2
Fetal hemoglobin, 1-microglobulin and hemopexin are
predictive first trimester biomarkers for preeclampsia
3
Ulrik Dolberg Anderson1a,b*, Magnus Gram2, Jonas Ranstam3, Basky Thilaganathan4, Bo
4
Åkerström2 and Stefan R. Hansson1a,b
5
1a
6
University, Sweden
7
1b
8
2
Department of Clinical Sciences, Lund, Infection Medicine, Lund University, Sweden
9
3
Department of Clinical Sciences, RC Syd, Lund University, Sweden
10
4
Fetal Medicine Unit, St. George’s University of London, London, United Kingdom
1
Section of Obstetrics and Gynecology, Department of Clinical Sciences Lund, Lund
Skåne University Hospital, Malmö/Lund, Sweden
11
12
*Corresponding author:
13
[email protected]
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Department of Obstetrics and Gynecology
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University Hospital Skåne
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S-21466 Malmö, Sweden
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18
19
20
21
22
1
23
Abstract
24
Preeclampsia is a syndrome that complicates 3-8% of all pregnancies. Overproduction of cell-
25
free fetal hemoglobin in the preeclamptic placenta has been recently implicated as a new
26
etiological factor. In this study, maternal serum levels of cell-free fetal hemoglobin and the
27
endogenous hemoglobin/heme scavenging systems were evaluated as predictive biomarkers
28
for preeclampsia in combination with uterine artery Doppler ultrasound. The study was
29
designed as a case-control study including 433 women in early pregnancy (mean 13.7 weeks
30
of gestation) of which 86 subsequently developed. The serum concentrations of cell-free fetal
31
hemoglobin, total cell-free hemoglobin, the heme-scavenger hemopexin, the hemoglobin
32
scavenger haptoglobin and the heme- and radical-scavenger 1-microglobulin were measured
33
in maternal serum. All patients were examined with uterine artery Doppler ultrasound
34
pulsatility index and the presence of notching of the waveform was recorded. Logistic
35
regression models were developed, which included the biomarkers, ultrasound indices and
36
maternal risk factors. There were significantly higher serum concentrations of cell-free fetal
37
hemoglobin and 1-microglobulin and significantly lower serum concentrations of hemopexin
38
in patients who later developed preeclampsia. The uterine artery Doppler ultrasound results
39
showed significantly higher pulsatility index values in the preeclampsia group. The optimal
40
prediction model was obtained by combining cell-free fetal hemoglobin, 1-microglobulin
41
and hemopexin in combination with the maternal characteristics parity, diabetes and pre-
42
pregnancy hypertension. The optimal predicted rate for early and late preeclampsia combined
43
was 60 % with a 5% false positive rate. In summary, cell-free fetal hemoglobin in
44
combination with 1-microglobulin and/or hemopexin may be potential predictive serum
45
biomarkers for preeclampsia – either alone or in combination with maternal risk factors
46
and/or uterine artery Doppler ultrasound.
2
47
Introduction
48
Preeclampsia is a pregnancy-related condition affecting up to 8 % of pregnancies worldwide
49
[1]. The incidence varies according to geographical, social, economic and racial differences
50
[2]. It has been estimated that preeclampsia or complications of the condition account for
51
more than 50,000 maternal deaths worldwide each year [1].
52
Clinical manifestations appear after 20 weeks of gestation. Although the diagnostic criteria
53
are clear, [3] it has been difficult to find a way to predict the disease in early pregnancy or to
54
predict which women that will develop severe preeclampsia and/or eclampsia.
55
The details of the pathophysiology remain elusive but recent research has improved the
56
understanding of the condition markedly. Preeclampsia is described to develop in two stages
57
[4, 5]. The first stage is characterized by a defect placentation [6]. The extravillous
58
trophoblast cells do not remodel the spiral arteries in the maternal decidua properly and
59
consequently fail to create a low-resistance even utero-placental blood flow [6, 7]. Uneven
60
perfusion leads to oxidative stress in the placenta that contributes to the damage of the blood-
61
placenta barrier and subsequent leakage between the fetal and maternal circulation. In fact,
62
cell-free fetal DNA [8, 9], micro-particles [10] and cell-free fetal hemoglobin [11, 12] have
63
been described in the maternal circulation of women with preeclampsia [13, 14]. The second
64
stage of preeclampsia is characterized by the clinical manifestations, e.g. increased blood
65
pressure and proteinuria detected after 20 weeks of gestation [4, 5].
66
The link between the stages 1 and 2 is still a main focus of modern preeclampsia research.
67
Maternal constitutional factors such as obesity are important risk factors for late onset
68
preeclampsia in particular. Furthermore, a new focus area is the role of maternal cardiac strain
69
in the development of preeclampsia [14-17].
3
70
Results from gene- and proteome profiling studies have shown an over-production and
71
accumulation of cell-free fetal hemoglobin in the preeclamptic placenta [18]. Ex-vivo studies
72
using the dual-placental perfusion model have shown that cell-free hemoglobin causes
73
damage to the blood-placenta barrier and leakage of cell-free hemoglobin into the maternal
74
circulation [12, 19, 20]. Furthermore, cell-free fetal hemoglobin has been shown to appear
75
early in pregnancy in women who subsequently develop preeclampsia and has therefore been
76
suggested to be an important etiological factor and a potential biomarker for early detection of
77
preeclampsia [11, 12, 21-23]. In term pregnancies cell-free fetal hemoglobin was shown to
78
correlate to the severity of the disease, i.e. blood pressure [24].
79
Extracellular hemoglobin is in general toxic to tissues and organs [25, 26]. Hemoglobin and
80
its metabolites heme and free iron are particularly reactive and generate free radicals which
81
can cause cell- and tissue damage, oxidative stress, inflammation and vascular endothelial
82
damage [26]. The human system has evolved several different scavenging proteins that
83
protect the body from the toxicity of extracellular hemoglobin and heme. Haptoglobin, the
84
most well investigated human hemoglobin clearance system, binds cell-free hemoglobin in
85
the blood [26, 27]. The hemoglobin-haptoglobin complex subsequently bind to its receptor
86
CD163 [28] which eliminates it from the blood. Hemopexin is a circulating plasma protein
87
that is the major blood scavenger of free heme [29]. The hemopexin-heme complex is taken
88
up by cells such as macrophages and hepatocytes, expressing the CD91 receptor ,[25].
89
Previous in vitro results have indicated that decreased hemopexin activity may regulate blood
90
pressure through the renin-angiotensin-system in patients with preeclampsia [30, 31].
91
1-microglobulin is a plasma- and extravascular protein that provides protection through its
92
ability to bind and neutralize free heme and radicals [32-34]. Several in vitro and in vivo
93
studies have shown that 1-microglobulin protects cells and tissues in conditions with
94
increased burden of extracellular hemoglobin, heme and reactive oxidative species [24]. In
4
95
studies using liver- and placenta cells , 1-microglobulin expression has been shown to be up-
96
regulated following exposure to hemoglobin, heme and reactive oxygen species [24, 35].
97
Furthermore, the serum concentration of 1-microglobulin has also been shown to be
98
significantly elevated in maternal blood in the first trimester of patients who subsequently
99
develop preeclampsia [22].
100
In the last decade a number of predictive biomarkers have been described for preeclampsia.
101
Most of these markers reflect the placental pathology of preeclampsia and the pro-/anti-
102
angiogenetic imbalance. Some of the most well investigated markers are: Pregnancy
103
associated plasma protein A, placental protein 13, soluble endoglin, placental growth factor
104
and soluble FMS-like tyrosin kinase 1 (sFlt-1) [11, 21, 22, 36-43]. In order to increase the
105
sensitivity and specificity of the different markers, new algorithms have been developed that
106
include several of these markers [21, 23]. Furthermore, these algorithms combine biomarkers
107
with maternal risk characteristics such as parity, body mass index (BMI), maternal age,
108
systemic disorders and clinical parameters such as mean artery blood pressure. In addition,
109
uterine artery Doppler ultrasound can give an indication on the blood flow in the utero-
110
placental unit. Up to date, a number of algorithms have been suggested to predict
111
preeclampsia but none are yet broadly accepted for clinical use [21, 23].
112
The aim of this study was to analyze the serum concentrations of cell-free fetal hemoglobin
113
and the hemoglobin- and heme scavenging systems haptoglobin, hemopexin, and 1-
114
microglobulin in a larger cohort of uncomplicated pregnancies and pregnancies with
115
subsequent development of early-, late- and term onset preeclampsia.
116
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Materials and methods
5
118
Patients and samples
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The study was approved by the local ethical committees at St Georges University Hospitals,
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London, UK. All participants signed a written informed consent prior to inclusion. Women
121
attending a routine antenatal care visit at St. Georges Hospitals’ Obstetric Unit were recruited
122
from 2006 to 2008.
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The gestational length was calculated from the last menstrual period and confirmed by
124
ultrasound crown-rump-length measurement. Uterine artery Doppler ultrasound was
125
measured as previously described [44]. A maternal venous blood sample was collected at 6-20
126
weeks of gestation (mean 13.7 weeks) in a 5 mL vacutainer tube (Becton Dickinson, Franklin
127
Lakes, NJ, USA) without additives. After clotting, the samples were centrifuged at 2000xg at
128
room temperature (RT) for 10 minutes and serum was separated and stored at -80°C until
129
further analysis.
130
All pregnancy-outcome data was obtained from the main delivery suite database and checked
131
for each individual patient. Preeclampsia was defined according to ISSHP definitions as: 2
132
readings of blood pressure 140/90 mm Hg at least 4 hours apart, and proteinuria, 300mg in
133
24 hours, or 2 readings of at least +2 on dipstick analysis of midstream or catheter urine
134
specimens if no 24-hour urine collection was available [3]. Early onset preeclampsia was
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defined as preeclampsia with clinical manifestations before 34+0 weeks of gestation and late
136
onset preeclampsia was defined as clinical manifestations after 34+0 weeks of gestation.
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Term preeclampsia was defined as preeclampsia with clinical manifestations between 37+0 to
138
42+0 weeks of gestation. Normal uncomplicated pregnancy was defined as delivery at or after
139
37+0 weeks of gestation with normal blood pressure. The uncomplicated pregnancy samples
140
(controls) included in this study were randomly selected from samples collected during the
141
same period. Uncomplicated pregnancy was confirmed after delivery.
142
6
143
Measurement of cell-free fetal hemoglobin, 1-microglobulin, cell-
144
free total hemoglobin, haptoglobin and hemopexin
145
Cell-free fetal hemoglobin concentration in the serum samples was measured with a sandwich
146
ELISA as previously described [24]. Briefly, 96-wells plates were coated with affinity-
147
purified rabbit anti-cell-free fetal hemoglobin (4 µg/ml in PBS) overnight at RT. In the second
148
step, a standard series of cell-free fetal hemoglobin or the patient samples diluted in
149
incubation buffer were incubated for 2 hours at RT. In the third step, HRP-conjugated
150
affinity-purified rabbit anti-HbA antibodies, were added and incubated for 2 hours at RT.
151
Finally, a ready-to-use 3,3′,5,5′-Tetramethylbenzidine (TMB, Life Technologies, Stockholm,
152
Sweden) substrate solution was added. The reaction was stopped after 30 minutes using 1.0 M
153
HCl and the absorbance was read at 450 nm using a Wallac 1420 Multilabel Counter (Perkin
154
Elmer Life Sciences, Waltham, MA, USA).
155
The 1-microglobulin concentrations were determined by a radioimmunoassay (RIA) as
156
previously described (24). Briefly, RIA was performed by mixing goat antiserum against
157
human 1-microglobulin (“Halvan”; diluted 1:6000) with 125I-labelled 1-microglobulin
158
(appr. 0.05 pg/ml) and unknown patient samples or calibrator 1-microglobulin -
159
concentrations. After incubating overnight at RT antibody-bound antigen was precipitated
160
after which the 125I-activity of the pellets was measured in a Wallac Wizard 1470 gamma
161
counter (Perkin Elmer Life Sciences).
162
The concentration of total hemoglobin was determined with the Human Hemoglobin ELISA
163
Quantification Kit from Genway Biotech Inc. (San Diego, CA, USA). The analysis was
164
performed according to the manufacturer’s instructions and the absorbance was read at 450
165
nm using a Wallac 1420 Multilabel Counter.
166
The concentrations of haptoglobin in serum samples were determined using the Human
7
167
Haptoglobin ELISA Quantification Kit as described by the manufacturer (Genway Biotech
168
Inc.). The serum concentrations of hemopexin were determined using a Human Hemopexin
169
ELISA Kit as described by the manufacturer (Genway Biotech Inc.).
170
171
Statistical analysis
172
Statistical computer software IBM Statistical Package for the Social Sciences (SPSS
173
statistics) version 21.0 for Apple computers was used for all the analyses. A p value ≤ 0.05
174
was considered significant. Significant differences between the groups for the biomarkers
175
cell-free fetal hemoglobin, total hemoglobin, haptoglobin, hemopexin, and 1-microglobulin
176
were calculated with one-way ANOVA. The uterine artery Doppler ultrasound examination
177
was performed at a significantly later time point in pregnancies complicated by preeclampsia
178
compared to the control group and therefore the uterine artery Doppler ultrasound values were
179
transformed into Multiples of the Median (MoM)-values according to median values given by
180
Velauthar et al [45].
181
The prediction models based on the biomarkers and maternal characteristics were built on
182
stepwise logistic regression. Separate analyses were performed for early onset preeclampsia
183
and late onset preeclampsia. Receiver operation curves (ROC-curves) were obtained for all
184
regression parameters and the parameters in combination. Their sensitivities at different
185
specificity levels were calculated and optimal sensitivity/specificity was defined as the point
186
closest to the upper left corner in the ROC-curve.
187
188
Results
189
Demographics
190
In total, 433 women were included of which 86 subsequently developed preeclampsia. As
8
191
controls, 347 women with uncomplicated pregnancies and term delivery (>37 weeks of
192
gestation) were included. The maternal characteristics are shown in Table 1. Of the 86
193
preeclamptic cases, 28 were delivered before 37+0 weeks of gestation and17 delivered before
194
34+0 weeks of gestation. There was no statistically significant difference between the case
195
and control groups in terms of time of serum sampling.
196
There was a statistically significant difference in ethnicity in the control group as compared to
197
the preeclampsia group DESCRIBE!. The preeclampsia group showed significantly higher
198
pregnancy/parity rate compared to the control group. The BMI was significantly higher in the
199
preeclampsia group compared to the control group. The uterine artery Doppler ultrasound
200
examination was performed at a significantly later time point in pregnancies complicated by
201
preeclampsia compared to the control group (mean gestation of 18.5 weeks in the
202
preeclampsia group vs. 12.5 weeks of gestation in the control group, p=0.0001). The birth
203
weight was significantly lower in the preeclampsia group as compared to the control group.
204
There were significantly more preterm deliveries in the preeclampsia group as compared to
205
the control group. Furthermore, diabetes was diagnosed in three preeclampsia patients
206
whereas none of the women in the control group was diagnosed with diabetes.
207
208
Biomarkers
209
The serum levels of the biomarkers cell-free fetal hemoglobin, haptoglobin, hemopexin, 1-
210
microglobulin and total hemoglobin are shown in Table 2. The mean concentration of cell-
211
free fetal hemoglobin in the preeclampsia group was significantly higher than in the control
212
group (10.8 μg/ml vs. 5.6 μg/ml, p=0.02). The mean 1-microglobulin concentration was also
213
significantly increased (17.3 μg/ml vs. 15.5 μg/ml, p=0.03). The mean hemopexin
214
concentration in the preeclampsia group was significantly lower (1062 μg/ml vs. 1143 μg/ml
215
in the control group p=0.05). There was a higher haptoglobin concentration in the
9
216
preeclampsia group (1102 g/ml) as compared to the control group (971 g/ml), however this
217
was not significant (p=0.089). The uterine artery Doppler ultrasound MoM values were
218
significantly higher in the preeclampsia group than the controls (1.18 vs. 0.95, p<0.0001).
219
220
Logistic regression analysis
221
Despite a significantly increased serum cell-free fetal hemoglobin concentration in patients
222
who subsequently developed preeclampsia (Table 3, Figure 1 and 2), it displayed limited
223
predictive value when used alone (sensitivity 15% at 90% specificity). 1-microglobulin
224
showed a similar prediction (sensitivity of 19% at 90% specificity). In combination however
225
the biomarkers 1-microglobulin, cell-free fetal hemoglobin, and hemopexin performed better
226
(33% sensitivity and 90% specificity).
227
All measures of maternal characteristics were tested alone and in combination using a logistic
228
regression analysis to compare preeclampsia and controls. Furthermore, the biophysical
229
parameters obtained from the uterine artery Doppler ultrasound (PI left, PI right, PI mean,
230
diastolic notch right and left) were also evaluated in the logistic regression analysis. The
231
maternal characteristics, i.e. ethnicity, number of previous pregnancies (gravidae), number of
232
previous deliveries (parity), maternal BMI, maternal diabetes and maternal hypertension,
233
were each significantly associated to the development of preeclampsia in the logistic
234
regression analysis. In the combined logistic regression model however, the combination of
235
maternal ethnicity, BMI, diabetes and hypertension were the only parameters that
236
significantly altered the sensitivity. All the maternal characteristics in combination showed a
237
60% sensitivity and 90% specificity (Table 3, Figure 2). The Uterine artery Doppler
238
ultrasound parameters alone showed similar prediction to the biomarkers alone (25%
239
sensitivity and 90% specificity).
240
The combination of maternal characteristics (parity, diabetes, pre-pregnancy hypertension)
10
241
and the biomarkers (cell-free fetal hemoglobin, 1-microglobulin and hemopexin) increased
242
the sensitivity to 62% at 90% specificity (Table 3, Figure 2) and the combination of uterine
243
artery Doppler ultrasound values and maternal characteristics combined showed a similar but
244
lower prediction rate (57% sensitivity and 90% specificity). However, the combination of
245
biomarkers, maternal characteristics and uterine artery Doppler ultrasound values did not
246
show higher prediction rates (53% sensitivity and 90% specificity) than the combinations
247
uterine artery Doppler ultrasound/ biomarkers-, biomarkers/maternal characteristics- or
248
uterine artery Doppler ultrasound/ maternal characteristics - combinations (Table 3).
249
250
Early-, late- and term-onset preeclampsia
251
The results showed elevated levels of cell-free fetal hemoglobin in both early- late- and term-
252
onset preeclampsia groups (Table 4). The 1-microglobulin levels were only significantly
253
higher in the late and term onset groups (p=0.01 and p=0.016) (Table 4). The hemopexin
254
protein concentration was lower in all groups as compared to the controls, but only
255
statistically significant in early onset preeclampsia (p=0.04)(Table 4). The uterine artery
256
Doppler ultrasound PI MoM was significantly elevated, especially in the early onset group
257
(1.63 vs. 0.95, p<0.00001). It was only marginally elevated in the late onset group and not
258
statistically significant (1.06 vs. 0.95, p=0.06). In the term preeclampsia group there was only
259
a marginally elevated uterine artery PI, which did not reach statistical significance (p=0.35).
260
There were no significant differences for total hemoglobin or haptoglobin in either of the
261
study groups.
262
The logistic regression models for early-, late- and term-onset preeclampsia showed 23%
263
prediction rate for cell-free fetal hemoglobin at 90% specificity in the late onset preeclampsia
264
group (Table 5) and 19% sensitivity at 90% specificity in term preeclampsia1-microglobulin
265
was significantly elevated in the late- and term onset groups (24% sensitivity at 90%
11
266
specificity, p=0.003). Hemopexin was only statistically significantly decreased in the early
267
onset group and showed 32% sensitivity at 90% specificity. The Uterine artery Doppler
268
ultrasound values performed best in the early onset group, 57% sensitivity at 90% specificity
269
but was even statistically significant in the late onset group (p=0.025 (this p-value only
270
applies to the logistic regression analysis), however not in the term onset group (p=0.36).
271
None of the biomarkers were statistically significant when combined with each other, with
272
maternal characteristics or with uterine artery Doppler ultrasound values in either of the
273
preeclampsia subgroups.
274
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275
Discussion
276
The main finding in this paper confirms that both cell-free fetal hemoglobin and 1-
277
microglobulin are significantly elevated in first trimester serum in women who subsequently
278
developed preeclampsia (Table 2)[22] and that they have the potential of being used as
279
predictive first and early second trimester biomarkers for preeclampsia. Furthermore, the
280
heme scavenging plasma protein hemopexin also showed predictive properties and was
281
therefore suggested as an additional potential first trimester biomarker for preeclampsia. The
282
uterine artery Doppler ultrasound indices primarily showed higher PI MoM values in the early
283
onset group. This is in full concordance with previously published results [21, 45].
284
Even though cell-free fetal hemoglobin, 1-microglobulin and hemopexin showed predictive
285
ability as individual biomarkers, there was only a weak additional value when they were
286
combined in the logistic regression models. This could be due to the fact that they are
287
biologically linked to each other and therefore predict the clinical outcome in the same way.
288
The optimal prediction model contained cell-free fetal hemoglobin, 1-microglobulin and
289
hemopexin in combination with the maternal characteristics parity, diabetes and pre-
290
pregnancy hypertension.
291
Compared to previously published results, the prediction capacity of these biomarkers is
292
weaker [22]. The current cohort however, better reflects a normal population with fewer
293
preeclampsia cases, which clearly influences the results. The results presented do however
294
need to be confirmed in a cohort with normal (<8%) prevalence of preeclampsia.
295
In contrast to this, the maternal characteristics were found to have a high prediction capacity,
296
60% sensitivity at 90% specificity (Table 3). Comparable data from previously published
297
studies containing several additional parameters show sensitivity values of approximately
13
298
46% at 90% specificity for early onset preeclampsia [21]. The use of maternal characteristics
299
as prediction tool in a clinical setting is simple but requires software to calculate the patients’
300
risks. The advantage of a prediction model solely based on biomarkers is the fixed cut off
301
value for indication of high-risk.
302
Doppler ultrasound indices have been used in several first trimester prediction algorithms.
303
Significantly higher PI and notching in patient who subsequently develop preeclampsia or
304
IUGR have been shown at the end of the first trimester [46]. However, at this early stage of
305
pregnancy the placenta is not fully developed and high PI and presence of diastolic notching
306
could be physiological. After 18-20 weeks of gestation, when the placenta is fully developed,
307
the remodeling of the maternal spiral arteries have been completed and the resistance in the
308
uterine arteries are lower - clinically indicated by lower PI. Persistent high PI and notching is
309
therefore considered a pathological sign after this time point in pregnancy. In the present
310
study there was a significant difference regarding when in the pregnancy the uterine artery
311
Doppler ultrasound values were obtained, earlier for the controls (mean gestation of 12.4
312
weeks) than for the preeclampsia group (mean gestation of 18.5 weeks). Since uterine artery
313
resistance is known to decrease progressively during pregnancy, transformation of the values
314
to MoM-values was needed. In a perfect setting the cohort would have enough controls to
315
make a normal PI median-values for each week of gestation. With a mean PI MoM of 0.95 in
316
the control group it seems fair to use these previously published normal values to normalize
317
our PI values. A disadvantage of using Doppler examination is that it requires expensive
318
equipment and trained personnel. A biomarker model in combination with maternal
319
characteristics would therefore be preferable for clinical implementation in developing
320
countries.
321
Several studies indicate differences in disease mechanisms for early- and late onset
322
preeclampsia [21, 37, 39, 47]. To study the role of cell-free fetal hemoglobin and its toxicity
14
323
in relation to the onset of the clinical manifestations, the cohort was subdivided into early-,
324
late- and term onset preeclampsia. All the preeclampsia-groups showed significantly
325
increased serum levels of cell-free fetal hemoglobin. The concentration was highest in the
326
early onset preeclampsia group. We have previously suggested that 1-microglobulin
327
concentrations rise as a response to increased cell-free fetal hemoglobin levels [22, 24], which
328
is supported by the current findings for late- and term onset preeclampsia (Table 4) [22, 24].
329
A higher concentration of cell-free fetal hemoglobin was seen in early onset- compared to late
330
onset preeclampsia. This suggests that a consumption of the hemoglobin- and heme-
331
scavenging proteins takes place and may explain the lower levels of hemopexin in the early
332
onset group where HbF levels were highest (Table 4). Most prediction algorithms that are
333
based on placental and angiogenic markers such as pregnancy associated plasma protein A,
334
placental growth factor and sFlt-1, mostly in combination with uterine artery Doppler
335
ultrasound, primarily predict early onset [21, 43, 47-50]. The biomarkers presented in this
336
study show potential to also be able to predict late onset preeclampsia, which may be
337
clinically useful to determine when to terminate the pregnancy.
338
339
It has often been suggested that several different pathologies could lead to the clinical
340
manifestations that define preeclampsia, hypertension and proteinuria. Generally, early onset
341
preeclampsia more often presents with placenta pathology and IUGR whereas late onset
342
preeclampsia is more dependent on maternal constitutional factors. Assuming that
343
overproduction of cell-free fetal hemoglobin occurs in both types of preeclampsia, it is more
344
likely that an early onset preeclampsia will deplete the protective scavenger systems early in
345
pregnancy, i.e. presenting with lower concentrations of scavengers as shown for hemopexin in
346
the early onset preeclampsia group (Table 4).
15
347
It was however not possible to predict all preeclampsia patients with the current set of
348
biomarkers. As a consequence it can be assumed that not all preeclamptic patients have a
349
defect placental hematopoiesis. An ideal algorithm for the prediction of preeclampsia should
350
therefore contain biochemical markers that reflect several types of pathology (placental or
351
maternal) and maybe be combined with biophysical markers that reflect different parts of the
352
pathophysiological cascades seen in preeclampsia [21, 23].
353
354
355
Conclusions
356
Cell-free fetal hemoglobin and 1-microglobulin concentrations are elevated in maternal
357
serum at the end of first trimester in patients who subsequently develop preeclampsia.
358
Maternal serum levels of cell-free fetal hemoglobin, 1-microglobulin and hemopexin are
359
potential predictive biomarkers for subsequent development of both early- and late-onset
360
preeclampsia. Furthermore, combining these biomarkers with uterine artery Doppler
361
ultrasound and/or maternal characteristics, further increases the sensitivity and specificity of
362
preeclampsia screening.
363
364
365
366
367
16
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References
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Figure legends
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Figure 1: Receiver operation curves of cell-free fetal hemoglobin, 1-microglobulin,
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haptoglobin and Doppler ultrasound PI as predictive biomarkers of all preeclampsia cases. All
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biomarkers are presented with area under the ROC-curve (AUC). Specific values are found in
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Table 3.
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Figure 2: Receiver operation curves of the maternal characteristics, the combination of
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biomarkers, biomarkers combined with Doppler ultrasound and maternal characteristics
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combined with biomarkers. All biomarkers are presented with area under the ROC-curve
518
(AUC). Specific values are found in Table 3.
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