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ORIGINAL RESEARCH |
From the Department of Obstetrics, University Hospital Zürich, Zürich, Switzerland.
Address reprint requests to: Address correspondence to: Dr. Leonhard Schäffer, Universitäts-Frauenklinik, Frauenklinikstrasse 10, CH-8091 Zürich, Switzerland; e-mail: leonhard.schaeffer{at}usz.ch.
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ABSTRACT |
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Methods: A total of 11,748 women with planned vaginal deliveries, including 9,574 term and 2,174 postterm deliveries, were analyzed for intrapartum events, clinical peripartum management, mode of delivery, and neonatal outcome. The presence of nuchal cords was diagnosed clinically at the time of delivery. Data were obtained from our perinatal database between 1995 and 2004 for retrospective analysis.
Results: The incidence of nuchal cords in term and postterm deliveries was 33.7% and 35.1%, respectively. Multiple nuchal cords were present in 5.8% of term and 5.5% of postterm deliveries. Intrapartum signs of fetal compromise were increased in all groups, albeit not all reaching statistical significance in postterm deliveries. Meconium staining was significantly increased only in multiple nuchal cords of postterm deliveries (42.1% compared with 30.1%, P < .05). Mode of delivery was unchanged in all nuchal cord groups. Unfavorable neonatal blood gas values were significantly more frequent in all nuchal cord groups. Nevertheless, 5-minute Apgar scores less than 7 were not more common, and admission to neonatal unit was not required more frequently. Neonatal mean birth weight was significantly lower in all nuchal cord groups.
Conclusion: Nuchal cords do not influence clinical management at delivery, and neonatal primary adaption is not impaired. Our data show that ultrasonographic nuchal cord assessment is not necessary at the time of admission for delivery.
Level of Evidence: II-3
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MATERIALS AND METHODS |
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Fetal heart rate was monitored routinely during the active phase of labor and was defined as being not reassuring when severe variable or recurrent late decelerations, loss of beat-to-beat variability, bradycardia or tachycardia were present according to an American College of Obstetricians and Gynecologists Technical Bulletin.10
As measure for normal or abnormal cord blood gas values, 5th or 95th percentiles, respectively, of normal values were used.11 Accordingly, cutoff values of umbilical arterial cord blood of fetuses with Apgar scores of 7 or greater at 5 minutes were the following: 5th percentile of umbilical arterial Po2: 1.1 kPa, 95th percentile of umbilical arterial Pco2: 9.2 kPa, 5th percentile of umbilical arterial base excess: –10 mmol/L.
All statistical analyses were performed with STATA 7 Statistics/Data Analysis Software (Stata Corporation, College Station, TX) according to Altman's recommendations,12 using Pearson’s 
2 test for comparisons of frequencies and Student t test for group comparisons. Odds ratios (ORs) with 95% confidence intervals were calculated. Subsequent to the univariate analysis, multivariate logistic regression was performed to evaluate the effect of variables such as the presence of nuchal cords, term or postterm delivery, and mode of delivery in relation to the major outcome variables such as 5-minute Apgar less than 7, umbilical artery pH less than 7.1, and referral to neonatal unit. Each logistic regression model was tested for goodness-of-fit, applying the Hosmer and Lemeshow test.13 Odds ratios were adjusted for birth weight. All differences were defined as being statistically significant at P < .05.
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RESULTS |
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To evaluate signs of fetal compromise related to nuchal cords and their potential effect on clinical management intrapartum, we analyzed fetal heart rate patterns during first and second stages of labor and signs of meconium-stained amniotic fluid as tools for fetal monitoring. As features of clinical management, we analyzed mode of delivery, use of episiotomy, and duration of second stage of labor (Table 2).
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In all nuchal cord groups, cardiotocography tracings were more likely to show nonreassuring fetal heart rate patterns during the first and second stages of labor than in controls, albeit not reaching statistical significance in overall nuchal cords in first stage (P = .069) and multiple nuchal cords in second stage (P = .250) of labor in postterm pregnancies. Nevertheless, presence of meconium-stained amniotic fluid was markedly increased in postterm multiple cords only (42.1% compared with. 30.1%, P < .05). Use of episiotomy was significantly increased in term nuchal cord groups, but not in the postterm subgroups. Despite these findings, neither the rate of vaginal operative deliveries nor the rate of deliveries by cesarean were significantly increased in any nuchal cord group in term and postterm deliveries. Furthermore, duration of second stage of labor was unchanged.
Neonatal outcome was analyzed by laboratory measures as markers for fetal intrapartum asphyxia and by clinical measures for evident neonatal compromise (Table 3). Values of arterial pH less than 7.1, Po2 less than 1.1 kPa (5th percentile), Pco2 more than 9.2 kPa (95th percentile), and base excess less than 10 mmol/L were markedly more frequent in neonates of all nuchal cord groups, albeit base excess in postterm overall nuchal cords did not reach statistical significance (P = .160).
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Consistent with laboratory measures, neonates with low 1-minute Apgar scores (< 7) were found significantly more frequently in all umbilical cord groups. Nevertheless, low 5-minute Apgar scores (< 7) were not more common in the nuchal cord groups, and admission to neonatal unit was not required more frequently compared with absent nuchal cord of either term or postterm pregnancies.
To search for evidence of potentially prolonged existence of nuchal cords, we analyzed neonatal mean birth weight. We found significantly lower birth weights in all nuchal cord groups. This was especially pronounced in multiple cords, with a decrease of 93 g in term and 180 g in postterm multiple nuchal cords (P < .05).
To identify the influence of selected confounding variables on major outcome variables, multivariate logistic regression analysis was performed. As shown in Table 4, umbilical artery pH less than 7.1 was significantly influenced by all variables assessed with highest odds ratio for the presence of nuchal cords (OR 1.81). The presence of 5-minute Apgar less than 7 was significantly influenced only by mode of delivery, with an odds ratio of 4.3 for secondary cesarean delivery. Referral to neonatal unit was again mostly influenced by mode of delivery (OR 2.03 for forceps or vacuum, OR 3.16 for cesarean delivery).
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DISCUSSION |
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Interestingly, although fetal heart rate tracings as a primary measure of fetal condition was more frequently abnormal in all nuchal cord groups, clinical management reflected by mode of delivery was not significantly changed. This was also true for postterm deliveries, which additionally displayed a significant increase of 40% in meconium-stained amniotic fluid in multiple cords. Only use of episiotomy was significantly increased in both nuchal cord subgroups in term but not postterm deliveries, from 47.1% to 51.6% and 51.8%, respectively. The lack of increase in postterm deliveries may be explained by the overall higher incidence of episiotomies in pregnancies without nuchal cords, probably due to the overall increased mean birth weight in these pregnancies.
Our results are in contrast to Larson et al,1 who found a significant increase in vaginal operative deliveries of 55% in 326 multiple nuchal cord pregnancies, but not in the rate of cesarean deliveries. Furthermore, Jauniaux et al2 found a doubling in the rate of cesarean deliveries in multiple nuchal cords from 5.3% to 12.5%. The reason for these different results may be explained by different distributions of numbers of nuchal cords or due to different management procedures on site. Also, the significant increase in meconium-stained amniotic fluid in nuchal cords in those studies may have influenced decision making. Nevertheless, the overall incidence of umbilical artery pH less than 7.1 in our population, although significantly increased in term and postterm deliveries of all nuchal cord groups, was still lower in all groups of term deliveries compared with the study of Larson,1 and duration of second stage of labor was not significantly prolonged. However, multivariate logistic regression identified mode of delivery and gestational age as additional independent variables significantly influencing umbilical artery pH.
To further characterize neonatal acidemia, blood gases (Po2, Pco2) as markers for respiratory acidemia and base excess as metabolic measure were analyzed, which revealed a marked increase in all measures, especially in multiple nuchal cords of both term and postterm deliveries. These results may reflect the increase in low 1-minute Apgar values in all nuchal cord groups. Nevertheless, the multiple incidence of unfavorable blood gas values compared with low base excess values and the presence of normal 5-minute Apgar scores in nuchal cords may point to a primarily respiratory or mixed acidemia with fast equilibration. This is supported by Hankins et al,14 who found in 110 term deliveries with nuchal cord mixed acidemia in 68% and acidemia of pure respiratory incidence in 23%. Normal 5-minute Apgar levels in single and multiple nuchal cords have been shown previously. We expand these findings to postterm pregnancies which likewise do not show a significant increase in problems of primary neonatal adaptation. As expected, multivariable analyses revealed mode of delivery as major confounder for a low Apgar level, reflecting the necessity for rapid delivery in these cases. To confirm these results, the incidence of referral to the neonatal unit was analyzed, which did not show any significant increase in neonatal admission of children with nuchal cords of term and postterm deliveries. Again, mode of delivery was major confounder. Thus, primary clinical evaluation did not reveal a higher incidence of fetal compromise in nuchal cords either. These results are in line with the study of Miser 1992,3 who found despite a significant increase in unfavorable heart rate patterns no significant difference in Apgar scores at 1 and 5 minutes between the two groups. In contrast, Jauniaux2 found a significant increase in admission of neonates to the intensive care unit as well as an increase in neonatal resuscitation. Surprisingly, in this study the rates of 5-minute and 10-minute Apgar scores less than 7 were not significantly increased in nuchal cords. Nevertheless, the percentage of intensive care unit admissions in this population was 6.2% in normal deliveries, 10% in all nuchal cords, and 14% in multiple cords, which is comparatively high compared with our data. Stornes15 did not find a significant association between 5-minute Apgar scores and the number of nuchal cords. In that study, the relative influence of nuchal cords compared with fetal growth restriction on fetal outcome was analyzed, revealing that poor fetal outcome was due to the accompanying level of growth restriction and not due to the presence of nuchal cord. An association between umbilical cords and fetal weight decrease has been described repeatedly.3,6,7 Our data reveal that fetal weight decrease associated with nuchal cords is, although significant in all groups, especially pronounced in postterm deliveries with multiple cords. Although the reduction in fetal birth weight attributed to nuchal cord problems may not account for complications related to growth restriction by clinical means, it still may reflect the result of prolonged nuchal cord existence, especially in multiple cords with fetuses potentially suffering from compromised umbilical circulation. This assumption is supported by several studies, which showed persistent cerebral vasodilation, mild asymmetric growth restrictions, and laboratory measures as evidence of chronic mild intrauterine fetal hypoxia, especially in tight or multiple cords at delivery resulting in at least subclinical deficits in neurodevelopmental performance at 1 year of age.
Nuchal cords at term can be identified ultrasonographically with high sensitivity and specificity, especially using color flow Doppler imaging.2,19,20 The incidence of nuchal cords has been shown to rise with advancing gestation.17 Although the majority of nuchal cords seem to be transient events, in cases of prolonged persistence, increased risks for fetal compromise has been suspected.17 The finding of markedly decreased fetal weights in multiple cords therefore may be indicative of a prolonged nuchal cord persistence, leading to chronic mild fetal hypoxia. This may explain the finding of significant increase in meconium-stained amniotic fluid in postterm pregnancies. Therefore, even though nuchal cords are not relevant for delivery procedures, they may have an effect on setting the optimal time for delivery. Accordingly, in women not delivering at term, it might be reasonable to scan for multiple nuchal cords at routine term assessment and, if present, to discuss induction of labor to prevent mature fetuses from experiencing potentially harmful persistent nuchal cords. However, management of prenatally found nuchal cords and the effect on the fetus during the ongoing pregnancy was not analyzed in the present study, and optimal management is under debate.21 Prenatal ultrasound assessment of nuchal cords at short-term intervals to confirm prolonged nuchal cord persistence in multiple cords and long-term studies on fetal neurodevelopmental outcome in these cases must clarify whether such considerations can be justified.
In summary, nuchal cords at delivery of term and postterm pregnancies do not alter clinical management despite increased intrapartum signs of fetal compromise. Furthermore, primary adaptation of neonates with nuchal cords is not impaired. Therefore, at the time of admission for delivery, ultrasound assessment for nuchal cords is not a useful procedure.
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Footnotes |
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doi:10.1097/01.AOG.0000165322.42051.0f
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REFERENCES |
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2. Jauniaux E, Ramsay B, Peellaerts C, Scholler Y. Perinatal features of pregnancies complicated by nuchal cord. Am J Perinatol 1995;12:255–8.[Medline]
3. Miser WF. Outcome of infants born with nuchal cords. J Fam Pract 1992;34:441–5.[Medline]
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10. American College of Obstetricians and Gynecologists. Intrapartum fetal heart rate monitoring: guidelines for monitoring, terminology, and instrumentation. ACOG Technical Bulletin 132. Washington, DC: ACOG; 1989.
11. Helwig JT, Parer JT, Kilpatrick SJ, Laros RK Jr. Umbilical cord blood acid-base state: what is normal? Am J Obstet Gynecol 1996;174:1807–12.[Medline]
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14. Hankins GD, Snyder RR, Hauth JC, Gilstrap LC 3rd, Hammond T. Nuchal cords and neonatal outcome. Obstet Gynecol 1987;70:687–91.[Abstract]
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18. Hashimoto K, Clapp JF. The effect of nuchal cord on amniotic fluid and cord blood erythropoietin at delivery. J Soc Gynecol Investig 2003;10:406–11.[Medline]
19. Qin Y, Wang CC, Lau TK, Rogers MS. Color ultrasonography: a useful technique in the identification of nuchal cord during labor. Ultrasound Obstet Gynecol 2000;15:413–7.[Medline]
20. Funk A, Heyl W, Rother R, Winkler M, Rath W. Subpartal diagnosis of umbilical cord encirclement using color-coded Doppler ultrasonography and correlation with cardiotocographic changes during labor [in German]. Geburtshilfe Frauenheilkd 1995;55:623–7.[Medline]
21. Sherer DM, Manning FA. Prenatal ultrasonographic diagnosis of nuchal cord(s): disregard, inform, monitor or intervene? Ultrasound Obstet Gynecol 1999;14:1–8.[Medline]
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