DOI: 10.1055/s-0036-1594288 - volume 38 - Dezembro 2016
Mariarosaria Di Tommaso, Giulia Martello, Tomi Kanninen, Federica Perelli, Laura Iannuzzi, Giovanni Sisti
Fetal heart rate (FHR) monitoring has provided the most reliable indicator of fetal wellbeing in clinical practice; however, its control mechanisms are still poorly understood. Cardiotocog-raphy (CTG) monitoring of FHR is a noninvasive method that has been augmented recently by advances in computerized CTG (cCTG) analysis, with the latest generation technology super-seding past inefficiencies to demonstrate superior results re-garding visual analysis.1 However, CTG has faced criticism2 (due to its high false positive rate), and researchers have suggested that more randomized studies are necessary.3 Past studies have also suggested a variability in CTG results with ethnicity.4-6
The ethnic origin has been demonstrated as being an inde-pendent factor for the development of many clinical conditions, such as hypertension, diabetes, atherosclerosis and coronary heart disease, in newborns,7 children,8 adolescents9 and adults.10 Ethnic disparities have also been suggested as a co-factor in many pregnancy complications.11 Based on recent projections of the US Census Bureau, the US adult population will gradually become more diverse in the near future, with several different racial or ethnic groups.12
Studies dated to more than 10 years ago have demonstrat-ed worse CTG tracings in the fetuses of black women when compared with those of white women.4-6
Only a few studies have investigated whether race itself could lead to a bad non-stress test (NST) when excluding all others cofactors. Whether race acted as a surrogate marker for socioeconomic status in these studies remains unclear. The potential biases of these studies are the lack of paternal ethnic origin information, the lack of information on CTG indication,6 and the fact that NST reactivity can only be determined visually.4,6 The former bias is significant, given the substantial progress cCTG analysis has had over the past 20 years.3
The aim of this study was to verify if the maternal and paternal ethnic origins could influence the fetal cCTG in singleton pregnancies, excluding other cofactors.
This is a retrospective cross-sectional study comparing the results of the cCTG of pregnant patients at 37-42 weeks in two maternal-fetal medicine centers in northern Italy (Udine and Pordenone) according to parental ethnicity. The study was approved by the local Ethics Committee, and all the patients provided written consent. The NST was performed on a routine basis after the 37th gestational week, according to the national guidelines. Ethnicity was catego-rized as black (group B, including all African States, n 1/4 19) and white (group W, including all European States, n 1/4 34). Only pregnant patients with the same ethnicity as their fathers were included in the study. The other inclusion criteria were: singleton pregnancy after week 37 with ab-sence of any maternal and fetal morbidity, such as gestational or pre-gestational diabetes mellitus; hypertensive disorders of the pregnancy, including preeclampsia, intra-uterine growth retardation (IUGR); and fetal malformation. A cCTG (8002 Sonicaid Fetal Care System, Oxford Sonicaid, UK) was performed to analyze the variables of FHR. The cCTG variables analyzed were: percentage of signal loss; number of contractions; basal FHR; number of accelerations (10-15 bpm and > 15 bpm); number of decelerations; length of high variation episodes; short-term variability (STV); total trace duration time; and number of fetal active movements. The cCTGs were performed by the midwife/ nurse on call, under the supervision of an ob-gyn physician (there were two of them in each of the maternal-fetal medicine centers) with excellent obstetric background training.
Patient data not normally distributed were described as median (25°-75° percentile), whereas variables normally distributed were described as mean (standard error). The Mann-Whitney non parametric test for continuous data and the Chi-square test were used to compare the two groups. A p-value < 0.05 was considered statistically significant. The Sta-tistical Package for Social Sciences (SPSS) software v. 22.0 (IBM, Chicago, Illinois, US) was used for the statistical analysis.
Nineteenpatients were included ingroup B, and 34 ingroupW. Groups B and W were matched for maternal age, gestational age, body mass index (BMI), fetal sex and smoking (►Table 1). Parity was higher in black women (►Table 1), but this factor is not believed to influence computerized non-stress test (cNST) results. The most representative State of origin in group B was Morocco (37%), and Italy (76%) for group W (data not shown). The trace length was not statistically differently distributed between the two groups (►Table 1).
Table 1
Demographic and baseline characteristics of the population
| Black (n = 19) | White (n = 34) | p-value | |
|---|---|---|---|
| Maternal age (years) | 31.2 | 29.7 | 0.861 |
| Gestational age (weeks) | 38 [38–40] | 39 [38–40] | 0.759 (Mann-Whitney) |
| BMI (kg/m2) | 26 [22.8–27.5] | 23 [20.1–27.5] | 0.073 (Mann-Whitney) |
| Parity | 4 = 015 ≥ 1 | 18 = 016 ≥ 1 | 0.024 (Chi-square) |
| Fetal Sex | 9 female, 10 male | 17 female, 17 male | 0.854 (Chi-square) |
| Smoker | 0/19 | 4/34 | 0.120 (Chi-square) |
| Total trace time length (min) | 31.0 [24–43] | 28.0 [14.7–35.7] | 0.137 |
Abbreviation: BMI, body mass index.
The perinatal outcomes did not significantly differ be-tween the two groups: the gestational age at delivery was 39.6 years (38.8-40.5 years) in group B, against 39.8 years (38.8-40.6 years) in group W; newborn weight was 3.435 kg (3.155-3.710) in group B, against 3.460 kg (3.190-3.750) in group W; the Apgar score at 1 minute was 8.3 (0.1) in group B, against 8.5 (0.2) in group W; and the Apgar score at 5 minute was 9.5 (0.1) in group B, against 9.6 (0.1) in group W.
The cNST results when comparing the two groups were the same regarding: percentage of signal loss; number of contractions; basal FHR; number of accelerations (10-15 bpm and > 15 bpm); number of decelerations; length of high variation episodes; STV; and total trace duration time (►Table 2). The long-term variability was always > 5 bpm, and as such, it was not included in the analysis. Statistically significant differences were recorded in number of fetal active movements (20 [8-35] in group B, against 39 [19.2- 73.5] in group W) and minutes of low variation (0 [0-11] in group B, against 0 in group W [0-0]) (►Table 2).
In this study we found a significantly lower number of active fetal movements and longer periods of low variation in the cCTG of black patients when compared with white patients.
Paine et al5 were the first to hypothesize that race was a significant co-factor influencing NST results. They conducted the first small prospective study on 100 patients,5 and a larger retrospective study later.6 In their study, the visual interpretation of the NST was used classifying the trace as reactive or non-reactive. In 1998, Ogueh et al4 conducted a small prospective study with 96 patients. They found signifi-cant differences when comparing cCTG in the population groups according to maternal ethnicity. However, the pater-nal ethnicity was not considered.
Racial differences in the adult population are a well-known risk factor for cardiovascular risk and for heart rate variabili-ty.13 Recent evidence has suggested that these differences are present only because of the influence of the individual genetic variance, regardless of other cardiovascular factors.14 We speculate that the same genetic racial disparity exists in fetal life, and can be detected by modern ultra-sensitive cCTG.
Table 2
Differences in CTG results according to parental ethnicity
| Black (n = 19) | White (n = 34) | p (Mann-Whitney) | |
|---|---|---|---|
| Signal loss (%) | 1.6 [0.4–3.1] | [0.075–2.75] | 0.132 |
| Number of contractions | 1 [0.0–3.0] | 1 [0–2] | 0.886 |
| Fetal active movements (n/h) | 20 [8–35] | 39 [19.2–73.5] | 0.007 |
| Basal FHR(bpm) | 137 [130–145] | 134.5 [128–139.5] | 0.150 |
| Number of accelerations (10–15 bpm) | 3 [1–8] | 3.5 [1–9] | 0.730 |
| Number of accelerations (> 15 bpm) | 3 [1–10] | 3.5 [2–6] | 0.181 |
| Number of decelerations | 1 deceleration | 0 decelerations | N/A |
| Length of high variation episodes (min) | 14 [1–20] | 15.0 [10–20.5] | 0.788 |
| Length of low variation episodes (min) | 0.0 [0–11] | 0.0 [0–0] | 0.047 |
| STV (msec) | 9.4 [8.1–13.1] | 10.8 [9.1–11.6] | 0.258 |
Abbreviations: CTG, Cardiotocography; FHR, fetal heart rate; STV, short-term variability.
Moreover, this is the first time that the newer genera-tion of cCTG has been adopted to report ethnic differences in a pregnant population. Over the past 20 years, there has been tremendous improvement in this technology, leading to a significant reduction in perinatal mortality.3 cCTG can reveal to the physician the fetal heart STV, which cannot be obtained by visual assessment alone. Short-term variabili-ty has been shown to be closely related with the fetal wellbeing, and significantly reduced STV is a sign of fetal academia.15-17 cCTG significantly lowered perinatal mor-tality compared with traditional CTG in a selected popula-tion,3 but to date there are not enough studies supporting the routine use of CTG in all pregnancies, as outlined by a recent meta-analysis.
To our knowledge, this is the first time that both maternal and paternal ethnicities have been considered, and this is one of the strengths of our study. Fetal DNA is equally derived from the contributions of both mother and father. Recently, a study outlined the importance of both parents' ethnicity on the risk of stillbirth in the offspring.18 Surprisingly, no prior studies have considered this factor when analyzing the genetic influence on NST readings.4-6
We do acknowledge the limitations of our study, primarily the retrospective nature and the low number of patients in each group.
Though the clinical use of the CTG has undoubtedly benefit-ed patients, there remains criticism against its use and reliabili-ty, mainly in regard to its false positive rate. Identifying the factors responsible for variance in the objective analysis of CTG results is important to improve the outcomes of patients. Our study lends further evidence as to the importance of ethnicity in clinical cCTG interpretation. Further studies are needed to confirm our finding in a larger population.