or 0.24 ± 0.09 in some populations 1, 2
- Hypocoiling threshold: UCI <0.07 to <0.12 (below 10th percentile) 1, 2
- Measurement timing: Can be assessed sonographically during second trimester anatomic survey (18-28 weeks) or postnatally 3, 4
The antenatal UCI (aUCI) measured at 18-20 weeks during routine fetal anatomic survey can serve as a screening tool for at-risk fetuses. 3
Incidence
While the provided evidence does not specify exact population-based incidence rates, hypocoiling represents the lower 10th percentile of the UCI distribution by definition. 1 In studied populations, hypocoiled cords comprised a minority of cases, with the majority falling into the normocoiled category. 2, 3
Clinical Significance and Associated Adverse Outcomes
Maternal Complications
Hypocoiling is significantly associated with:
Fetal and Intrapartum Complications
Intrapartum risks include:
- Fetal heart rate abnormalities and decelerations during labor 1, 2
- Increased operative delivery rates for fetal distress 1
- Abnormal placental cord insertion: 66.7% of hypocoiled cords had abnormal (marginal or velamentous) insertion versus only 1.3% in normally coiled cords 5
Neonatal Outcomes
Hypocoiling significantly increases risk of:
- Preterm delivery: 35-59% incidence in hypocoiled groups versus significantly lower rates in normocoiled groups, with adjusted odds ratio of 9.6 (95% CI 2.09-44.07) 3, 4
- Low birth weight: 36.4-69% of neonates in hypocoiled groups had low birth weight 3, 4
- Mean gestational age at delivery: 36.8 weeks (hypocoiled) versus 38.3 weeks (normocoiled) 3
- Mean birth weight: 2055 grams (hypocoiled) versus 3102 grams (normocoiled) 3
- NICU admission: 27.3% in hypocoiled group versus significantly lower in normocoiled groups 4
- Fetal demise 1
- Anatomic-karyotypic abnormalities 1
Clinical Management Algorithm
When hypocoiled umbilical cord is identified, the American College of Radiology recommends the following surveillance protocol: 6
Enhanced Surveillance Protocol
- Umbilical artery Doppler assessment after 20 weeks gestation 6
- Serial growth ultrasounds every 3-4 weeks 6
- Antenatal testing (NST/BPP) in the third trimester 6
Intrapartum Management
- Continuous electronic fetal monitoring during labor 6
- Lower threshold for interventional delivery if fetal distress develops 6
- Preparation for potential complications given the high association with intrapartum fetal heart rate abnormalities 6, 1
Important Clinical Considerations
The relationship between hypocoiling and adverse outcomes may be bidirectional: It remains unclear whether abnormal coiling directly causes pathology or represents a marker of underlying placental or fetal compromise. 1 Regardless, the strong associations with adverse outcomes justify enhanced surveillance.
Hypocoiling detected at 18-20 weeks anatomic survey can serve as an early screening tool to identify pregnancies requiring closer monitoring throughout gestation. 3
The mechanism of protection: Normal coiling provides structural support and protection to umbilical vessels through the helical pattern, along with Wharton's jelly and amniotic fluid. 3 Hypocoiling may compromise this protective mechanism, potentially explaining increased vulnerability to compression and vascular compromise.