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 Table of Contents  
Year : 2019  |  Volume : 6  |  Issue : 1  |  Page : 27-35

Uterine artery Doppler indices in pregnancy-induced hypertension in North Western Nigeria

1 Department of Radiology, Bayero University/Aminu Kano Teaching Hospital, Kano, Nigeria
2 Department of Radiology, Federal Medical Center, Bida, Niger, Nigeria

Date of Web Publication10-Oct-2019

Correspondence Address:
Dr. Mohammed K Saleh
Department of Radiology, Bayero University/Aminu Kano Teaching Hospital, Kano
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ssajm.ssajm_21_18

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Background: Pregnancy-induced hypertension (PIH) is a syndrome of hypertension with or without proteinuria, occurring when systolic blood pressure is greater than or equal to 140 mmHg and diastolic blood pressure is greater than or equal to 90 mmHg at gestational age of 20 weeks and above in a woman who has been previously normotensive. Doppler ultrasound (DUS) is now routinely used for evaluation of accessible vessels, hence its clinical application in patients with PIH. Aims and Objective: To evaluate the usefulness of DUS of the uterine artery (UA) in women with PIH. Materials and Methods: This was a prospective case–control study in which ultrasound examination of the uterus of 400 patients (200 hypertensive and 200 normotensive pregnant women) was performed. The UA Doppler indices, resistivity index, and systolic/diastolic ratio (RI and SD/DV) were recorded. Results: The mean RI in the PIH group (0.64 ± 0.07) was significantly higher than the mean of 0.50 ± 0.06 among the control group (t = 19.922, df = 398; P < 0.0001). In addition, the mean SD/DV ratio was significantly higher in the PIH group (3.04 ± 0.67) than in the control group (2.09 ± 0.29) (t = 18.270, df = 398; P < 0.0001). The Doppler spectral waveform patterns of the UA in both the groups revealed the presence of diastolic notch in 81.5% of the patients with PIH but in none of the control patients (Fisher’s exact P < 0.0001). Conclusion: Doppler parameters of the UA are abnormal in PIH, and its predictive value in PIH would be useful in the management of such patients.

Keywords: Doppler, hypertension, pregnancy, uterine artery

How to cite this article:
Saleh MK, Chawo J, Kazaure IS, Tabari AM, Kabiru I. Uterine artery Doppler indices in pregnancy-induced hypertension in North Western Nigeria. Sub-Saharan Afr J Med 2019;6:27-35

How to cite this URL:
Saleh MK, Chawo J, Kazaure IS, Tabari AM, Kabiru I. Uterine artery Doppler indices in pregnancy-induced hypertension in North Western Nigeria. Sub-Saharan Afr J Med [serial online] 2019 [cited 2023 Mar 27];6:27-35. Available from: https://www.ssajm.org/text.asp?2019/6/1/27/268785

  Introduction Top

Hypertension in pregnancy remains a major cause of maternal morbidity and mortality.[1],[2],[3],[4] Pregnancy-induced hypertension (PIH) includes the spectrum of gestational hypertension, preeclampsia, and eclampsia, and is a syndrome of hypertension with or without proteinuria and edema, occurring when systolic blood pressure (SBP) is greater than 140 mmHg and diastolic blood pressure (DBP) is greater than 90 mmHg.[5]

Doppler ultrasound (DUS) is utilized in examining uterine artery (UA) for Doppler indices and abnormal spectral waveform in patients with PIH.[5] In normal pregnancy, the systolic/diastolic (S/D) ratio of the UA is less than or equal to 2.6. Values above 2.6 may result in attendant fetal and maternal morbidities and mortalities.[6]

Early detection of abnormal placental vasculature before maternal and fetal complications developed would allow preventive interventions and improved maternal and fetal surveillance.[7] DUS scan is cheap, available, noninvasive, and does not use ionizing radiation,[8] hence it is applied in the assessment of the blood flow within the uterine arteries.

This study was to establish the effect of PIH on the Doppler parameters of the UA in our environment by assessing the resistive index (RI), S/D ratio, and presence of early diastolic notch, which represents increased impedance to blood flow during early diastole.

  Materials and methods Top

This was a prospective case–control study conducted at the Department of Radiology, Aminu Kano Teaching Hospital, Kano, North Western Nigeria, between January 2014 and June 2015. Two hundred pregnant patients referred from obstetrics and gynecology, general outpatient unit, and other referral centers, and with a history of newly diagnosed PIH were recruited. Equal number of pregnant women with normal blood pressure was also recruited from routine antenatal clinic to constitute the control group.

The sample size for the study was determined using the Fisher’s statistical formula with a prevalence of PIH of 31.3% as follows[9]:

This gave a minimum sample size of 330, which was approximated to 400 to allow for at least 10% due to attrition.

Hence, the total sample size was made up of 200 hypertensive pregnant women and 200 normotensive pregnant women (control study group).

The study group consisted of pregnant women with blood pressure of or greater than 140/90 mmHg or when the SBP was 30 mmHg or DBP was 15 mmHg above the recorded baseline blood pressure measured on two occasions 6 h apart, whereas the control group comprised pregnant women with no previous or current history of hypertension with blood pressure of less than 140/90 mmHg.

Pregnant women with the following conditions were excluded from the study:
  1. Diabetes mellitus confirmed by fasting blood glucose concentration value greater than 7 mmol/L.
  2. Chronic renal disease confirmed by standard laboratory values of electrolyte, urea, and creatinine.
  3. Fetal malformation seen on ultrasound scan.
  4. Multiple gestations seen on ultrasound scan.

A Mindray DC6 (Mindray DC6, Shenzen Mindray Bio-medical electronics company limited, China) expert equipped with Doppler facility and a 3.5-MHz convex probe with 100-Hz filter were used following liberal application of coupling gel to the abdomen.

Using color Doppler mode, the UA was identified in a view showing the bifurcation of the common iliac artery. Both UAs were studied. The recorded UA waveform was at the level where the UA crosses the external iliac artery [Figure 1] and [Figure 2]. The sampling range gate was placed over the entire diameter of the UA approximately 1 cm distal to the crossover point. This technique sampled low-velocity flow near the vessel wall. The quality of the flow velocity waveform (FVW) was maximized by using the smallest possible angle of insonation (range 15°–50°). The peak systolic velocity (PSV) and the end-diastolic velocity (EDV) were automatically displayed and the RI and S/D were generated by the ultrasound machine following activation of the calliper button on the keyboard.
Figure 1 Color Doppler sonogram, showing the uterine artery and the external iliac artery

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Figure 2 Doppler sonogram of the uterine artery showing early diastolic notch (arrow) in second trimester

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The RI of the UA for each patient was considered abnormal if greater than 0.58. If RI was abnormal at initial scan (20–24 weeks), the patient was rescanned 2 weeks later (at 22–26 weeks’ gestation) to validate the initial scan findings. Values were considered as abnormal if RI was >0.58 on both the occasions.

Before the commencement of the research, ethical approval was sorted and obtained from the Aminu Kano Teaching Hospital along with informed written consent from the patients involved in the study. Patients’ anonymity was ensured with all identification markers removed from the images. A female chaperone was always present during the course of the scan.

Patient data sheets were used to record the biodata and obstetric parameters of the hypertensive and normotensive pregnant women, along with the PSV, EDV, RI, and the S/D ratio. These were entered into the computer spreadsheet of the statistical package for social sciences for windows, version 21 (SPSS Inc., Chicago, Illinois, USA). The data were analyzed using analysis of variance (ANOVA), Chi-square, and correlation coefficient at 95% confidence interval. A P value of less than 0.05 was considered to be statistically significant. The findings are presented numerically, graphically, and in tabular forms.

  Results Top

Four hundred patients comprising 200 hypertensive (PIH) and 200 normotensive (controls) pregnant women were studied. [Table 1] shows the demographic characteristics of study patients. The mean age of patients with PIH was 28.2 ± 6.6 years. Although this was marginally higher than the value for the control participants (27.2 ± 4.9 years), this difference was not significant (P > 0.05). The age range was between 16 and 40 years in the PIH group and between 19 and 38 years in the control group. The largest number of patients with PIH (33.5%) was in the 31 to 35 year age group, whereas the modal group was 26 to 30 years among the control participants.
Table 1 Demographic characteristics of study patients

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The medical history and other clinical features are shown in [Table 2]. The mean gestational age in both the groups was 21.6 ± 1.6 weeks, and all the study participants in both the groups were in the second trimester of pregnancy [Figure 3]. The SBP was significantly higher among the PIH group (148.0 ± 19.1 mmHg) compared to 108.1 ± 10.7 mmHg among the control participants (t = 25.799, df = 398; P < 0.0001). Similarly, the DBP was significantly higher among the PIH patients (97.1 ± 12.8 mmHg) compared to controls (78.0 ± 6.9 mmHg) (P < 0.0001). A majority of the women were primigravidae in PIH (60.5%) and control group (61%). In the PIH group, previous history of PIH was present in 89 (44.5%), and preeclampsia/eclampsia was present in 54 (27.0%). Intrauterine fetal death (IUFD) was the fetal outcome in 11.1% of the PIH compared to 2.5% of the control group (χ2 = 11.572, df = 1; P < 0.0001) [Table 2].
Table 2 Clinical features among study patients

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Figure 3 Histograms showing the gestational age (EGA in weeks) distribution among the PIH and control groups

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A comparison of the mean RI and SD ratio among the study groups using the independent samples t-test is presented in [Table 3]. The mean RI in the PIH group (0.64 ± 0.07) was significantly higher than the mean of 0.50 ± 0.06 among the control group (t = 19.922, df = 398; P < 0.0001). In addition, the mean SD was significantly higher in the PIH group (3.04 ± 0.67) than in the control group (2.09 ± 0.29) (t = 18.270, df = 398; P < 0.0001). Chi-square analysis also showed that with a cutoff of 0.58 for the RI, a significantly higher proportion (82%) of the PIH patients were found to have abnormally high RI compared to the proportion of control (2%) participants (P < 0.0001).
Table 3 Doppler indices and USS findings among study patients

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In addition, a comparison of the Doppler spectral waveform patterns of the UA in both the groups revealed the presence of diastolic notch in 81.5% of the PIH patients and none among the control participants (Fisher’s exact P < 0.0001) [Table 3].

[Table 4] shows the results of a bivariate correlational analysis between the Doppler indices (RI and SD) and maternal age, estimated gestational age (EGA), SBP, and DBP. Among the patients with PIH, a positive and statistically significant but weak correlation was found between RI and maternal age (r = 0.375, P < 0.0001) [Figure 4], RI and EGA (r = 167, P < 0.05), RI and SBP (r = 0.243, P < 0.05), and RI and DBP (r = 0.225, P < 0.05). Although all these parameters negatively correlated with RI among the control group, only that with EGA was statistically significant (r = −0.246, P < 0.0001), which implies that with increasing gestational age (GA), there is a decrease in the RI. The scatter plot highlighting the relationship between RI and EGA in both the study groups is shown in [Figure 5]. In contrast, SD ratio correlated positively and significantly only with age (r = 0.230, P < 0.05) and DBP (r = 0.178, P < 0.05) among the patients with PIH. This implies that there is increase in the SD ratio with increase in maternal age and DBP. For the control group, a negative but generally weak correlation was found between SD and these characteristics. However, this was significant with only maternal age (r = −0.149, P < 0.05), EGA (r = −0.281, P < 0.0001), and DBP (r = −0.211, P < 0.005) [Table 4].
Table 4 Correlation between Doppler indices and patients’ characteristics

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Figure 4 Relationship between RI and maternal age among study population

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Figure 5 Relationship between RI and EGA in both the PIH and control population

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Further detailed analyses of the variation of both RI and SD with age among the two study groups are presented in [Table 5]. As highlighted by the results of a one-way ANOVA test in the table, RI increased from 0.59 ± 0.02 among patients with PIH aged 15 to 20 years, to the peak of 0.69 ± 0.04 among those aged 36 to 40 years (F = 9.486, df = 4, 185; P < 0.0001).
Table 5 One-way ANOVA for differences in mean Doppler indices by age

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In addition, among the patients with PIH, both RI and SD were higher in those with a history of previous PIH compared to those without it. However, as shown by a comparison of the mean RI and SD by independent samples t-test in [Table 6], only the difference with respect to RI was significant (0.66 ± 0.07 vs. 0.62 ± 0.07, t = 4.054, df = 188; P < 0.0001). Also in the same table, patients with PIH and a diastolic notch had significantly higher RI (0.65 ± 0.06) compared to those in whom it was absent (0.55 ± 0.06) (P < 0.001). The SD ratio was also significantly higher among patients with a diastolic notch (3.14 ± 0.65 vs. 2.38 ± 0.32, t = 6.043, df = 188; P < 0.0001).
Table 6 Differences in mean Doppler indices by previous history of PIH and Diastolic notch among PIH patients

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Furthermore, as shown in [Table 7], using the cutoff of 0.58 for normal (≤0.58) or abnormal (>0.58) RI, patients with PIH and a diastolic notch were significantly more likely to have an abnormally high RI compared to those without a diastolic notch (98.1% vs. 1.9%; Fisher’s exact P < 0.0001).
Table 7 Diastolic notch by RI in PIH patients

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  Discussion Top

In this study, the median maternal age was 29 years with similar age range of 16 to 40 years for PIH and 28 years with age range 19 to 38 years for normotensives [Table 1]. This is similar to the study by Groom et al.[10] in Franzcog (United States) wherein the median maternal age was 28 years. The influence of maternal age on the UA Doppler indices has shown weak correlation with RI. This study was comparable to the study of Oloyede and Iketubosin[11] in Lagos wherein maternal age correlated weakly with RI.

In this study, the proportion of primigravidae patients was higher (60.5%) in patients with PIH, which was comparable to the study by Oloyede and Iketubosin[11] (60.5%) in Lagos.

Arduini et al.[12] studied pregnancy of modal gestational age of 27 weeks compared to 20 to 24 weeks in this study. They found that the Doppler indices (RI and S/D) decrease with increasing gestational age. Findings by Groom et al.[10] on the pattern of change in UA Doppler between 20 and 24 weeks’ GA was consistent with this study. They recorded abnormal RI (>0.58) in the 3.7% of preeclamptic patients. This may be attributed to the early impairment of utero-placental perfusion, which may lead to subsequent villous vascular damage.

In this study, patients with PIH who developed preeclampsia/eclampsia had worse prognosis, particularly those with previous history of IUFD compared to the normotensives [Table 2]. This is in contrast to the study by Filippi et al.[13] in Netherland, where greater than one-fourth of hypertensive patients had intrauterine growth retardation (IUGR), which is also in agreement with the findings of Oloyede and Iketubosin[11] in Lagos where IUGR was one of the two most common complications among patients with PIH. It is speculated that reduced utero-placental perfusion due to impaired placentation may occur before 20 weeks and leads to IUGR.

The UA mean PSV in PIH was 63.10 cm/s; RI of 0.64, and S/D of 3.04 [Table 3] obtained from this study were similar to the values in the previous studies.[11] This study also shows that there was statistically significant difference between the values in PIH and normotensives. An apparent implication of this is that the DUS scan of the UA has a role in the screening for PIH. Different values for Doppler indices in PIH have been reported in various centers. In this study, findings are consistent with the study by Lakhkar et al.[14] who reported mean PSV range of 44 to 78 cm/s and mean RI of 0.59. The study by Lakhkar et al.[14] also shows RI findings dropping from 0.84 to 0.56 in the second trimester to 0.33 in the late third trimester with a mean S/D of 3.0. These findings were lower than the findings of Yakasai et al.[15] in Kano who reported mean PSV of 141.34 cm/s, mean RI of 0.7, and S/D above 3. The difference in the higher values in the Doppler indices may be attributed to the lower sample size in their study. The findings in this study are consistent with that of Oloyede and Iketubosin[11] in Lagos who recorded mean RI of 0.59 and 0.65 and S/D of 2.56 and 2.57. This is contrary to the study performed by Murakoshi et al.[16] in Niigata, Japan, where a lower mean RI and S/D ratio were recorded in patients with PIH. This may be due to the fact that in their study, Doppler waveforms were recorded from the spiral artery. In this study, the main UA Doppler waveform was recorded as it is suggested that the impedance to flow in the UA depends on the downstream impedance to flow in the spiral artery.

The presence of diastolic notch can also be used to define abnormal Doppler velocimetry. Diastolic notch was present in 81.5% of the patients with PIH in this study, and the patients with PIH and a diastolic notch were significantly more likely to have abnormally high RI compared to those without diastolic notch (98.1% vs. 1.9%). This agrees with the findings of Park et al.[17] in Korea, who observed high sensitivity of the diastolic notch in 20 to 24 weeks’ GA in the UA velocimetry for prediction of PIH (73%). These findings were consistent with the reports of Aristidou et al.[18] and Bower et al.[19] that the presence of a diastolic notch of the UA FVW is a better predictor of preeclampsia than the UA RI. These observations strongly suggest that a diastolic notch of the UA FVW in the second trimester reflects high vascular resistance in the utero-placental bed caused by incomplete trophoblastic invasion of the spiral arteries.

This study has opened up a new functional dimension in diagnostic ultrasound. With the use of Doppler technology, it has been possible to show a strong positive correlation between uterine vascular resistance, expressed by an elevated RI and/or persistence of an early diastolic notch in the Doppler waveform and PIH.[20] Several studies have shown a reduction in the maternal uterine RI with advancing gestational age in normal pregnancy,[21] whereas the presence of an increased resistance in maternal flow or the presence of a notch, as evidence of abnormal UA flow,[22] has been associated with the development of PIH. Many Doppler studies of uterine circulation revealed the potential of this technique to predict and manage high-risk pregnancies. For many years, the DUS evaluation of uterine arteries was used to predict pregnancy outcome.[22]

In addition, before this new technology is accepted as a standard pregnancy surveillance tool, the baseline data of Doppler indices that is devoid of influence of racial factors must be collected and the normative data derived from the local population.

High-risk group should be identified which should be further investigated by Doppler ultrasonography.[23] The aim of this prediction is to help stratify the antenatal women so as to intensify subsequent surveillance.[23] Although there is the potential anxiety associated with being classified as being at high risk for PIH, such a classification does not carry a direct risk to the mother or the fetus.[23]

The reference values for Doppler indices of the UA were established in normotensive pregnant women and significantly higher values were seen in patients with PIH. The presence of high RI and S/D of the UA or the appearance of diastolic notch is associated with an increased risk of development of PIH. However, combination of parameters is superior to the use of a single parameter, because it was found that abnormal RI, S/D, and early diastolic notch were found to be higher in patients with PIH than the normotensives.

Doppler indices of the UA can be used as antenatal surveillance tool for the prediction of PIH.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Antsaklis A, Daskalakis G, Tzortis E, Michalas S. The effect of gestational age and placental location on the prediction of preeclampsia by uterine artery Doppler velocimetry in low risk nulliparous women. Ultrasound Obstet Gynecol 2000;16:635-39.  Back to cited text no. 1
Itam HI, Ekabule JE. A review of pregnancy outcome in women with eclampsia at the university of Calabar Teaching Hospital, Calabar. Trop J Obstet Gynaecol 2002;18:66-8.  Back to cited text no. 2
Vanderjagt DJ, Patel RJ, El-Nafaty AU, Melah GS, Crossey MJ, Glew RH. High-density lipoprotein and homocysteine levels correlate inversely in preeclamptic women in northern Nigeria. Acta Obstet Gynaecol Scand 2004;83:536-42.  Back to cited text no. 3
Stampalija T, Gyte GML, Alfirevic Z. Utero-placental Doppler ultrasound for improving pregnancy outcome. Cochrane Database Syst Rev 2010;9:CD008363.  Back to cited text no. 4
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Fleischer A, Schulman H, Farmakides G, Bracero L, Grunfeld L, Rochelson B et al. Uterine artery Doppler velocimetry in pregnant women with hypertension. Am J Obstet Gynecol 1986;154:806-13.  Back to cited text no. 6
Abubakar A, Abdullahi RA, Jibril HZ, Dauda MH, Poopola MA. Maternal ethnicity and severity of pre-eclampsia in Northern Nigeria. Asian J Med Sci 2009;1:104-7.  Back to cited text no. 7
Barnett SB, Maulik D. Guidelines and recommendations for safe use of Doppler ultrasound in perinatal applications. J Matern Fetal Neonatal Med 2001;10:75-84.  Back to cited text no. 8
Ekele BA, Bello SO, Adamu AN. Clusters of eclampsia in a Nigerian teaching hospital. Int J Gynaecol Obstet 2007;96:62-6.  Back to cited text no. 9
Groom KM, North RA, Stone PR, Chan EH, Taylor RS, Dekker GA. Patterns of change in uterine artery Doppler studies between 20 and 24 weeks of Gestation and pregnancy outcome. Obstet Gynaecol 2009;113:332-8.  Back to cited text no. 10
Oloyede O.A., Iketubosin F. Uterine artery Doppler study in second trimester of pregnancy. Pan Afr Med J 2013;15:87.  Back to cited text no. 11
Arduini D, Rizzo G, Romanini C, Mancuso S. Utero-placental blood flow velocity waveforms as predictors of pregnancy induced hypertension. Eur J Obstet Gynecol 1987;26:335-41.  Back to cited text no. 12
Filippi E, Staughton J, Peregrine E, Jones P, Huttly W, Peebles M et al. Uterine artery Doppler and adverse pregnancy outcome in women with extreme levels of fetoplacental proteins used for Down syndrome screening. Ultrasound Obstet Gynecol 2011;37:s20-7.  Back to cited text no. 13
Lakhkar BN, Ahmad SA. Doppler velocimetry of uterine and umbilical arteries during pregnancy. Genitourin Radiol 1999;119-25.  Back to cited text no. 14
Yakasai IA, Tabari AM, Rabiu A, Ismail A. Pattern of fetal arterial blood flow in selected vessels in patients with pregnancy induced hypertension in Aminu Kano Teaching Hospital Kano, Nigeria. West Afr J Radiol 2013;20:9-13.  Back to cited text no. 15
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Aristidou A, Van den Hof MC, Campbell S, Nicolaides K. Uterine artery Doppler in the investigation of pregnancies with raised maternal serum alpha-fetoprotein. Br J Obstet Gynecol 1997;10;431-5.  Back to cited text no. 18
Bower S, Bewley S, Campbell S. Improved prediction of preeclampsia by two-stage screening of uterine arteries using the early diastolic notch and color Doppler imaging. Obstet Gynecol 1993;82:78-83.  Back to cited text no. 19
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Bower S, Schuchter K, Campbell S. Doppler ultrasound screening as part of routine antenatal scanning: Prediction of pre-eclampsia and intrauterine growth retardation. Br J Obstet Gynaecol 1993;100:989-94.  Back to cited text no. 22
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]


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