Keywords
fetal growth restriction - doppler - cerebroplacental ratio - agreement - correlation
Palavras-chave
restrição do crescimento fetal - doppler - relação cérebro-placentária - concordância
- correlação
Introduction
Fetal growth restriction (FGR) occurs when the conceptual product does not reach its
intrauterine growth and development potential. However, in the clinical practice,
FGR is difficult to define, and, to date, there is no gold standard method for its
diagnosis.[1] Fetal growth restriction can be secondary to numerous conditions that include congenital
malformations, chromosomal disorders, and intrauterine infections; however, most cases
of FGR occur as a consequence of placental insufficiency that can lead to fetal hypoxia.[2]
One of the first investigations regarding the clinical importance of FGR was performed
by Lubchenco et al.,[3] who determined the fetal weight in relation to gestational age at the time of delivery.
This analysis resulted in an increase in perinatal morbidity and mortality in newborns
weighing < 10th percentile for gestational age. However, the definition of FGR using only the estimated
fetal weight (EFW) < 10th percentile would also encompass fetuses small for gestational age (SGA), and a distinction
between restricted (those at high risk of perinatal complications) and SGA fetuses
is necessary.[4]
The society of Maternal-Fetal Medicine states that the prenatal detection of FGR can
improve the perinatal outcome through appropriate fetal monitoring and optimization
of the time of delivery.[5] Doppler has become an essential tool in the diagnosis and management of FGR. Some
Doppler indices can be used to evaluate the waveform of both maternal and fetal vessels:
resistance index (RI), represented by the systole-diastole/integral mean velocity
of the spectral area, and the pulsatility index (PI), represented by the systole-diastole/systole.
When RI is used, the Doppler waveform is represented only on a scale of 0 to 1 and
has been reported to have a linear relationship with gestational age. In comparison,
it is believed that the use of the PI allows continuous waveform analysis over a more
extensive range of waveform patterns in addition to having a quadratic relationship
with gestational age.[6]
The Doppler assessment in FGR is based on the assessment of fetal well-being by examining
the compensatory signs triggered by hypoxemia in the fetal circulation.[7] In the PORTO study, regardless of EFW or abdominal circumference (AC), the strongest
and most significant association with adverse perinatal outcomes in the low-risk population
was found when umbilical artery (UA) Doppler was altered. The authors suggest that
EFW < 3rd percentile or the combination of EFW < 10th percentile with abnormal UA Doppler represent an increased risk of any adverse perinatal
outcome or admission to the neonatal intensive care unit (ICU) compared with EFW or
AC < 10th percentile but with normal UA Doppler.[8]
In the last decade, other factors that could help differentiate between SGA and FGR
have been investigated; when altered, these parameters were associated with adverse
perinatal outcomes. Estimated fetal weight or AC < 3rd percentile, uterine artery (UtA) Doppler > 95th percentile, middle cerebral artery (MCA) Doppler < 5th percentile, and alteration in cerebroplacental ratio (CPR) were associated with adverse
perinatal outcomes in low-weight fetuses. In the current FGR concept, UA Doppler should
no longer be used as a single standard to determine diagnosis and prognosis. According
to the criteria of Figueiras and Gratacós[9] FGR can be defined through the EFW < 3rd percentile or the EFW between the 3rd and 10th percentile associated with altered maternal-fetal Doppler parameters.
Currently, the FGR is divided into early- and late-onset, with a cutoff of 32 weeks
of pregnancy. However, this division does not represent only the gestational age at
the diagnosis, but two entities with different natural histories and distinct biochemical,
histological, and clinical characteristics.[7]
In this context, we decided to investigate the behavior of maternal-fetal Doppler
parameters and the CRP in fetuses with FGR and to evaluate the degree of agreement/correlation
of maternal-fetal Doppler parameters between normal and FGR fetuses.
Methods
The present observational and retrospective study was conducted in a private clinic
of fetal medicine and at the Department of Gynecology and Obstetrics of the Universidade
Federal do Paraná (UFPR, in the Portuguese acronym), Curitiba, state of Paraná, Brazil,
between July 2017 and May 2019. The present study was approved by the Ethics Committee
of UFPR, and consent form was not necessary as it was a retrospective study.
In total, 502 obstetrical ultrasound examinations with maternal-fetal Doppler parameters
of 274 pregnant women were analyzed in the present study. The criteria of Figueiras
and Gratacós were considered to evaluate the occurrence of FGR.[9] The sample inclusion criteria were singleton pregnancies from 24 weeks, considered
to be at low risk or with FGR. The gestational age was determined by the last menstrual
period and confirmed by ultrasound examination performed until 13 + 6 weeks of gestation
using the crown-rump length.
The ultrasound examinations were performed by 10 doctors specialized in fetal medicine,
who used the Voluson 730 PRO (General Electric Healthcare Zipf, Austria) and Accuvix
V10 (Samsung-Medison, Seoul, South Korea) apparatus.
Data were collected regarding the gestational age at ultrasound examination, EFW with
its percentile in the respective ultrasound examination, fetal abnormalities observed
on the obstetric ultrasound examinations, and findings from the Doppler examination.
Calculations were made to assess the respective percentiles of the RI and PI observed
in the UtA, UA, MCA, and CPR with the Fetal ID calculator, v.2017 found on the Fetal
Medicine Web site of Barcelona (https://medicinafetalbarcelona.org/calc). The CPR was obtained by dividing the PI of the MCA by the PI of the UA. Additionally,
the umbilical-cerebral ratio (U/C) was obtained by dividing the RI of the UA by the
RI of the MCA.
To assess the occurrence of FGR, the following criteria, according to Figueiras and
Gratacós,[9] were considered: EFW < 3rd or between the 3rd and 9th percentiles according to the table by Hadlock et al.[10] Additionally, the criteria also included at least 1 of the following conditions:
UAt Doppler > 95th, UA Doppler > 95th, MCA Doppler < 5th, and CPR < 5th percentile. The U/C was considered altered if it was > 1.0.[11]
The sample size was calculated to estimate the percentage of FGR. Considering an estimate
of 6.8% for this percentage (Figueras et al.),[12] a sample of 271 fetuses would be sufficient to estimate this parameter with a margin
of error of 3% and 95% confidence interval (CI).
The results of quantitative variables were described by means, standard deviations
(SDs), medians, and ranges. Categorical variables were described by frequencies and
percentages. A 95% CI was presented for determining the percentage of FGR. Spearman
correlation coefficients were estimated to assess the correlation between PI and RI
of maternal-fetal Doppler parameters. The agreement between two Doppler parameters
was assessed by estimating the Kappa coefficient. The values of p < 0.05 indicated statistical significance. The data were analyzed using IBM SPSS
Statistics for Windows, version 20.0 (IBM Corp., Armonk, NY, USA).
Results
The present analysis was based on the data from 274 pregnant women who underwent Doppler
examinations between 1 and 7 times from 24 weeks of gestation; moreover, 136 (49.6%)
pregnant women underwent Doppler examination only 1 time. In total, 502 Doppler examinations
were included in the study, and FGR was observed in 19 of 274 fetuses, with 4 early-onset
(< 32 weeks) and 15 late-onset cases of FGR (≥ 32 weeks). Hence, it was estimated
that the percentage of FGR was equal to 6.9% with a 95%CI (3.9–9.9%). Of the 274 pregnant
women, 11 (4%) had any EFW < 3rd percentile, 28 (10.2%) had any EFW assessment between the 3rd and 9th percentiles, and 235 (85.8%) had EFW ≥ 10th percentile. [Table 1] shows the descriptive analysis of all the maternal-fetal Doppler parameters.
Table 1
Descriptive analysis of maternal–fetal Doppler parameters
|
Doppler parameter
|
GA (weeks)
|
n
|
Mean
|
Median
|
Minimum
|
Maximum
|
Standard deviation
|
|
RI Right UAt
|
≤ 28
|
51
|
0.51
|
0.49
|
0.22
|
1.71
|
0.20
|
|
28.1–32
|
112
|
0.49
|
0.48
|
0.23
|
0.85
|
0.10
|
|
32.1–36
|
178
|
0.47
|
0.46
|
0.27
|
0.81
|
0.10
|
|
> 36
|
161
|
0.45
|
0.44
|
0.08
|
0.77
|
0.10
|
|
PI Right UAt
|
≤ 28
|
51
|
0.77
|
0.73
|
0.28
|
2.17
|
0.30
|
|
28.1–32
|
112
|
0.77
|
0.71
|
0.27
|
2.37
|
0.31
|
|
32.1–36
|
178
|
0.71
|
0.67
|
0.34
|
1.71
|
0.24
|
|
> 36
|
161
|
0.67
|
0.63
|
0.32
|
1.77
|
0.20
|
|
RI Left UAt
|
≤ 28
|
51
|
0.52
|
0.52
|
0.35
|
0.89
|
0.10
|
|
28.1–32
|
112
|
0.49
|
0.48
|
0.30
|
0.74
|
0.09
|
|
32.1–36
|
178
|
0.47
|
0.47
|
0.17
|
0.76
|
0.09
|
|
> 36
|
161
|
0,45
|
0.44
|
0.24
|
0.78
|
0.09
|
|
PI Left UAt
|
≤ 28
|
51
|
0.80
|
0.77
|
0.45
|
1.65
|
0.22
|
|
28.1–32
|
112
|
0.75
|
0.70
|
0.36
|
1.79
|
0.23
|
|
32.1–36
|
178
|
0.71
|
0.68
|
0.24
|
1.90
|
0.23
|
|
> 36
|
161
|
0.67
|
0.61
|
0.30
|
1.70
|
0.21
|
|
PI UA
|
≤ 28
|
51
|
1.14
|
1.14
|
0.57
|
1.89
|
0.20
|
|
28.1–32
|
112
|
1.01
|
1.02
|
0.61
|
1.67
|
0.19
|
|
32.1–36
|
178
|
0.90
|
0.89
|
0.55
|
1.48
|
0.17
|
|
> 36
|
161
|
0.85
|
0.84
|
0.45
|
1.22
|
0.15
|
|
Percentile UA
|
≤ 28
|
51
|
45.69
|
46.00
|
3.00
|
99.00
|
20.41
|
|
28.1–32
|
112
|
46.16
|
46.00
|
5.00
|
98.00
|
20.34
|
|
32.1–36
|
178
|
43.92
|
41.00
|
8.00
|
96.00
|
20.06
|
|
> 36
|
161
|
41.82
|
40.00
|
6.00
|
84.00
|
17.85
|
|
RI UA
|
≤28
|
51
|
0.70
|
0.70
|
0.45
|
0.88
|
0.07
|
|
28.1–32
|
112
|
0.64
|
0.65
|
0.45
|
0.83
|
0.07
|
|
32.1–36
|
178
|
0.59
|
0.60
|
0.43
|
0.79
|
0.07
|
|
> 36
|
161
|
0.57
|
0.57
|
0.38
|
0.73
|
0.06
|
|
PI MCA
|
≤28
|
51
|
2.21
|
2.22
|
1.43
|
3.09
|
0.45
|
|
28.1–32
|
112
|
2.17
|
2.13
|
0.86
|
3.65
|
0.51
|
|
32.1–36
|
178
|
1.93
|
1.88
|
0.73
|
4.30
|
0.47
|
|
>36
|
161
|
1,60
|
1.51
|
0.84
|
2.60
|
0.33
|
|
RI MCA
|
≤ 28
|
51
|
0.89
|
0.88
|
0.74
|
1.00
|
0.08
|
|
28.1–32
|
112
|
0.88
|
0.87
|
0.57
|
1.06
|
0.08
|
|
32.1–36
|
178
|
0.83
|
0.83
|
0.62
|
1.04
|
0.07
|
|
> 36
|
161
|
0.77
|
0.76
|
0.55
|
1.00
|
0.07
|
|
CPR
|
≤ 28
|
51
|
1.98
|
1.93
|
1.21
|
3.45
|
0.50
|
|
28.1–32
|
112
|
2.20
|
2.15
|
0.51
|
4.15
|
0.60
|
|
32.1–36
|
178
|
2.20
|
2.16
|
0.69
|
3.98
|
0.58
|
|
> 36
|
161
|
1.94
|
1.87
|
1.15
|
5.04
|
0.56
|
|
Percentile CPR
|
≤28
|
51
|
50.37
|
56.00
|
4.00
|
99.00
|
30.98
|
|
28.1–32
|
112
|
53.04
|
51.50
|
1.00
|
99.00
|
31.08
|
|
32.1–36
|
178
|
52.86
|
53.00
|
1.00
|
99.00
|
30.04
|
|
> 36
|
161
|
43.07
|
38.00
|
3.00
|
99.00
|
30.07
|
|
U/C
|
≤ 28
|
51
|
0.79
|
0.80
|
0.58
|
0.99
|
0.10
|
|
28.1–32
|
112
|
0.74
|
0.73
|
0.45
|
1.46
|
0.11
|
|
32.1–36
|
178
|
0.72
|
0.71
|
0.51
|
1.08
|
0.10
|
|
> 36
|
161
|
0.74
|
0.75
|
0.46
|
0.95
|
0.10
|
|
Percentile MCA
|
≤ 28
|
51
|
59.47
|
67.00
|
4.00
|
99.00
|
31.72
|
|
28.1–32
|
112
|
56.79
|
60.00
|
1.00
|
99.00
|
32.66
|
|
32.1–36
|
178
|
52.30
|
53.50
|
1.00
|
99.00
|
30.11
|
|
> 36
|
161
|
48.09
|
46.00
|
1.00
|
99.00
|
29.16
|
Abbreviation: CPR, cerebroplacental ratio; GA, gestational age; MCA, middle cerebral
artery; PI, pulsatility index; RI, resistance index; U/C, umbilical–cerebral ratio;
UA, umbilical artery; UAt, uterine artery.
[Table 2] shows the correlation between RI and PI of UtA, UA, and MCA of all Doppler examinations.
According to the Spearman correlation coefficient, there was an expressive and significant
correlation between the Doppler parameters (p < 0.001) ([Fig. 1]).
Fig. 1 Correlation between resistance (RI) and pulsatility (PI) indices of maternal–fetal
Doppler parameters.
Table 2
Correlation between maternal–fetal Doppler parameters
|
Variables
|
n
|
Spearman's correlation coefficient
|
p-value
|
|
RI Right UAt versus PI Right UAt
|
502
|
0.97
|
< 0.001
|
|
RI Left UAt versus PI Left UAt
|
502
|
0.97
|
< 0.001
|
|
RI UA versus PI UA
|
502
|
0.97
|
< 0.001
|
|
RI MCA versus PI MCA
|
502
|
0.96
|
< 0.001
|
Abbreviations: MCA, middle cerebral artery; PI, pulsatility index; RI, resistance
index; UA, umbilical artery; UAt, uterine artery.
The CPR percentile was normal in 476 of 502 (94.8%) and altered in 26 of 502 (5.2%)
examinations. In contrast, U/C was normal in 498 of 502 (99.2%) and altered in 4 (0.8%)
examinations. Of the 502 Doppler examinations, there was an agreement between U/C
and CPR percentiles in 480 (95.6%) and disagreement in 22 (4.4%) examinations ([Table 3]). In all the cases of disagreement, U/C was normal, and the CPR percentile was altered.
The estimated Kappa coefficient of agreement was 0.26 with 95%CI (0.05–0.46), thereby
corresponding to a weak agreement.
Table 3
Description of the percentile of cerebroplacental ratio by the percentile of umbilical–cerebral
ratio
|
Percentile CPR
|
U/C
|
Total
|
|
Normal (≤ 1)
|
Altered (> 1)
|
|
Normal (≥ 5th)
|
476
|
0
|
476
|
|
94.8%
|
0.0%
|
94.8%
|
|
Altered (< 5th)
|
22
|
4
|
26
|
|
4.4%
|
0.8%
|
5.2%
|
|
Total
|
498
|
4
|
502
|
Abbreviations: CPR, cerebroplacental ratio; U/C, umbilical–cerebral ratio.
Of the 68 cases with EFW ≤ 9th percentile (SGA), there was an agreement between U/C > 1.0 and CPR < 5th percentile for 61 (88.4%) and disagreement in 7 (5.8%) Doppler examinations. In all
cases of disagreement, the U/C > 1.0 was “no” and the CPR < 5th percentile was “yes” ([Table 4]). The estimated Kappa coefficient of agreement was 0.49 with 95%CI (0.13–0.85),
thereby corresponding to a moderate agreement.
Table 4
Analysis of agreement between CPR (< 5th) and U/C (> 1.0) in fetuses with estimated
weight ≤ 9th percentile
|
CPR (< 5th)
|
U/C (> 1.0)
|
Total
|
|
No
|
Yes
|
|
No
|
57
|
0
|
52
|
|
89.1%
|
0.0%
|
|
Yes
|
7
|
4
|
16
|
|
10.9%
|
100%
|
|
Total
|
64
|
4
|
68
|
Abbreviations: CPR, cerebroplacental ratio; U/C, umbilical–cerebral ratio.
Discussion
Although FGR is one of the greatest challenges in obstetrics, there is still no treatment
that can reverse placental insufficiency. In this context, the management of these
patients is of fundamental importance. Additionally, Doppler examination is crucial
in assessing the fetal well-being and deciding the moment of delivery while examining
the risks of prematurity with the risks of fetal death.
It is important to perform fetal Doppler examination with the correct technique. Similarly,
its interpretation is also important along with the knowledge of the most appropriate
Doppler parameter (PI or RI) to attest the fetal vitality. In our study, we obtained
an excellent correlation between the PI and RI of UA, MCA, and UtA; hence, both PI
and RI can be used in the follow-up of FGR. This result is consistent with studies
in the literature such as the one by Khanduri et al.,[13] who concluded that both the PI and the RI of the UA have a similar accuracy for
the diagnosis of FGR. Another study, conducted by Rani et al.,[14] showed that the PI and RI of both UA and MCA had a similar accuracy to predict adverse
perinatal outcomes in pre-eclampsia.
Also corroborating with our study, Cnossen et al.[15] conducted a systematic review with meta-analysis demonstrating that, in the 2nd trimester, both the PI and RI of the UtA present a similar performance for the prediction
of FGR (positive likelihood ratio for RI = 2.4 and for PI = 2.3) in the high-risk
pregnant women.
Cerebroplacental ratio is a new Doppler tool that has recently been gaining prominence
in the monitoring of FGR, so much so that it has been included in the recent classification
of expert consensus based on the Delphi method to assist in the diagnosis of late-onset
FGR.[14] Cerebroplacental ratio has been shown to be more sensitive to hypoxia than its individual
components and demonstrates a better correlation with adverse perinatal outcomes in
SGA or FGR. Triunfo et al.[16] showed that CPR improves the prediction of adverse perinatal outcomes compared with
only the EFW in low-risk pregnancies at 37 weeks. Morales-Roselló et al.[17] evaluated 891 fetuses between 34 and 41 weeks and concluded that CPR was the parameter
that best predicted adverse perinatal outcomes at the end of pregnancy.
There are some references for the use of this Doppler tool, and two of them were studied:
the CPR, which is the ratio of the PI of the MCA divided by the PI of the UA, and
the U/C, which is the ratio of the RI of the UA divided by the PI of the MCA. The
data from our study showed that, for FGR cases, there was only a moderate correlation
between the two parameters (kappa = 0.49) and that the use of PI would be more accurate.
However, in the literature, the multicentric study PORTO[6] and the study of To et al.[11] showed that it would be possible to use both the PI and RI. The PORTO study[6] compared the CPR performed with PI and RI values to predict the adverse perinatal
outcomes, and To et al.[11] compared the CPR to assess the need for an operative delivery. In both studies,
the authors obtained a good correlation between the use of PI and RI. A possible explanation
for this difference in our results in the relationship to previous studies may be
the smaller number of FGR cases in our sample. Additionally, another possible bias
was that a fixed value was used for the normality value for the U/C, whereas a reference
curve variable according to the gestational age was used for CPR.
Although Doppler examination plays a very important role in FGR and can identify placental
insufficiency and fetal cardiovascular adaptation, hypoxia does not yet exist as a
universal concept in which an index or a reference should be used. Hence, further
studies are necessary to standardize the conduct and, consequently, improve the perinatal
outcomes.[18]
The small number cases of FGR (n = 19, 4 early- and 15 late-onset) is a limitation of the present study. Early- and
late-onset FGR are two completely different entities; however, the main purpose of
the present study was assessing the correlation/agreement of maternal-fetal Doppler
parameters in normal and FGR fetuses. The approach to assess the maternal-fetal vessels
during the Doppler examinations was the same for both early- and late-FGR as well
as normal fetuses.
Conclusion
In summary, we observed a strong correlation between RI and PI UAt, UA, and MCA Doppler;
however, a weak agreement was observed between U/C and CPR in normal and FGR fetuses.
In SGA fetuses, the agreement between U/C and CPR was moderate.
