Sonographic evaluation of antenatal umbilical coiling index and its association with adverse pregnancy outcomes: A prospective cohort study

Abstract

BACKGROUND:

The umbilical cord coiling index (UCI) is a critical indicator of fetal well-being and pregnancy outcomes. Aberrant umbilical coiling patterns, including hypo- and hypercoiling, have been associated with adverse perinatal sequelae. This study aimed to elucidate the relationship between antenatal UCI (aUCI) and perinatal outcomes in an Indian cohort.

MATERIAL AND METHODS:

A prospective cohort study conducted at a tertiary care center in India enrolled 1200 pregnant women between 18 and 23 weeks of gestation. Standardized ultrasound examinations were performed to assess aUCI. Participants were stratified into hypocoiled, normocoiled, and hypercoiled groups based on UCI percentiles. Multivariate logistic regression analyses, adjusted for maternal demographic and obstetric confounders, were used to evaluate associations between aUCI categories and perinatal outcomes.

RESULTS:

The study estimated a prevalence of 12.72% for hypocoiling and 10.30% for hypercoiling within the cohort. Hypocoiling demonstrated a significant association with increased risk of preterm birth (adjusted odds ratio [aOR]=2.87, 95%[CI]: 1.85-4.45) and intrauterine growth restriction (IUGR). Hypercoiling exhibited more severe associations, including profound IUGR (aOR = 14.31, 95% CI: 9.33-21.94), low birth weight (aOR = 2.28, 95% CI: 1.47-3.55), and adverse neonatal outcomes such as low APGAR scores and neonatal intensive care unit admissions.

CONCLUSION:

This study substantiates the pivotal role of aUCI in predicting adverse perinatal outcomes within the Indian population. The distinct risk profiles associated with hypo- and hypercoiling suggest divergent pathophysiological mechanisms, underscoring the necessity for tailored clinical management strategies based on aUCI findings. These results have significant implications for antenatal surveillance and risk stratification in obstetric practice.

Introduction

The umbilical cord, a vital lifeline between mother and fetus, has long fascinated researchers and clinicians alike. Its helical structure, first described centuries ago, continues to be a subject of intense investigation due to its potential implications for fetal well-being and pregnancy outcomes.[1] In recent years, the umbilical coiling index (UCI) has emerged as a promising marker for assessing fetal health and predicting various perinatal complications.[2]

Umbilical cord coiling is believed to arise from a complex interplay of genetic, environmental, and hemodynamic factors.[3] The UCI, defined as the number of complete coils per centimeter of cord length, provides a quantitative measure of this coiling pattern.[4] Notably, advances in ultrasonography have enabled the assessment of UCI antenatally (aUCI), offering a potential tool for early risk stratification in pregnancy management.[5]

The clinical significance of abnormal cord coiling has been increasingly recognized in recent literature. Both hypocoiling (decreased coiling) and hypercoiling (excessive coiling) have been associated with adverse perinatal outcomes, albeit through potentially different mechanisms.[6] Hypocoiling may compromise the cord’s tensile strength, increasing susceptibility to compression, and subsequent fetal distress.[7] Conversely, hypercoiling has been linked to reduced umbilical blood flow, potentially leading to growth restriction and other complications.[8]

Several studies have reported associations between abnormal aUCI and outcomes such as preterm birth (PTB), low birth weight (LBW), and fetal growth restriction.[9,10] However, the strength and consistency of these associations vary across populations, and their predictive value remains a subject of debate.[11] Moreover, the majority of research has been conducted in Western populations, leaving a significant knowledge gap regarding the applicability of aUCI in diverse ethnic groups.[12]

The need for robust, population-specific data on aUCI is particularly acute in developing countries, where resource constraints often limit access to advanced fetal monitoring techniques.[13] In India, where perinatal mortality rates remain high despite improvements in maternal care, the identification of cost-effective screening tools is of paramount importance.[14]

This study aims to address these knowledge gaps by investigating the associations between aUCI and a comprehensive range of perinatal and fetal outcomes in a large Indian cohort. By providing detailed data on the prevalence of abnormal cord coiling and its relationship with adverse outcomes, we seek to contribute to the growing body of evidence on the clinical utility of aUCI as a screening tool. Furthermore, we aim to explore potential population-specific factors that may influence these associations, paving the way for more personalized approaches to antenatal risk assessment.

Material and Methods

Study up and Design: We conducted a prospective cohort study at Apollo Hospitals, a tertiary care center in Hyderabad, India, from October 2020 to August 2023.

Participants in the Study and Sampling: Pregnant women attending the antenatal clinic for routine second-trimester ultrasonography were screened for eligibility. Inclusion criteria were maternal age ≥18 years, singleton pregnancy, gestational age between 18 and 23 weeks based on last menstrual period, and early ultrasound dating. Exclusion criteria included multiple pregnancies, known fetal anomalies, preexisting maternal medical conditions (e.g. chronic hypertension, diabetes mellitus), and inability to provide informed consent.

Sample size was calculated using G*Power software (version 3.1.9.4).[15] Based on previous studies,[9,10] we estimated a minimum odds ratio of 1.5 for the association between abnormal aUCI and adverse outcomes, with an alpha of 0.05 and power of 0.90. This yielded a required sample size of 1,090 participants. To account for potential loss to follow-up, we aimed to recruit 1,200 women.

Data Gathering Instruments and Techniques: At enrollment, participants completed a structured questionnaire capturing demographic information, medical history, and obstetric history. Maternal anthropometric measurements (height, weight, BMI) were recorded following standardized protocols.[16]

Ultrasound Assessment: All ultrasound examinations were performed using a Philips Epiq 7G ultrasound system with a C5-1 curved array transducer (Philips Healthcare, Amsterdam, Netherlands). Two experienced sonographers (each with >5 years of experience in obstetric ultrasonography) conducted the scans following a standardized protocol based on the INTERGROWTH-21^st consortium guidelines.[17]

Umbilical Cord Assessment: For aUCI measurement, a free loop of umbilical cord was visualized in longitudinal section, ensuring that the imaging plane was perpendicular to the cord’s long axis. At least three complete coils were captured in each image. The distance between the inner edges of the arterial or venous walls of adjacent coils was measured using built-in calipers. Three measurements were taken and averaged to calculate the mean coil distance. The aUCI was calculated as the reciprocal of this distance (aUCI = 1/coil distance in cm).[18]

Quality Control: To ensure measurement consistency, both sonographers underwent a standardized training program prior to study commencement. Intra- and interobserver variability were assessed on a subset of 50 participants, with intraclass correlation coefficients calculated to ensure acceptable reliability (ICC > 0.80).[19]

Classification of Umbilical Cord Coiling: Based on the calculated aUCI values, participants were classified into three groups: hypocoiled: aUCI <10^th percentile of the study population, normocoiled: aUCI between 10^th and 90^th percentiles, and hypercoiled: aUCI >90^th percentile.

Follow-Up and Outcome Assessment: Participants were followed throughout their pregnancy with routine antenatal care as per institutional protocols. Perinatal outcomes were recorded at delivery and during the immediate postpartum period. Primary outcomes included PTB (delivery <37 weeks gestation), LBW (<2500 grams), and admission to neonatal intensive care unit (NICU). Secondary outcomes encompassed the mode of delivery (vaginal vs. cesarean), fetal heart rate abnormalities during labor, meconium-stained amniotic fluid, APGAR scores at 1 and 5 minutes, and Intra-Uterine Growth Restriction (IUGR, defined as estimated fetal weight <10^th percentile for gestational age).

Data Analysis: Data analysis was performed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics were presented as means ± standard deviations for continuous variables and percentages for categorical variables. Differences in baseline characteristics across aUCI groups were assessed using one-way ANOVA for continuous variables and Chi-square tests for categorical variables.

The associations between aUCI categories and perinatal outcomes were evaluated using multivariate logistic regression models, adjusting for potential confounders identified a priori based on literature review and clinical relevance. These included maternal age, BMI, parity, smoking status, and gestational age at delivery (for nonpreterm outcomes). The results were presented as adjusted odds ratios (aOR) with 95% confidence intervals (CI).

To explore potential nonlinear relationships between aUCI and outcomes, restricted cubic spline analyses were performed.[20] Sensitivity analyses were conducted to assess the robustness of findings, including stratification by parity and exclusion of participants with pregnancy complications.

All statistical tests were two-sided, with P values < 0.05 considered statistically significant. To address multiple comparisons, we applied the Benjamini–Hochberg procedure to control the false discovery rate at 5%.[21]

Ethical Consideration: The research received institutional approval from the Ethics Committee (IEC) of the Apollo Institute of Medical Sciences and Research, Hyderabad, via IRB no (AHJ-ACD-019/07-20). Implied consent was obtained from the subjects, and anonymity and confidentiality of data were ensured.

Results

A total of 1242 participants attending the Department of Obstetrics and Gynaecology, <name blinded > for antenatal check-ups in the second trimester (18–23 weeks) were recruited. Of these, 1200 participants with live births were included in the final analysis [Figure 1]. Table 1 presents the characteristics of participants and those lost to follow-up.

Figure 1.

Study participants recruited in each visit and their follow-up

Table 1.

Comparison of baseline characteristics of study participants with respect to those lost to follow-up

Maternal Factors		Total (n=1242)		Participants (n=1200)		Lost to follow-up (n=42)		P
Age (yr)		25.23±4.01		25.67±4.01		24.92±3.89		0.42
Gravida
Primigravid		685 (55.15)		660 (55.00)		25 (59.52)		0.24
Multigravid		557 (44.84)		540 (45.00)		17 (40.47)		0.56
ANC (Wk)		20.42±1.43		20.66±1.36		20.12±1.42		0.78
Weight (kg)		60.03±8.28		60.25±8.09		59.23±8.56		0.43
Height (cm)		150.87±32.18		151.23±34.65		150.45±33.87		0.59
BMI (kg/m2)		20.04±2.69		20.23±2.43		19.54±1.98		0.32
Coiling Index
Hypocoiled		158 (12.72)		152 (12.66)		6 (14.28)		0.77
Normocoiled		956 (76.97)		923 (76.92)		33 (78.57)
Hypercoiled		128 (10.30)		125 (10.42)		3 (7.14)
Distance between Coils (cm)		3.17±1.20		3.21±0.91		2.98±1.01		0.18
Length of Cord (cm)		58.34±9.25		59.25±8.09		57.87±8.12		0.76

ANC: Antenatal Check-up; BMI: Body Mass Index *P<0.05

The mean umbilical cord coiling index was 0.51 ± 0.16, with the 10^th and 90^th percentiles at 0.26 and 0.40, respectively. The mean distance between coils was 3.17 ± 1.20 cm. In our cohort, the prevalence of hypocoiling was 12.72%, while hypercoiling occurred in 10.30% of cases.

The majority of study participants (59.31%) were between 18 and 22 years old, with 10.37% being teenage pregnancies. The mean age was 25.23 ± 4.01 years. Educational attainment varied, with 63.64% completing higher secondary education and 14.18% completing primary education. Only 1.97% of participants were employed, with the remainder being homemakers. No participants reported a history of substance use. Primigravidae constituted 55% of the cohort. Among multigravidae, 40.3% conceived within 1–2 years of their previous pregnancy, while only 33.5% maintained the recommended birth interval of three years or more.

Baseline characteristics did not differ significantly between women with hypo- or hypercoiled cords and those with normocoiled cords [Table 2] PTB occurred in 11.33% of the cohort, with 30 cases attributed to preterm premature rupture of membranes, preterm labor, preeclampsia, IUGR, or a combination thereof. Notably, a significant association with PTB was observed only in the hypocoiled group (OR = 2.87, 95% CI: 1.85 – 4.45; P < 0.05).

Table 2.

Baseline characteristics of study participants stratified by coiling index

Maternal Factors		Normocoiled (n=923)		Hypocoiled (n=152)		Hypercoiled (n=125)		P
Age (yr)		25.58±4.01		25.74±3.92		26.22±4.06		0.24
ANC (Wk)		20.66±1.35		20.60±1.38		20.71±1.39		0.80
Weight (kg)		59.62±7.71		61.44±10.02		61.57±4.98		0.23
Height (cm)		149.21±23.65		152.12±24.72		150.34±22.76		0.76
BMI (kg/m2)		19.87±2.65		20.87±2.12		20.12±1.87		0.18
Distance between Coils (cm)		3.05±0.34		5.16±0.91		2.06±3.21		<0.01*
Length of Cord (cm)		58.62±7.71		64.44±10.21		57.57±4.98		<0.01*
Gravida
Primigravid		514 (55.68)		86 (56.57)		60 (48.00)		0.24
Multigravid		409 (44.31)		66 (43.42)		65 (52.00)

ANC: Ante natal Check-up; BMI: Body Mass Index*: P<0.05

Neonatal birth weight was significantly associated with cord coiling classification. Initially, neonates with hypocoiled cords weighed significantly less than those with normocoiled cords (P < 0.05); however, this association lost significance after controlling for confounders. Conversely, neonates with hypercoiled cords maintained significantly lower birth weights compared to those with normocoiled cords, even after adjustment (P < 0.05). The odds of delivering a LBW neonate were 2.28 times higher in the hypercoiled group compared to the normocoiled group.

No significant relationship was observed between amniotic fluid index and cord coiling. Additional associations with adverse outcomes are detailed in Table 3.

Table 3.

Results of multivariate logistic regression analysis on perinatal and fetal outcomes of study participants stratified by coiling index

Outcomes		Total (n=1200)		Normocoiled (n=923)		Hypocoiled (n=152)		aORa		P a		Hypercoiled (n=125)		aORb		P b
Abnormal FHR %		217 (18.08)		148 (16.03)		36 (23.68)		0.86 (0.50–1.49)		0.60		33 (26.40)		1.88 (1.21–2.94)		<0.05*
Abruptio Placentae %		16 (1.33)		12 (1.30)		4 (2.63)		2.05 (0.65–6.44)		0.21		0 (0.00)		0.29 (0.01–4.9)		0.39
Post Partum Hemorrhage %		45 (3.75)		7 (0.11)		28 (18.42)		1.54 (0.66–3.59)		0.31		10 (8.00)		2.77 (1.31–5.87)		<0.05*
Hydramnios
Oligohydramnios %		60 (5.00)		46 (4.98)		8 (5.26)		1.05 (0.48–2.29)		0.88		6 (4.80)		0.96 (0.40–2.29)		0.92
Polyhydramnios %		60 (5.00)		42 (4.55)		10 (6.57)		1.47 (0.72–3.01)		0.28		8 (6.40)		1.43 (0.65–3.12)		0.36
Meconium Stained Liquor %		243 (20.25)		171 (18.52)		37 (24.34)		1.41 (0.94–2.12)		0.09		35 (28.00)		1.71 (1.11–2.61)		0.01*
Direction of Coil
Sinistral %		458 (38.16)		375 (40.62)		45 (29.60)		1.62 (1.12–2.36)		0.01*		38 (30.4)		1.56 (1.04–2.34)		0.02*
Dextral %		742 (61.83)		548 (59.37)		107 (70.39)		-		-		87 (69.6)		-		-
Mode of Delivery
LSCS %		393 (32.75)		274 (29.68)		61 (40.13)		1.58 (1.11–2.26)		0.01*		58 (46.40)		2.05 (1.40–2.99)		<0.05*
VD %		807 (67.25)		649 (70.31)		91 (59.86)		-		-		67 (53.60)		-		-
Preterm Birth %		136 (11.33)		87 (9.42)		35 (23.02)		2.87 (1.85–4.45)		<0.05*		14 (11.20)		1.21 (0.66–2.20)		0.52
IUGR %		147 (12.25)		71 (7.69)		8 (5.26)		1.66 (1.31–5.41)		<0.05*		68 (54.40)		14.31 (9.33–21.94)		<0.05*
Low Birth Weight %		741 (61.75)		556 (60.23)		88 (57.89)		0.90 (0.64–1.28)		0.42		97 (77.60)		2.28 (1.47–3.55)		<0.05*
APGAR Score (At 1 min) % ≤4		288 (24.00)		190 (20.58)		36 (23.68)		1.19 (0.79–1.79)		0.38		62 (49.60)		3.79 (2.58–5.58)		<0.05*
APGAR Score (At 5 min) % ≤7		269 (22.41)		177 (19.17)		37 (24.34)		1.35 (0.90–2.03)		0.14		55 (44.00)		3.31 (2.24–4.88)		<0.05*
Admission to NICU %		490 (40.83)		333 (36.07)		76 (50.00)		1.77 (1.25–2.50)		<0.05*		81 (64.80)		3.26 (2.20–4.82)		<0.05*

aOR: adjusted Odds Ratio; FHR: Fetal Heart Rate; LSCS: Lower Segment Cesarean Section; VD: Vaginal Delivery; IUGR: Intra Uterine Growth Retardation; NICU: Neonatal Intensive Care Unit, *P<0.05. ^aMultivariate logistic regression analysis of hypocoiling with respect to perinatal and fetal outcomes adjusted for confounding factors with P<0.20, ^bMultivariate logistic regression analysis of hypercoiling with respect to perinatal and fetal outcomes adjusted for confounding factors with P<0.20

Image plate 1 illustrates alternating red and blue signals, indicating bidirectional blood flow through helical vessels. The intense coloration and circular arrangement confirm hypercoiling. Multiple tightly spaced coils are visible, presenting as oblique light and dark bands along the cord’s length, consistent with an increased UCI. The complex, intertwined pattern of pronounced red and blue signals further illustrates exaggerated umbilical vessel coiling. These findings suggest altered hemodynamics associated with hypercoiling.

Image 1.

Sonographic Images of Hypercoiled Umbilical Cord

Image plate 2 depicts a longitudinal view of a hypocoiled umbilical cord, appearing as a long, relatively straight structure with minimal visible coiling. This reduced coiling is highlighted by the absence of typical spiral patterns compared to a normal cord. Color Doppler ultrasound shows the cord as a nearly straight line with red (arterial flow) and blue (venous flow) coloration, indicating diminished coiling. Both images illustrate the characteristics of hypocoiling, which can signify potential pregnancy complications and is a significant finding in prenatal ultrasound assessments.

Image 2.

Sonographic Images of Hypocoiled Umbilical Cords

Image plate 3 displays a grayscale ultrasound cross-sectional view focusing on the fetal head or face area. The fetal skull appears as a bright curved line, with discernible facial features. In addition, color Doppler ultrasound visualizes blood flow within the umbilical cord, showing alternating sections of red and blue coloration. This indicates bidirectional blood flow typical of a normally coiled umbilical cord, with vessels twisting in a helical pattern. Red denotes arterial flow toward the probe, while blue indicates venous flow away from the probe. The image is framed within a sector-shaped ultrasound field of view.

Image 3.

Sonographic Images of Normocoiled Umbilical Cords

Discussion

Abnormal umbilical cord coiling has long been associated with adverse perinatal and birth outcomes, although the results have varied across different populations and geographical regions.[8] Our study found a prevalence of hypercoiling (10.30%) and hypocoiling (12.72%) consistent with previous literature.[22,23] The mean coiling index of 0.51 ± 0.16 observed in our cohort aligns with established norms, providing a reliable baseline for our population.[24]

The association between abnormal coiling patterns and adverse outcomes likely reflects mechanical and/or functional malfunctions of the feto-placental unit.[25] Our findings demonstrate that both hypocoiling and hypercoiling are associated with increased risks, albeit with different patterns of adverse outcomes.

Hypocoiling was significantly associated with PTB, a crucial finding given that PTB is a strong indicator of adverse neonatal outcomes.[26] This association may be explained by the increased susceptibility of hypocoiled cords to compression and reduced blood flow, potentially triggering preterm labor.[27] In addition, our study found a significant association between hypocoiling and IUGR, consistent with recent literature suggesting impaired nutrient transfer in hypocoiled cords.[7]

Hypercoiling, on the other hand, was associated with a broader range of adverse outcomes. We observed significant associations with IUGR, LBW, and low APGAR scores at 1 and 5 minutes, and increased NICU admissions. These findings align with recent studies suggesting that excessive coiling may impair blood flow through increased vascular resistance.[28,29] The strong association with IUGR in hypercoiled cords (aOR 14.31) is particularly noteworthy and warrants further investigation.

Our study also revealed an increased risk of abnormal fetal heart rate and postpartum hemorrhage in the hypercoiled group. These associations have been less frequently reported in previous literature and may provide new insights into the consequences of hypercoiling.[30,31]

Interestingly, recent research has highlighted the importance of addressing maternal education needs in postpartum care promotion. A mixed-methods study by Razavian et al. found that tailoring postpartum care based on mothers’ specific educational requirements can lead to improved outcomes.[32] This approach could be particularly valuable in cases where abnormal cord coiling has been identified, as it may help mothers better understand and manage potential risks.

Interestingly, we found a significant association between abnormal coiling (both hypo- and hypercoiling) and sinistral coiling direction. This finding adds to the growing body of evidence suggesting that coiling direction may have clinical significance.[33]

The increased cesarean section rates observed in both hypocoiled and hypercoiled groups compared to normocoiled groups may reflect the higher prevalence of fetoplacental insufficiencies in cases of abnormal coiling.[34] This observation underscores the potential value of antenatal cord coiling assessment in identifying pregnancies at higher risk of requiring interventional deliveries.

It is worth noting that traumatic birth experiences, which may be more common in cases of abnormal cord coiling, can lead to posttraumatic stress disorder (PTSD) in mothers. A study by Alipanahpour et al.[35] found a correlation between traumatic birth experiences and PTSD symptoms, with maternal religious attitudes playing a potential protective role. This highlights the importance of comprehensive maternal care that addresses both physical and psychological aspects of childbirth.

Although our study provides valuable insights, it is not without limitations. The reliance on ultrasonography reports rather than real-time evaluation may have introduced some bias. In addition, the variability of coiling along the cord length and the practical inability to measure coiling over the entire cord are recognized constraints.[36]

Another potential limitation is the variability in triage quality, which could impact the identification and management of high-risk pregnancies. A study by Nazari et al. on the Emergency Severity Index (ESI) triage quality in Iran found that factors such as work experience and education level influenced triage accuracy.[37] While this study focused on general emergency triage, its findings underscore the importance of standardized assessment protocols in obstetric care, including the evaluation of umbilical cord coiling

Limitations and recommendation

Despite these limitations, our study represents one of the largest investigations of umbilical cord coiling and its association with perinatal outcomes in an Indian population. The findings highlight the potential of antenatal UCI as a predictor of adverse perinatal and fetal outcomes. However, before implementing UCI assessment in routine clinical practice, further research is needed to elucidate the factors influencing cord coiling and to account for potential confounders.

Conclusions

Our study reinforces the importance of umbilical cord coiling as a potential marker for adverse perinatal outcomes. The distinct patterns of risk associated with hypocoiling and hypercoiling suggest that these conditions may have different underlying mechanisms and may require different management strategies. Future research should focus on standardizing UCI measurement techniques, investigating the underlying mechanisms of abnormal coiling, and evaluating the cost-effectiveness of incorporating UCI assessment into routine antenatal care. Large-scale, multicenter studies across diverse populations will be crucial in establishing the generalizability of these findings and potentially informing clinical guidelines for high-risk pregnancy management.

Ethics code

The study was approved by the Institutional Ethics Committee (AHJ-ACD-019/07-20), and written informed consent was obtained from all study participants.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.