Do fetal heart rate deceleration patterns during labor

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Feb 6, 2009 - Methods: Vertex singleton cases with nuchal cord (226 cases), velamentous (12 cases), marginal cord insertion. (53 cases) or hyper-coiled ...
Article in press - uncorrected proof J. Perinat. Med. 37 (2009) 276–280 • Copyright  by Walter de Gruyter • Berlin • New York. DOI 10.1515/JPM.2009.039

Do fetal heart rate deceleration patterns during labor differ between various umbilical cord abnormalities?* Junichi Hasegawa**, Ryu Matsuoka, Kiyotake Ichizuka, Masamitsu Nakamura, Akihiko Sekizawa and Takashi Okai Department of Obstetrics and Gynecology, Showa University School of Medicine, Tokyo, Japan

Abstract Objective: To examine differences in intrapartum fetal heart rate (FHR) patterns among cases with various cord abnormalities. Methods: Vertex singleton cases with nuchal cord (226 cases), velamentous (12 cases), marginal cord insertion (53 cases) or hyper-coiled cord (39 cases) and without them (466) that were delivered at our hospital were examined. The relationship between cord abnormalities and intrapartum FHR patterns were retrospectively investigated. Deceleration patterns were analyzed for the presence of variable, early, late and prolonged decelerations. The frequencies of each FHR pattern per uterine contraction were assessed during 30 uterine contractions at the end of the first stage and throughout the entire second stage of labor. Results: In the first stage of labor, frequencies of variable decelerations were 34.5"23.8% and 27.3"25.5% in cases with velamentous insertion and hyper-coiled cord, respectively. These were significantly higher than in controls (11.7"17.3%, P-0.0001). In the second stage of labor, however, frequencies of each deceleration were not different among various cord abnormalities. Conclusion: Fetal heart rate tracing from the first stage of labor is indicated in cases with the prenatal diagnosis of velamentous insertion or hyper-coiling of the cord. Keywords: Cardiotochogram; fetal heart rate; hypercoiled cord; nuchal cord; variable deceleration; velamentous cord insertion. *Source of funding: This study was supported in part by Grantsin-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture of Japan (No. 80365775). **Corresponding author: Dr. Junichi Hasegawa, MD, PhD, Department of Obstetrics and Gynecology Showa University School of Medicine 1-5-8 Hatanodai Shinagawa-ku Tokyo, 142-8666 Japan Tel.: q81-3-3784-8551 Fax: q81-3-3784-8355 E-mail: [email protected]

Introduction With the improvement of ultrasound technology, the detection rate of umbilical cord abnormalities is steadily increasing. Although ultrasound scanning might distinguish umbilical cord conditions, this information did not have much impact on management of labor. Currently, fetal well-being during labor is established solely by fetal heart rate (FHR) tracing. The decision to proceed with a cesarean delivery because of fetal distress is based on factors such as subjective interpretation of the FHR tracing and, in many institutions, on fetal blood sampling. The predictivity of FHR patterns is difficult to quantify because different methods are used for interpretation and different durations of time are used for assessment of various monitoring parameters. One FHR parameter assessed is bradycardia, or a prolonged deceleration, which leads to immediate operative delivery in such cases where the FHR pattern does not recover despite injection of tocholytic agent or the change of maternal position; however, many of these infants are delivered with normal Apgar score and without evidence of acidosis. Immediate intervention in every patient with a fetal bradycardia would lead to an increased operative delivery rate; many of these deliveries would be uncompromised infants whose mothers would have an increased risk of intrapartum trauma w22x. Therefore, it may be necessary to manage labor considering the complication or abnormalities of the cord and the placenta before a final decision for cesarean delivery is made. A previous study recommended that antenatal detection of cord abnormalities with ultrasonography may be helpful in selective cases in which strict fetal monitoring is warranted, before as well as during labor w5x. Then, it is considered that clarifying relations between umbilical cord abnormalities and intrapartum FHR patterns may improve outcomes of deliveries. In the present study, we examined intrapartum FHR patterns in the presence of umbilical cord abnormalities which have long been associated with non-reassuring fetal status (NRFS) and cesarean section w6, 7, 10, 18, 20, 21x, including velamentous cord insertions (VCIs), marginal cord insertions (MCIs), hyper-coiled cords (HCCs) and nuchal cords (NCs) in order to know whether these abnormalities have characteristic FHR deceleration patterns.

Materials and methods We performed a cohort study on differences of FHR deceleration patterns during labor between various umbilical cord abnormal

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ities. Consecutive vertex singleton cases with and without cord abnormalities, which were delivered between 37 and 41 weeks’ gestation at Showa University Hospital from June 2005 to December 2006, were retrospectively reviewed. Cord abnormalities included MCIs, VCIs, HCCs and NCs.

Diagnosis of cord abnormalities In our institution, all placentas, umbilical cords and membranes were intimately examined by obstetricians, and detailed data were stored in medical records. Definitions of umbilical cord abnormalities are as follows. 1) Abnormal Cord Insertion: after delivery, the placenta and the umbilical cord were examined. VCI is an abnormal cord insertion (CI) in which the umbilical vessels diverge as they traverse between the amnion and chorion before reaching the placenta. MCI was defined as CI was located on the placenta 1 cm or less from placental edge. 2) Hyper-coiled cord (HCC): this diagnosis was made at birth. The umbilical coiling index was calculated by dividing the total number of coils by the length of the cord in centimeters. HCC is defined in cases of umbilical coiling index G0.3 coils/ cm w21x. 3) Nuchal cord (NC): NC was diagnosed at birth. All cases were classified as no NC, one NC, or two or more NCs. In intrapartum FHR observation, NRFS was diagnosed when severe variable decelerations (VDs), prolonged decelerations (PDs), recurrent late decelerations (LDs), diminished baseline variability, or fetal bradycardia occurred. In the second stage of labor, vacuum extractions and forceps deliveries at lower stations were performed because of NRFS or failure to progress. In the first stage of labor, emergency cesarean sections were performed because of NRFS, major vaginal hemorrhage, or failure to progress. Regardless of an antenatal ultrasound diagnosis of cord abnormalities, management of delivery was conducted in accordance with the aforementioned NRFS definitions.

FHR analysis FHR deceleration patterns were analyzed for 30 uterine contractions from the end of first stage through the entire second stage of labor. In the analysis of emergency cesarean cases, deceleration patterns were examined for 30 uterine contractions before operation. FHR patterns were analyzed for the presence of VDs, early decelerations (EDs), LDs and PDs. The National Institute of Child Health and Human Development (NICHD) w1x guidelines were applied for FHR interpretation. The FHR patterns in each case were carefully examined for uterine contractions. The frequencies of each FHR pattern per uterine contraction were assessed from the end of the first through the second stage of labor. FHR interpretation was blinded to the neonatal outcome.

Definitions of decelerations The decreases in heart rates were calculated from the most recently determined portion of the baseline. 1) Variable Deceleration (VD): defined as a visually apparent abrupt decrease (onset of deceleration to beginning of nadir -30 s) in FHR below baseline. The decrease in FHR below

baseline was G15 beats/min, lasting F2 min from onset until return to baseline. 2) Early Deceleration (ED): a visually apparent gradual (defined as onset of deceleration to nadir G30 s) decrease and return to baseline associated with a uterine contraction. It is coincident with the nadir of the deceleration occurring at the same time as the peak of the contraction. 3) Late Deceleration (LD): a visually apparent gradual (onset of deceleration to nadir G30 s) decrease and return to baseline associated with uterine contraction. The deceleration is delayed in timing, with the nadir of the deceleration occurring after the peak of the contraction. 4) Prolonged Deceleration (PD): a visually apparent decrease in FHR below baseline. The decrease from baseline is G15 bpm, lasting G2 min, but -10 min from onset to return to baseline.

Statistics The frequency of each FHR pattern per uterine contraction in cases with and without cord abnormalities were assessed. The data were entered into a computerized data analysis program (StatView for Windows, SAS Institute, Inc., Cary, NC). Continuous variables were compared using independent sample t-test for means. Categorical variables were reported as percentages and compared using the x2-test. Multiple comparisons were performed by analysis of variance and the Bonferroni post-hoc test. Statistical significance was defined as a P-0.05.

Results During the study period, we delivered 1229 singleton between 37 and 41 weeks’ gestation. In these pregnancies, 1081 cases were delivered vaginally and 148 cases (12.0%) were delivered by cesarean section. Out of 148 cases, 111 cases were elective and 37 were emergent cases. Elective cesarean sections were performed before the onset of labor because of previous cesarean delivery, preeclampsia, breech presentation, fetal growth restriction, vasa previa, NRFS before onset of labor or maternal complications; and emergency operations were performed due to NRFS, major vaginal hemorrhage, or failure to progress. A total of 736 vaginal births and 26 cesarean cases of FHR records which were interpretable and perfectly fulfilled the condition mentioned in the methods section after 37 weeks’ gestation were presented and analyzed. In all 762 analyzed cases, cases with and without cord abnormalities were 296 and 466. The 296 abnormal cord cases included 53 MCI, 12 VCI, 39 HCC and 226 NC cases (including multiple cord abnormalities). Maternal and neonatal demographics are presented in Table 1. Frequency of vacuum extraction or forceps delivery was higher in VCI cases than in controls. Frequency of emergency cesarean section was higher in HCC cases than in controls. The frequency of each deceleration per uterine contraction stratified by cord factors is presented in Table 2.

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Table 1 Maternal and neonatal demographics.

Age (years) Delivery (weeks) Para (median) Birth weight (g) Apgar score (median)1/5 min UA pH Normal delivery Forceps/vacuum Emergency CS

Control

Cord abnormalities

466 (61.2%)

296 (38.8%)

MCI 53 (7.0%)

VCI 12 (1.6%)

HCC 39 (5.1%)

NC 226 (29.7%)

32.7"5.2 39.1"1.0 1 3030"356 9/9

32.0"4.9 39.3"1.0 0 3026"369 9/9

32.7"4.3 39.1"1.1 0 2867"315 9/9

33.0"3.5 39.6"1.0 0 3184"270 8.5/9.5

32.7"4.8 39.5"1.1 0 3066"481 9/9

31.9"5.1 39.3"1.0 0 3046"355 9/9

7.32"0.07 423 23 15

7.31"0.07* 261 24 11

7.32"0.07 44** 7 2

7.33"0.05 9 2** 1

7.29"0.10* 32 3 4**

7.31"0.07* 203 17 6

Data indicate percent or mean"standard deviation. Cases with multiplicity of cord abnormalities are included. MCI, marginal cord insertion; VCI, velamentous cord insertion; HCC, hyper coiled cord; NC, Nuchal cord; UA, umbilical artery. *Between control and total cord abnormalities, P-0.05 using the t-test. **Between control and each cord abnormalities, P-0.05 using the x2-test.

Table 2 Frequencies of decelerations per uterine contraction in end of first stage and second stage of labor stratified cord abnormalities. First stage

Control

Cord abnormalities

(466)

(296)

MCI (53)

VCI (12)

HCC (39)

NC (220)

ED VD LD PD

1.4"5.1 11.7"17.3 0.7"3.5 0.9"3.3

2.2"7.0 21.0"23.8* 0.6"2.3 1.3"3.7*

1.0"3.4 17.6"23.1 0.1"0.5 1.2"3.5

1.7"2.8 34.5"23.8** 1.2"3.5 1.8"3.1

2.0"4.8 27.3"25.5** 0.5"2.0 1.5"3.3

2.4"7.6 20.2"22.8** 0.7"2.5 1.3"3.6

Second stage

Control

Cord abnormalities

(451)

(285)

MCI (51)

VCI (11)

HCC (35)

NC (220)

1.0"4.3 46.7"34.5 0.7"3.3 12.6"24.5

1.7"5.5 44.2"33.6 1.5"5.9* 14.4"25.9

0.4"1.6 45.0"33.9 1.4"3.8 12.0"25.7

1.7"3.1 69.5"26.2 2.9"9.0 12.0"16.8

2.6"6.8 52.9"33.0 1.4"5.2 19.3"26.7

1.7"5.7 48.7"33.9 1.7"6.4 14.7"26.7

ED VD LD PD

Data indicate percent of FHR decelerations for contractions (mean"standard deviation). ED, early deceleration; LD, plate deceleration; VD, variable deceleration; PD, prolonged deceleration; MCI, marginal cord insertion; VCI, velamentous cord insertion; HCC, hyper coiled cord; NC, Nuchal cord. *Between control and total cord abnormalities. P-0.05 using the t-test. **P-0.0001 using analysis of variance; between control and each cord abnormalities, P-0.0001 using the Bonferroni post-hoc test.

First, comparisons between total cord abnormalities and controls were made. The frequency of VDs in the first stage of labor was significantly higher than that of the controls (P-0.05). The frequencies of EDs and LDs in the second stage were significantly higher than those of the controls (P-0.01). Second, comparisons among various cord abnormalities were made. The frequencies of VDs in the first stage were 34.5"23.8% in VCI cases, 27.3"25.5% in HCC cases and 20.2"22.8% in NC cases. In these cases, the frequencies of VDs were significantly higher than in controls (11.7"17.3%; P-0.0001). The relationship between frequency of decelerations per uterine contraction and number of cord abnormalities found in one case is presented in Table 3. In cases with single or multiple cord abnormalities, VDs frequently

occurred in the first stage and LDs frequently occurred in the second stage of labor (P-0.0001).

Discussion VDs are most frequently observed as a type of periodic change in FHR monitoring, appearing in approximately 30% of all labors w3, 15x. Temporary cord occlusion is a likely cause of many VDs. Cord occlusion, either partial or complete, can cause both increases in after load and decreases in fetal arterial oxygen content, both of which will result in an activated vagal reflex causing bradycardia w2x. In our cases with each cord abnormality, VDs frequently appeared from the first stage of labor and instrumental

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Table 3 Relations between frequency of decelerations and number of cord abnormalities. Number of abnormalities

Number of cases

ED (%)

VD (%)

LD (%)

PD (%)

First stage of labor 0 1 G2

466 263 33

1.4"5.1 2.3"7.3 1.3"3.5

11.8"17.3 20.8"24.3* 21.8"20.2*

0.7"3.5 0.6"2.3 0.5"2.2

0.9"3.3 1.4"3.7 0.9"2.9

Second stage of labor 0 1 G2

451 254 31

1.0"4.3 1.8"5.8 0.8"2.4

46.9"34.5 48.8"33.5 54.0"33.8

0.7"3.3 1.5"5.9* 1.0"2.2*

12.6"24.5 14.2"25.4 15.0"29.4

Data indicate percent of FHR decelerations for contractions (mean"standard deviation). ED, early deceleration; LD, late deceleration; VD, variable deceleration; PD, prolonged deceleration. *P-0.0001 using analysis of variance; between cases without cord abnormality and cases with single or multiple cord abnormalities, P-0.0001 using the Bonferroni post-hoc test.

deliveries or emergency cesarean sections were frequently performed. Moreover, the frequency of VDs was high in cases with multiple cord abnormalities. Clark reported a case of VCI in which VDs occurred despite intact membranes and minimal evidence of uterine contractions w4x. In VCI cases, the cause of frequent VDs and VDs from early labor are probably due to compression of aberrant vessels, which are not coated or thinly coated with Wharton’s jelly, and that the blood flow of both the umbilical arteries and vein would be obstructed at the same time during uterine contractions or fetal movement. In the present study, particularly in VCI cases, VDs were significantly higher in the first stage of labor. One obvious benefit of a coiled cord is its enhanced capacity to withstand kinking, compression and torsion, which can be demonstrated in a telephone cord w5x. Increased coiling is associated with a pulsatile pattern of the umbilical venous flow velocity waveform similar to that seen with abnormalities of the fetal central venous flow secondary to severe circulatory compromise w12, 13x. These findings suggest that HCC may result in compression of the umbilical vein and consequent compromise of the placento-fetal blood flow. It is likely that HCCs are less flexible or more prone to kinking and torsion during labor w17, 21x, leading to fetal hypoxia w7x. The result of the present study showing high frequency of VDs in the first stage suggests such events as kinking may likely occur early in labor. A higher rate of NRFS was noted among pregnancies with NC than that of the control group (ORs1.8; 95% CI: 1.6–1.9) w19x. Ogueh et al. w14x reported that the proportion of abnormal FHR patterns was also higher with the presence of a NC, particularly a tight NC (adjusted OR 1.61, 95% CI: 1.55–1.68 for all NC; adjusted OR 1.79, 95% CI: 1.66–1.94 for tight NC). In our NC cases, VDs occurred frequently in the first stage, though normal delivery rate was similar to controls. It appears that various factors influence the impact of a NC, including frequency and intensity of entanglements on appearance of VDs, but it does not necessarily indicate fetal compromise.

A previous study reported that cord problems are statistically significant factors associated with abnormal FHR tracings during the second stage of labor (ORs1.8 95%; CI: 1.03–3.3; P-0.042) w18x. Conversely, Ball et al. concluded that second stage decelerations are probably from dural pressure or fetal cerebral hypoxia, causing a vagal response mediated through chemoreceptors and baroreceptors w2x. Controversy exists in the literature regarding the ability of abnormal FHR patterns during the second stage of labor to predict fetal compromise w18x. Several studies found that abnormal FHR patterns during the second stage were significantly associated with low Apgar scores and a cord pH-7.2 w8, 9, 11, 16x. In our study, cases with cord abnormalities have high frequency of LDs in the second stage of labor, and LDs were more common in the cases with multiple abnormalities. However, even in cases without cord abnormality, VDs occurred frequently in the second stage; this finding is not only due to cord compression but also to significant head compression. Head compression causes a vagal discharge due to dural stimulation. This vagal discharge results in bradycardia w2x. During the second stage, the fact that a significant difference from control was found in the frequency of LDs but not in the frequency of VDs might be due to the following: high incidence of decelerations in the second stage of labor is readily explained by the associated fetal descent that leads to fetal head and umbilical cord compression; and the frequent occurrence of LDs in the final phase of labor reflects insufficient oxygenation of fetal blood as a consequence of high intravillous space pressures during the time of relative uterine hypertonicity w11x. Sheiner et al. reported monitor patterns found to be associated with fetal acidosis were LDs, bradycardia -70 bpm in the second stage of labor, and/or the presence of abnormal FHR patterns during the first stage w18x. Our results also showed the same phenomenon in cases with cord abnormalities. We suggest that these findings call for intensive fetal heart rate monitoring from the first stage of labor. We particularly recommend that cases with VCI

Article in press - uncorrected proof 280 Hasegawa et al., FHR in umbilical cord abnormalities

or HCC should have careful FHR monitoring from the first stage of labor.

Acknowledgements This study was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture of Japan (No. 80365775). We wish to thank Prof. Yuji Kiuchi (Department of Pathophysiology School of Pharmaceutical Sciences, Showa University, Japan) for his excellent support for statistical analysis.

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