Electronic Fetal Monitoring and Neonatal Outcomes when a Nuchal Cord Is Present at Delivery

Abstract

Objective

This study aimed to determine the association between nuchal cord, electronic fetal monitoring parameters, and adverse neonatal outcomes.

Study Design

This was a prospective cohort study of 8,580 singleton pregnancies. Electronic fetal monitoring was interpreted, and patients with a nuchal cord at delivery were compared with those without. The primary outcome was a composite neonatal morbidity index. Logistic regression was used to adjust for confounders.

Result

Of 8,580 patients, 2,071 (24.14%) had a nuchal cord. There was no difference in the risk of neonatal composite morbidity in patients with or without a nuchal cord (8.69 vs. 8.86%; p = 0.81). Nuchal cord was associated with category II fetal heart tracing and operative vaginal delivery (OVD) (6.4 vs. 4.3%; p < 0.01).

Conclusion

Nuchal cord is associated with category II electronic fetal monitoring parameters, which may drive increased rates of OVD. However, there is no significant association with neonatal morbidity.

There is continued debate regarding the clinical significance of a nuchal cord (NC) at the time of delivery. Multiple prior studies have concluded that there is no risk of neonatal morbidity associated with an NC.^1–5 However, other studies have reported an increased risk of certain neonatal outcomes including decreased birthweight,^7,8 shoulder dystocia,^6,7 Apgar score < 7,^9–14 neonatal intensive care unit (NICU) admissions,^7,10,11 need for respiratory resuscitation,¹⁰ and fetal distress.^13,14 This uncertainty leads to frustration for providers and patients who often believe that an NC at the time of birth is associated with poor neonatal outcomes.¹⁵

Additionally, despite its ubiquitous use, intrapartum electronic fetal monitoring (EFM) and its association with NC and neonatal outcomes have not been widely studied. Earlier reports have generally been in disagreement and have not systematically examined specific EFM parameters^{1,8,10,13,16–19}; thus, there is a need to further assess the risk of neonatal morbidity in the setting of both NC and EFM parameters.

We studied the association between EFM, NC, and neonatal outcomes among women laboring at term with singleton pregnancies to estimate whether the presence of an NC at the time of delivery was associated with nonreassuring EFM parameters and adverse neonatal outcomes. We hypothesized that women with NC would be more likely to have category II EFM characteristics, such as variable decelerations, than women without NC but both groups would have similar neonatal outcomes.

Materials and Methods

This was a planned secondary analysis of a prospective cohort study of 8,580 women with consecutive singleton pregnancies in labor at or beyond 37^0/7 weeks.²⁰ The primary purpose of the cohort was to examine the relationship between intrapartum EFM and perinatal outcomes. The study was approved by the Washington University Medical School Human Research Protection Office (IRB ID #201102438).

This secondary analysis compared patients with a neonatal NC at the time of delivery with those without. NC was diagnosed at birth and was defined as the umbilical cord wrapped 360 degrees or more around the fetal neck. Exclusion criteria included unknown NC status, major fetal anomaly, scheduled cesarean delivery without labor, failure to reach the second stage with pushing, and gestational age < 37 weeks. Trained research staff collected detailed data from participant’s medical records.

The primary outcome of the study was composite neonatal morbidity, defined as one or more of the following events: neonatal death before hospital discharge, seizure(s), hypoxic-ischemic encephalopathy, need for hypothermic treatment, respiratory morbidity, hypotension requiring vasopressor therapy, and suspected sepsis. A diagnosis of hypoxic-ischemic encephalopathy required moderate-to-severe neonatal encephalopathy, defined by the National Institute of Child Health and Human Development criteria,²¹ or seizure activity) in the setting of an abnormal umbilical artery cord gas (pH < 7.0 or base deficit more than −16), 5-minute Apgar score < 5, or need for respiratory support at 10 minutes of life. Respiratory morbidity included need for ventilator support or respiratory distress diagnosed clinically by nasal flaring, subcostal/intercostal retractions, and need for supplemental oxygen to main oxygen saturation > 95%. Secondary outcomes included components of the composite as well as NICU admission, umbilical artery cord pH < 7, and 5-minute Apgar score < 7.

Gestational age was calculated based on the woman’s first ultrasound examination in the pregnancy and last menstrual period.²² A woman was considered to have diabetes mellitus if she had a diagnosis of type 1 /type 2 in the medical record or gestational diabetes mellitus based on the National Diabetes Group criteria.²³ A hypertensive disorder in pregnancy was defined as chronic hypertension, gestational hypertension, or preeclampsia.²⁴ Maternal and neonatal demographic data obtained from the medical record included type of labor (spontaneous or induced), oxytocin use, mode of delivery (vaginal, cesarean, operative vaginal), use of regional anesthesia, neonatal birth weight, and maternal complications. Maternal complications were classified as those during delivery (shoulder dystocia, fever, retained placenta, and other) or postpartum (wound infection, fever, transfusion, hemorrhage, endomyometritis). Small for gestational age was defined as birth weight < 10th percentile based on the Alexander growth curve reference.²⁵

Obstetric research nurses, formally trained to systematically review EFM patterns using the National Institute of Child Health and Human Development criteria,²⁶ were blinded to all clinical data and extracted EFM patterns in the 120 minutes prior to delivery. These patterns were categorized according to fetal heart rate (FHR) baseline, variability, number of accelerations, and number/type of decelerations.²⁷ Decelerations were considered repetitive if they occurred with ≥50% of uterine contractions in any 20-minute window. Prolonged decelerations were defined as a decrease in FHR from the baseline of ≥15 bpm, lasting between 2 and 10 minutes. The characteristics of EFM patterns were defined and compared using the Eunice Kennedy Shriver National Institute of Child Health and Human Development 3-tier category system.²⁷

Data analysis was performed with descriptive and bivariate statistics using an unpaired Student’s t-test or Mann-Whitney U test for continuous variables and using a chisquare or Fisher’s exact test for categorical variables, as appropriate. The Kolmogorov-Smirnov test was used to test the normal distribution of continuous variables. Rates of the primary and secondary outcomes were estimated within groups. Multivariable logistic regression models for the primary and secondary outcomes were developed to adjust for potential confounders. Covariates that were associated with the presence of NC in bivariable analyses were included in the initial model and were removed sequentially with the use of a backward stepwise approach. Covariates that were considered in the model included advanced maternal age (AMA; maternal age ≥ 35), Black race, obesity(body mass index ≥ 30), diabetes,hypertension, history of previous cesarean delivery, and oxytocin use. Final models included black race and oxytocin use and were tested using the Hosmer-Lemeshow goodness-of-fit test. We explored specific features within the category II FHR patterns to identify whether NC in the setting of specific features conferred risk.

All statistical analyses were performed using STATA software (version 10.0 [special edition], StataCorp, College Station, TX).

Results

Among 8,580 patients meeting the inclusion criteria, 2,071 women (24.14%) had an NC at the time of delivery. Women with an NC at delivery were more likely to be white and of AMA and were less likely to have a prior cesarean delivery (Table 1).

Table 1.

Comparison of baseline characteristics in the presence or absence of a nuchal cord

	Nuchal cord, N = 2,071	No nuchal cord, N = 6,509	p-Value
Maternal age median (IQR)	25 (21–31)	25 (21–30)	<0.01
AMA (≥35 y)	223 (10.77)	541 (8.31)	0.01
Race
Black	1,265 (61.08)	4,300 (66.06)	<0.01
White	524 (25.30)	1,417 (21.77)
Latino/Hispanic	161 (7.77)	452 (6.94)
Asian	7 (0.34)	22 (0.34)
Native American	85 (4.10)	233 (3.58)
Other	14 (0.68)	38 (0.58)
Unknown	15 (0.72)	47 (0.72)
Obese	1,141 (55.09)	3,586 (55.09)	0.99
Asthma	281 (13.57)	896 (13.77)	0.85
Diabetes	85 (4.10)	272 (4.18)	0.90
Chronic hypertension	95 (4.59)	310 (4.76)	0.76
Hypertensive disorder during pregnancy	414 (19.99)	1,317 (20.23)	0.81
Medical or antepartum complication	678 (32.74)	2,118 (32.54)	0.87
Prior cesarean section	158 (7.63)	603 (9.26)	0.02
Prior preterm birth	180 (8.69)	611 (9.39)	0.34
Nulliparity	891 (43.02)	2,780 (42.71)	0.80
Alcohol use	27 (1.30)	63 (0.97)	0.19
Tobacco use	286 (13.81)	883 (13.57)	0.78
Drug use	229 (11.06)	762 (11.71)	0.42

Abbreviations: AMA, advanced maternal age; IQR, interquartile range.

Note: Data are presented as n (%) unless otherwise noted. Values in bold denote statistical significance (p < 0.05).

There was no significant difference in the risk of the primary outcome of neonatal composite morbidity (adjusted odds ratio [aOR]: 0.99; 95% confidence interval [CI]: 0.831.18) (Table 2). There were also no differences in the components of the composite with the exception of seizure(s), which was associated with a higher risk (aOR: 2.62; 95% CI: 1.03–6.68) in neonates with an NC. All infants with seizures underwent magnetic resonance imaging (MRI) of the head, and the results were normal in 3/8 neonates with NC versus 5/10 neonates without NC. Rates of NICU admission, arterial cord pH < 7, and low 5-minute Apgar score < 7 were also similar between groups (Table 2). With regard to labor characteristics, patients with NC were more likely to receive oxytocin (aOR 1.15; 95% CI: 1.04–1.28) and have an operative vaginal delivery (OVD) (6.4 vs. 4.3%; p < 0.01; aOR 1.47; 95% CI: 1.18–1.81) and less likely to deliver by cesarean (13.4 vs. 18.1%; p < 0.01; aOR 0.73; 95% CI: 0.63–0.83) (Table 3). The most common indication for both cesarean section and OVD was nonreassuring fetal status.

Table 2.

Comparison of neonatal outcomes in the presence or absence of a nuchal cord

	Nuchal cord, N = 2,071	No nuchal cord, N = 6,509	p-Value	OR	aORa
Neonatal composite morbidity	180 (8.69)	577(8.86)	0.81	0.98 (0.82–1.17)	0.99 (0.83–1.18)
Neonatal death	2 (0.10)	2 (0.03)	0.23	3.14 (0.44–22.34)	3.34 (0.47–23.88)
Seizure	8 (0.39)	10 (0.15)	0.04	2.52 (0.99–6.39)	2.62 (1.03–6.68)
Hypoxic-ischemic encephalopathy	2 (0.10)	14 (0.22)	0.39	0.45 (0.10, 1.98)	0.43 (0.10, 1.92)
Need for hypothermic treatment	9 (0.43)	33 (0.51)	0.68	0.86 (0.41–1.79)	0.84 (0.40–1.75)
Respiratory morbidity	90 (4.35)	242 (3.72)	0.20	1.17 (0.92–1.51)	1.20 (0.94–1.54)
Hypotension requiring treatment	2 (0.10)	4 (0.06)	0.60	1.57 (0.29–8.59)	1.54 (0.28–8.47)
Suspected sepsis	144 (6.95)	483 (7.42)	0.48	0.93 (0.77–1.13)	0.94 (0.78–1.15)
NICU admission	33 (1.59)	99 (1.52)	0.83	1.05 (0.71–1.56)	1.04 (0.70–1.54)
Arterial cord pH < 7	6 (0.29)	19 (0.29)	1	0.99 (0.40–2.49)	0.95 (0.38–2.39)
5-minute Apgar < 7	57 (2.75)	151 (2.32)	0.27	1.19 (0.88–1.62)	1.22 (0.90–1.67)

Abbreviations: aOR, adjusted odds ratio; NICU, neonatal intensive care unit; OR, odds ratio.

Note: Data are presented as n (%). Values in bold denote statistical significance (p < 0.05)

^aAdjusted for maternal age, black race, and prior cesarean section.

Table 3.

Comparison of pregnancy outcomes in the presence or absence of a nuchal cord

	Nuchal cord, N = 2,071	No nuchal cord, N = 6,509	p-Value	OR	aORa
Gestational age (wk)
Early term (37–38.6)	719 (34.72)	2,332 (35.83)	0.23	Reference	Reference
Term (39–40.6)	1,185 (57.22)			1.06 (0.96–1.19)	1.05 0.94–1.17)
Late term (≥41)	167 (8.06)	3,597 (55.26) 580 (8.91)		0.93 (0.77–1.13)	0.91 (0.75–1.11)
Oxytocin use	1,437 (69.39)	4,309 (66.20)	<0.01	1.16 (1.04–1.29)	1.15 (1.04–1.28)
Epidural	1,861 (89.86)	5,822 (89.45)	0.59	1.05 (0.89–1.23)	1.09 (0.93–1.29)
Small for gestational age	318 (15.35)	929 (14.27)	0.22	1.09 (0.95–1.25)	1.13 (0.99–1.30)
Induction of labor	937 (45.24)	2,850 (43.79)	0.24	1.06 (0.96–1.17)	1.05 (0.95–1.16)
Indication for delivery
Nonreassuring fetal status	289 (13.95)	894 (13.73)	0.80	1.01 (0.88–1.18)	1.05 (0.91–1.21)
Mode of delivery
Spontaneous vaginal delivery	1,660 (80.15)	5,045 (77.51)	<0.01	Reference	Reference
Operative vaginal delivery	133 (6.42)	279 (4.29)		1.45 (1.16–1.79)	1.47 (1.18–1.81)
Cesarean delivery	278 (13.42)	1,181 (18.14)		0.71 (0.61–0.82)	0.73 (0.63–0.84)
Meconium	462 (22.31)	1,351 (20.76)	0.13	1.10 (0.97–1.24)	1.11 (0.98–1.25)

Abbreviations: aOR, adjusted odds ratio; OR, odds ratio.

Note: Data are presented as n (%). Values in bold denote statistical significance (p < 0.05).

^aAdjusted for maternal age, black race, and prior cesarean section.

We further examined the FHR characteristics in the 30 minutes prior to delivery. The presence of an NC was associated with a significant increase in repetitive late decelerations (aOR: 1.45; 95% CI: 1.12–1.87), repetitive variable decelerations (aOR: 1.41; 95% CI: 1.27–1.58), and overall category II tracings (aOR: 1.53; 95% CI: 1.38–1.70) (Table 4).

Table 4.

Fetal heart rate characteristics in 30 minutes prior to delivery in the presence or absence of a nuchal cord

	Nuchal cord, N = 2,071	No nuchal cord, N = 6,509	p-Value	OR	aORa
Baseline
>160	66 (3.19)	210 (3.23)	0.93	0.99 (0.75–1.31)	0.97 (0.73–1.29)
<110	3 (0.14)	17 (0.26)	0.44	0.55 (0.16–1.89)	0.56 (0.16–1.91)
Variability
Moderate variability	1,016 (49.06)	2,931 (45.03)	<0.01	1.18 (1.06–1.30)	1.16 (1.05–1.28)
Marked variability	2 (0.10)	9 (0.14)	>0.99	0.70 (0.15–3.23)	0.75 (0.16–3.46)
Absent variability	0	1 (0.02)	>0.99	–	–
Accelerations/decelerations
Repetitive late decelerations	91 (4.40)	193 (2.97)	<0.01	1.45 (1.13–1.88)	1.45 (1.12–1.87)
Repetitive variable decelerations	696 (33.61)	1,671 (25.67)	<0.01	1.42 (1.27–1.58)	1.41 (1.27–1.58)
Repetitive prolonged decelerations	43 (2.08)	109 (1.67)	0.31	1.20 (0.84–1.72)	1.20 (0.84–1.71)
Category
1	35 (1.69)	185 (2.84)	<0.01	0.59 (0.41–0.85)	0.58 (0.40–0.83)
2	1,410 (68.08)	3,772 (57.95)	<0.01	1.54 (1.39–1.72)	1.53 (1.38–1.70)
3	0	1 (0.02)	>0.99	–	–

Abbreviations: aOR, adjusted odds ratio; OR, odds ratio.

Note: Data are presented as n (%). Values in bold denote statistical significance (p < 0.05).

^aAdjusted for maternal age, black race, and prior cesarean section.

Among patients with an OVD, those with an NC were more than twice as likely (aOR: 2.40; 95% CI: 1.14–5.02) to have repetitive late decelerations, but the rates of repetitive variable decelerations were similar in the presence or absence of an NC (Table 5).

Table 5.

Fetal heart rate characteristics in 30 minutes prior to delivery in the presence or absence of a nuchal cord among patients with an operative vaginal delivery

	Nuchal cord, N = 133	No nuchal cord, N = 279	p-Value	OR	aORa
Repetitive late decelerations	16 (12.03)	15 (5.38)	0.02	2.40 (1.16–5.02)	2.40 (1.14–5.02)
Repetitive variable decelerations	47 (35.34)	78 (27.96)	0.14	1.40 (0.90–2.19)	1.42 (0.91–2.22)

Abbreviations: aOR, adjusted odds ratio; OR, odds ratio.

Note: Data are presented as n (%). Values in bold denote statistical significance (p < 0.05).

^aAdjusted for maternal age, black race, and prior cesarean section.

Discussion

Our study demonstrates that NC at delivery is common and associated with category II EFM parameters and higher rates of OVD in infants at or beyond 37 weeks. However, there is no significant association between NC and neonatal morbidity; thus, reassurance can be provided to parents when NC is diagnosed and there is likely no utility for NC screening.

Previous literature has shown opposing results regarding the significance of an NC. In some reports, presence of an NC has been associated with poor neonatal outcomes including unexplained quadriplegia,²⁸ fetal distress, birth asphyxia, and neonatal death.²⁹ Several small retrospective studies found NC to be associated with increased rates of nonreassuring FHR patterns (variable decelerations, fetal bradycardia), meconium-stained amniotic fluid, operative delivery, and acidic umbilical artery pH.^{1,8,10,13,16–18} In general, however, the majority of previous studies have found no increase in the risk of neonatal morbidity associated with NC at delivery.^3,7

The results of this study are in agreement with the suggestion that there is no significant risk of neonatal morbidity when an NC is present at delivery. Furthermore, in contrast to many earlier studies, our large study did not find any significant association with neonatal death, cord acidosis, birth weight, low Apgar score, NICU admission, or respiratory morbidity.

A unique component of this study is the inclusion of EFM data and its relation to neonatal morbidity. Few prior studies have evaluated the characteristics of EFM that are associated with NC at delivery. Peregrine et al found no association between NC and abnormal EFM parameters.³⁰ In contrast, Sheiner et al reported that nonreassuring EFM patterns are associated with NC.³ Our study found significant associations with NC and category II EFM parameters. However, the lack of significant neonatal outcomes and interventions associated with an NC calls into question whether its association with nonreassuring FHR patterns is clinically relevant. Our results suggest that the higher rates of OVD in the NC group were in response to category II EFM. Therefore, it is possible that this intervention improved the rates of neonatal morbidity in the NC group.

Multiple factors support the validity of our study. Prospective interpretation of FHR tracings by nurses who are blinded to clinical outcome is a major strength. Additionally, to the best of our knowledge, this is the largest prospective study to date of patients with an NC at delivery. Our EFM analysis was limited to the final 30 minutes prior to delivery since the impact of an NC is most likely to be experienced during the second stage of labor with the descent of the fetus. Limiting our patient population to women reaching the second stage and the final 30 minutes of monitoring helped us discriminate between variables most likely caused by an NC versus other sources.

Given the large sample size and small amount of missing data, due to our prospective study design, findings can be applied widely and support the generalizability of our findings.

Despite strengths, this study has some potential limitations to be considered when evaluating our results. As with all cohort studies, confounding is a concern. We used appropriate statistical techniques to adjust for confounders, but there is a possibility of residual confounding by unmeasured factors. For example, the presence of nuchal is not routinely noted on ultrasound reports at our institution. However, we do not know whether clinicians managing labor had knowledge regarding the presence of an NC by bedside ultrasound prior to delivery and, if so, whether this knowledge altered management. It is also possible that neonatal outcomes were similar between groups because there was a higher level of intervention, such as OVD in the NC group in response to category II EFM parameters or an undefined aspect of the clinical picture. Our findings may not be generalizable to other hospital settings since we are a regional referral center with a high level of acuity due to a significant chronic disease burden in our patient population and a robust transport service, which drives our high rate of medically indicated labor induction. Additionally, we did not differentiate the number of times the NC was wrapped around the neonate’s neck. Some prior studies found significant neonatal risk associated specifically with a tight or multiple NC.

The use of a composite outcome may be viewed as a limitation of this study. However, we believe that the use of a composite was necessary because the individual components of the composite are rare complications. In addition, the neonatal outcomes that were considered as part of the composite are more clinically meaningful than more commonly occurring surrogate measures of morbidity, such as low Apgar score, but they are short term, and we are unable to comment on any long-term sequelae of NC at the time of delivery.

In summary, NC at delivery is associated with category II EFM parameters, which likely influences provider behaviors and increases the likelihood for OVD. Fortunately, concerning EFM patterns do not translate into fetal compromise—either because the NC is innocuous or clinical practice patterns cause providers to intervene before fetal compromise occurs in the second stage. Either way, parents and providers alike can be reassured that there is no significant association between NC and short-term neonatal morbidity within the context of current obstetric practice patterns.