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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 5, September/October 2018
312
AFRICA
All the pre-eclamptic mothers were controlled on single
agents and none had magnesium sulphate therapy before our
examination. Steroids were not administered to the patients
at the time of the assessment. At least three measurements
were taken once a clear and consistent Doppler trace had
been obtained, and the measurement taken from the clearest
waveform was included in the final analysis.
Adverse obstetrical outcome later in the pregnancy was
defined as: development of significant oligohydramnios
(AFI
<
5 cm), antenatal decelerative cardiotocography, intra-
uterine death, development of imminent eclampsia or HELLP
(haemolysis, elevated liver enzymes and low platelet count)
syndrome, abruption placentae, and deterioration of foetal
Dopplers (arterial redistribution or venous Doppler anomalies).
We have previously documented high levels of inter- and intra-
observer variability agreement for the MPI and its components
in our article establishing reference intervals of the MPI in
normal pregnancies.
4
Statistical analysis
MPI values were transformed to
z
-scores using the standards
proposed by Bhorat
et al
.
4
Continuous variables are reported
as means with standard deviations for normally distributed
variables, and medians with interquartile ranges for variables
with skewed distributions. The Shapiro–Wilk test was used to
test for normality. The Wilcoxon rank sum test was used to
perform comparisons of the foetal parameters between the study
groups. To compare the adverse event rate and CPR categories
between the study groups, Fisher’s exact test was used.
The overall diagnostic accuracy of the MPI
z
-score for adverse
outcomes was assessed through computation of the area under
the receiver operating characteristics (ROC) curve. To determine
whether the MPI was an independent predictor of adverse
outcome, while adjusting for other foetal parameters, logistic
regression was used;
p
-values less than 0.05 were considered
statistically significant. All analysis was performed in Stata
version 14 (Stata Corp, College Station, TX, USA).
Results
A total of 55 subjects, comprising 32 IUGR cases, 11 PE-only
cases and 12 PE with IUGR cases (total PE cases: 23) were
included in the analysis. Controls were matched to cases in a 1:1
ratio by gestational age rounded off to the nearest week. The
mean gestational age in the controls, IUGR and any PE cases
was 31.4, 31.8 and 31.0 weeks, respectively.
The UA resistance index (UA RI) values were significantly
lower in the controls compared to the IUGR cases (
p
<
0.0001).
There was no significant difference in the median UA RI
between the controls and PE-only cases (
p
=
0.819). The amniotic
fluid index (AFI) was significantly higher in the controls
compared to the IUGR and PE-only group (
p
=
0.007 and 0.002,
respectively). MCA resistance index (MCA RI) values were
significantly higher in the controls compared to the IUGR-only
cases, however no significant difference was observed between
the controls and PE-only and PE–IUGR cases, respectively.
The lowest estimated foetal weight (EFW) was observed in the
IUGR cases, followed by the PE–IUGR cases. No significant
differences were observed between the EFW in the controls and
PE-only cases (
p
=
0.348).
The distribution of the standardised MPI values between the
groups of interest is presented in Table 1 and Figs 1 and 2. It is
clear that the distribution of MPI values was significantly lower
in the controls compared to all other groups. This is affirmed
by the analysis in Table 1, with all differences statistically
significant. The highest standardised MPI values were observed
in the PE–IUGR group, where a median of 5.62 was observed
(Fig. 2).
All foetal parameters were compared between the PE group
combined (
n
=
23) and IUGR cases (
n
=
32). The only significant
differences observed between these two groups was the UA (
p
=
0.01), where the IUGR cases tended to have higher UA values
compared to the combined PE group. Borderline statistical
significance was observed for the MCA values (
p
=
0.05) between
these groups.
The overall adverse event rate in the cases was 49%, which is
shown in Fig. 3 and Table 2. The highest rate was observed in
the PE–IUGR group where eight out of 12 (67%) experienced
adverse events. There was no significant difference in the adverse
event rate between the three groups (0.197).
Foetuses were also categorised according to their CPR
percentile for gestational age; 81, 9 and 58% were observed to
have CPR values less than the fifth percentile in the IUGR,
Table 1. Foetal parameters stratified by group
Parameters
Controls
(
n
=
55)
IUGR
(
n
=
32)
PE
(
n
=
23)
p
-value
any PE vs
IUGR
PE-only
(
n
=
11)
PE–IUGR
(
n
=
12)
p
-value
IUGR vs
controls
p-
value
PE-only vs
controls
p-
value
PE–IUGR
vs controls
UA
0.67
(0.66–0.69)
0.76
(0.745–0.79)
0.68
(0.66–0.75)
0.0108
0.67
(0.66–0.69)
0.715
(0.665–0.78)
<
0.0001
0.8189
0.0639
Gestation age (weeks),
mean (SD)
31.44
(1.88)
31.77
(1.65)
31.01
(1.90)
0.231
31.70
(1.53)
30.37
(2.04)
0.4079
0.6670
0.0831
MPI
0.38
(0.37–0.39)
0.535
(0.485–0.595)
0.50
(0.47–0.59)
0.3556
0.48
(0.45–0.49)
0.55
(0.50–0.60)
<
0.0001
<
0.0001
<
0.0001
MPI
z
-score
–0.01
(–0.38–0.38)
5.00
(4.37–5.58)
4.57
(4.07–6.32)
0.7200
4.29
(3.54–4.57)
5.62
(4.71–7.82)
<
0.0001
<
0.0001
<
0.0001
MCA
0.83
(0.82–0.86)
0.80
(0.78–0.83)
0.83
(0.80–0.86)
0.0538
0.83
(0.81–0.85)
0.82
(0.79–0.86)
0.0008
0.4940
0.2752
AFI
13
(12–14.5)
12.1
(10.7–13)
12
(11.1–13)
0.6944
11.8
(11.1–12.3)
12.65
(11.35–13.1)
0.007
0.0019
0.2324
EFW (mg)
2005
(1717–2210)
1561.5
(1344–1676)
1767
(1305–1989)
0.1105
1989
(1655–2012)
1600.5
(1076.5–1800.5)
<
0.0001
0.3482
0.0010
UA
=
umbilical artery, MPI
=
myocardial performance index, MCA
=
middle cerebral artery, AFI
=
amniotic fluid index, EFW
=
estimated foetal weight.
Data are reported as median (IQR) unless otherwise stated.