Evidence of an Imbalance of Angiogenic/Anti-angiogenic Factors in Massive Perivillous Fibrin Deposition (Maternal Floor Infarction): a Placental Lesion associated with Recurrent Miscarriage and Fetal Death

Abstract

Objective

Massive perivillous fibrin deposition (MPFD) is associated with serious complications of pregnancy including recurrent spontaneous abortion, fetal growth restriction and fetal demise. The aim of the study was to determine if maternal plasma concentrations of angiogenic/anti-angiogenic factors in MPFD differ from uncomplicated pregnancies.

Study Design

This retrospective longitudinal case-control study included MPFD cases (n=10) and control patients (n=175) with uncomplicated pregnancies who were enrolled in a longitudinal study and delivered at term. Serial plasma concentrations of placental growth factor (PlGF), soluble endoglin (sEng), and soluble vascular endothelial growth factor receptor (sVEGFR) -1 and -2 were determined by ELISA (cases, n=28 samples; controls, n=751 samples). Individual analyte concentrations were averaged across gestational length at specimen collection intervals. Linear mixed models were used to test for differences in log transformed mean analyte concentrations both overall and as a function of time.

Results

1) Patients with MPFD had a lower mean plasma PlGF concentration (p=0.03) and higher mean plasma concentrations of sVEGFR-1 and sEng (both p<0.01) than controls, adjusted for potential confounders; 2) the mean plasma concentration of PlGF differed further among cases and controls as a function of gestational age interval (p<0.0001); however, mean sVEGFR-1 and sEng group differences as a function of gestational age interval approached but did not reach significance (p=0.09, p=0.11, respectively); 3) patients with MPFD had lower mean plasma concentrations of PlGF/sVEGFR-1 (p<0.0001) and PlGF/sEng (p<0.001); both of these relationships differed further as a function of gestational age interval (both p<0.0001); and 4) differences in mean sVEGFR-1, sEng, and the ratios of PlGF/sVEGFR-1 and PlGF/sEng were observed before 20 weeks of gestation.

Conclusion

An imbalance of angiogenic/anti-angiogenic factors is present in patients with MPFD prior to the diagnosis. We propose that these changes participate in the mechanisms responsible for adverse pregnancy outcomes in patients with MPFD.

Introduction

Massive perivillous fibrin deposition (MPFD), also known as “maternal floor infarction” (MFI), is characterized by obliteration of the villous trophoblast with extensive deposition of fibrinoid material in the intervillous space.¹ This condition was first described by Benirschke and Driscoll in 1967 and its frequency is 0.09-0.5%.^1-4 MPFD is associated with recurrent serious adverse pregnancy outcomes including spontaneous abortion,^{1, 5} fetal growth restriction,^{1, 2, 4, 6-12} and fetal death.^{2, 4-7, 10, 11, 13-16} The proposed etiologies include autoimmunity (such as anti-phospholipid^{6, 10, 11} or anti-urokinase antibodies)⁶ and cytotoxicity due to proliferation of “X-cells” which are extravillous trophoblasts that can produce major basic protein similar to that of eosinophil granules.¹² However, the precise mechanisms leading to MPFD are unknown.

Angiogenesis, the development of new blood vessels from preexisting vasculature, is crucial for fetal growth and placental development.^17-19 Successful pregnancy requires a balance between angiogenic and anti-angiogenic factors.^20-25. A growing body of evidence suggests that an imbalance of angiogenic/anti-angiogenic factors is involved in the pathophysiology of preeclampsia (PE),^26-70 pregnancies with small-for-gestational-age neonates (SGA),^{28, 30, 33, 41, 71-77} spontaneous preterm labor and delivery,^78-80 stillbirth,^81-83 mirror syndrome,^84-88 twin to twin transfusion syndrome,^{89, 90} and molar pregnancies.^91,92 Moreover, changes in the concentrations of the angiogenic factor, placental growth factor (PlGF) and anti-angiogenic factors, soluble vascular endothelial growth factor receptor (sVEGFR)-1 and soluble endoglin (sEng) in maternal circulation, precede the clinical diagnosis of PE,^{30, 33, 34, 41, 43, 48, 55, 58, 62, 93} SGA^{30, 41, 72} and stillbirth.⁸³ Since the clinical presentation of MPFD includes conditions associated with derangements of angiogenic and anti-angiogenic factors, it is possible that an anti-angiogenic state may play a role in the genesis of MPFD.

The objective of this study was to determine if pregnancies with MPFD have alterations in maternal plasma concentrations of PlGF, sEng, sVEGFR-1 and sVEGFR-2 before the diagnosis of the condition.

Materials and Methods

Study Design and Patient Selection

A longitudinal retrospective case-control study was conducted by reviewing placenta pathology records in our institution from 2006 to 2011. Cases consisted of patients with placental pathology meeting the diagnostic requirements for MPFD, which was defined as a placenta with perivillous fibrinoid material (either limited to the maternal floor of the placenta or extending from maternal to fetal surfaces) encasing at least 50% of the villi on a minimum of one slide. Controls were women without MPFD in the placenta, who had uncomplicated pregnancies, delivered a term neonate whose birth weight was appropriate for gestational age (10^th - 90^th percentiles)⁹⁴ and had plasma samples available for at least five of the following gestational age intervals: 6-9.9, 10-14.9, 15-19.9, 20-23.9, 24-27.9, 28-31.9, 32.-36.9 and ≥37 weeks. These patients were enrolled in a longitudinal protocol to identify biological markers for the prediction of PE, SGA, and stillbirth. Venous samples were collected every 4 weeks until 24 weeks and every 2 weeks thereafter until delivery. Exclusion criteria were 1) multiple gestations and 2) congenital fetal anomaly.

All women provided written informed consent before participating in the study and the use of clinical data and collection and utilization of biological samples for research purposes were approved by the Institutional Review Boards of Wayne State University and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of health, U.S. Department of Health and Human Services.

Sample Collection and Immunoassays

Venipuncture was performed serially at regular prenatal visits and admissions to the hospital for all normal and MPFD affected pregnancies. Blood was collected into tubes containing EDTA. Samples were centrifuged and stored at -70° C until used for assay. Sensitive and specific immunoassays (R&D systems, Minneapolis, MN) were used to determine maternal plasma concentrations of PlGF, sEng, sVEGFR-1 and -2. All immunoassays utilized the quantitative sandwich enzyme immunoassay technique, and their concentrations in maternal plasma were determined by interpolation from the standard curves. The inter- and intra-assay coefficients of variation (CV) obtained in our laboratory were as follows: PlGF, 6.02 and 4.8%, respectively; s-Eng, 2.3 and 4.6%, respectively; sVEGFR-1, 1.4 and 3.9%, respectively; and sVEGFR-2, 2 and 4%, respectively. The sensitivity of the assays was as follows: PlGF, 9.52 pg/mL; s-Eng, 0.08 ng/mL; sVEGFR-1, 16.97 pg/mL; and sVEGFR-2, 19.01 pg/mL.

Statistical Analysis

Demographic and obstetrical characteristics

Comparisons between continuous variables were performed by Mann-Whitney U tests. Proportions were compared using either Fisher exact or Chi-square tests as appropriate. A p-value <0.05 was considered statistically significant. Descriptive analysis was performed using SPSS Version 15.0 (SPSS, Inc., Chicago, IL, USA).

Longitudinal analysis of angiogenic/anti-angiogenic factor concentrations

Individual analyte concentrations (PlGF, sEng, sVEGFR-1, and sVEGFR2) and their ratios (PlGF/sEng and PlGF/sVEGFR-1) were averaged across four intervals defined by gestational length at venipuncture (<14 weeks, 14-16 weeks, 17-19 weeks, and 20-30 weeks). Linear mixed models were used to test for differences in log₁₀ transformed mean analyte concentrations overall and as a function of time using a robust covariance matrix estimator. Covariables included in adjusted models were selected based on clinical knowledge and factors associated with MPFD and/or analyte concentrations. These included gestational age at venipuncture, body mass index (BMI), maternal age, African American ethnicity and nulliparity. Model reduction was additionally performed based on the plausibility of regression coefficients, association with independent/dependent varbles, magnitude of change in the main effect parameter estimates⁹⁵ and model fit as indicated by the Bayesian Information Criteria (BIC)⁹⁵. Linear combinations of model parameters comparing differences between cases and controls at each gestational age interval were used to determine the timing of changes in angiogenic/anti-angiogenic factors. Longitudinal analyses were performed using SAS version 9.3 (SAS Institute Inc, Cary, NC, USA).

Results

Clinical Characteristics

During the study period, 10 pregnancies with MPFD and 175 controls were identified. Table 1 describes the clinical and demographic characteristics of the study population. As expected, the median gestational age at delivery and the median birthweights were lower in the MPFD affected pregnancies than those in uncomplicated pregnancies (each p < 0.001; see Table 1). Pregnancy complications in cases with MPFD included miscarriage in the second trimester (n= 4), fetal growth restriction (n=4) with abnormal umbilical artery Doppler velocimetry (n=3), second and third trimester fetal demise (in-utero: n=5; intrapartum: n=1), and abruptio placentae (n=2). With the exception of one patient who delivered at term, all MPFD cases delivered before 31 weeks of gestation and only two had viable neonates (see Table 2). Three pregnancies have been evaluated for the presence of anticardiolipin antibody and lupus anticoagulant and all of these tests were negative.

Table 1. Demographics and clinical characteristics of the study population.

	Uncomplicated pregnancies (n=175)	MPFD (n=10)	p-value
Maternal Age (years)	23 (20-26)	31 (26-35)	<0.001
African American	151 (86%)	10 (100%)	0.4
Nulliparity	63 (35%)	0 (0%)	0.03
BMI (kg/m2)	27 (23-32)	29 (28-35)	0.04
Gestational Age at Delivery (weeks)	39 (39-40)	23 (17-29)	<0.001
Birth weight (grams)	3330 (3150-3555)	277 (175-605)	<0.001
Stillbirth (> 20 weeks)	0	4 (40%)	---
Miscarriage in the Second Trimester (<20 weeks)	0	4 (40%)	---
Fetal Growth Restriction	0	4 (40%)	---
Placental Abruption	0	2 (20%)	---

Data are expressed as median (interquartile range) or number (percent).

MPFD: Massive perivillous fibrin deposition

BMI: Body mass index

Table 2. Clinical and obstetrical characteristics of patients with massive perivillous fibrin deposition.

Case Number	Age	Gravida, Parity	Gestational age at delivery (weeks+days)	Clinical Description	Birth Weight (grams, percentile for GA)	Prelabor Rupture of Membranes	Fetal Growth Restriction	Fetal Demise	Second Trimester Miscarriage
1	24	G 4 P 2-0-1-2	15+6	Presented with ruptured membranes and was induced for inevitable abortion.	150	Yes	No	No	Yes
2	27	G 3 P 0-0-2-0	30+0	Presented with fetal growth restriction, heavy vaginal bleeding/clinical placental abruption and emergent cesarean delivery was performed.	755(1%)	no	Yes	No	No
3	22	G 2 P 0-0-1-0	22+3	Short cervix was noted at 20 weeks; membranes ruptured with spontaneous labor at 22 weeks and delivery of a stillborn infant.	448 (34%)	Yes	No	Yes	No
4	28	G 11 P 0-1-9-1	23+6	Fetus noted to have thickened placenta, multiple placental lacunae, and oligohydramnios at 18 weeks; abnormal Doppler parameters, fetal demise was diagnosed and the patient was induced	277 (1%)	No	Yes	Yes	No
5	43	G 13 P 3-3-6-4	16+4	Presented with ruptured membranes and fetal demise.	Unknown	Yes	No	Yes	Yes
6	35	G 7 P 0-0-6-0	17+3	Cervical length of 0 mm on routine scan; A rescue cerclage was placed but membranes ruptured shortly afterwards. Induction for inevitable abortion.	160	Yes	No	No	Yes
7	29	G 3 P 1-1-0-1	17+2	Presented with abdominal pain and vaginal bleeding. Fetal demise was diagnosed and the patient was induced.	190	No	No	Yes	Yes
8	35	G 12 P 8-2-1-8	23+1	Fetus noted to have decreased growth and progressive deterioration of Doppler parameters starting at 20 weeks gestation. Fetal demise diagnosed at 23 weeks.	274 (1%)	No	Yes	Yes	No
9	34	G 11 P 8-1-1-8	28+2	Fetus noted to have growth restriction and progressive deterioration of Doppler parameters starting at 20 weeks. Fetal demise diagnosed and the patient was induced.	454 (1%)	No	Yes	Yes	No
10	33	G 10 P 7-1-1-7	38+1	Spontaneous labor at term.	3285 (51.5%)	No	No	No	No

^**Cases #8-10 are pregnancies from the same patient; GA=gestational age; G=gravida; P=parity

Longitudinal analysis of plasma sVEGFR-1, sVEGFR-2, sEng, and PlGF concentrations

Patients with MPFD had a significantly lower mean plasma PlGF concentration (p=0.03), but significantly higher mean plasma concentrations of sVEGFR-1 (p<0.01) and sEng (p<0.01) than controls after adjusting for potential confounders (see Figures 1 and 2). The mean maternal plasma concentrations of PlGF differed further among patients who had MPFD and the control group as a function of gestational age interval (p<0.0001). However, the magnitude of the differences in mean plasma concentrations of sVEGFR-1 and sEng did not change significantly with gestational age interval (p=0.09, Figure 1; p=0.11, Figure 2). There were no significant differences in plasma concentrations of sVEGFR-2 observed overall (p=0.97), or as a function of time (p=0.17) among cases and controls (see Figure 3).

Figure 1. Estimated mean +/- standard error of plasma concentrations (log10) of PlGF (1A) and sEng (1B) in MPFD and uncomplicated pregnancies by gestational age interval.

Estimated mean PlGF concentrations over time are adjusted by gestational age at venipuncture and body mass index; Estimated mean sEng concentrations over time are adjusted by gestational age at venipuncture, African American ethnicity and nulliparity; P-values reflect the group differences in estimated mean concentrations overall, as a function of gestational age interval, and at each gestational age interval determined by the linear mixed effects model.

Figure 2. Estimated mean +/- standard error of plasma concentrations (log10) of sVEGFR-1 in MPFD and uncomplicated pregnancies by gestational age interval.

Estimated mean sVEGFR-1 concents over time are adjusted by gestational age at venipuncture and maternal age; P-values reflect the group differences in estimated mean concentrations overall, as a function of gestational age interval, and at each gestational age interval determined by the linear mixed effects model.

Figure 3. Estimated mean +/- standard error of plasma concentrations (log10) of sVEGFR-2 in MPFD and uncomplicated pregnancies by gestational age interval.

Estimated mean sVEGFR-2 concentrations over time are adjusted for effects of gestational age at venipuncture, body mass index, and African American ethnicity; P-values reflect the group differences in estimated mean concentrations overall, as a function of gestational age interval, and at each gestational age interval determined by the linear mixed effects model.

Patients with MPFD had significantly lower mean ratio concentrations of PlGF/sVEGFR-1 (p<0.0001) and PlGF/sEng (p<0.001; Figure 4) after adjustment for potential confounders; both of these relationships differed significantly as a function of gestational age interval (each p<0.0001; Figure 4).

Figure 4. Estimated mean +/- standard error of plasma concentrations (log10) in the Ratios of PlGF/sVEGFR-1 (1A) and PLGF/sEng (1B) in MPFD and uncomplicated pregnancies by gestational age interval.

Estimated mean PlGF/sVEGFR-1 concentration ratios over time are adjusted for gestational age at venipuncture, body mass index, and nulliparity; Estimated mean PlGF/sVEGFR-1 concentration ratios over time are adjusted for gestational age at venipuncture, African American ethnicity, and body mass index; P-values reflect the difference in estimated mean concentrations at each gestational age interval determined by the linear mixed effects model.

As shown in Figures 1-4, while the differences in mean plasma PlGF concentration among cases and controls became statistically significant at 20-30 weeks of gestation, differences in mean sEng and the ratios of PlGF/sEng and PlGF/sVEGFR-1 among cases and controls became significant from 17-19 weeks of gestation onwards. Consistent changes in the mean plasma sVEGFR-1 concentration in cases compared to controls appear to begin early, at 14-16 weeks gestation. The mean concentration of each angiogenic and anti-angiogenic factor for each gestational age interval in MPFD patients and controls are shown in Table 3.

Table 3. Mean, standard deviation, median and inter-quartile range plasma analyte concentrations and their ratios by study group and gestational length interval at measurement.

Analyte	Gestational Length Interval	Study Group	N*	Mean	Std. Dev.	Median	25th centile	75th centile
PlGF(pg/mL)	I: <14 weeks	Case	4	20	7	22	16	24
		Control	110	40	98	23	16	36
	II: 14-16 weeks	Case	7	106	45	119	76	152
		Control	82	106	61	87	59	132
	III: 17-19 weeks	Case	4	110	63	126	73	148
		Control	72	201	106	189	125	260
	IV: 20-30 weeks	Case	6	125	103	100	43	206
		Control	172	598	409	516	320	775
sEng (ng/mL)	I: <14 weeks	Case	4	20	7	22	16	24
		Control	110	40	98	23	16	36
	II: 14-16 weeks	Case	7	106	45	119	76	152
		Control	82	106	61	87	59	132
	III: 17-19 weeks	Case	4	110	63	126	73	148
		Control	72	201	106	189	125	260
	IV: 20-30 weeks	Case	6	125	103	100	43	206
		Control	172	598	409	516	320	775
sVEGFR-1 (pg/mL	I: <14 weeks	Case	4	2200	1165	2487	1510	2891
		Control	110	1697	1276	1513	986	1930
	II: 14-16 weeks	Case	7	2972	1439	3006	1305	4102
		Control	82	1912	1022	1661	1249	2355
	III: 17-19 weeks	Case	4	4955	2961	5664	2799	7111
		Control	72	2276	2707	1737	1295	2660
	IV: 20-30 weeks	Case	6	28526	56386	4209	1695	16377
		Control	172	2092	1610	1727	1173	2456
sVEGFR-2 (ng/mL)	I: <14 weeks	Case	4	10.3	1.4	10.2	9.2	11.5
		Control	110	10.1	2.0	9.9	8.8	11.1
	II: 14-16 weeks	Case	7	10.7	1.7	11.1	9.7	11.8
		Control	82	10.3	1.8	10.2	9.0	11.2
	III: 17-19 weeks	Case	4	11.2	1.3	11.1	10.2	12.3
		Control	72	10.6	1.9	10.3	9.3	12.0
	IV: 20-30 weeks	Case	6	9.9	2.5	10.5	7.6	11.9
		Control	172	10.9	2.0	10.7	9.7	12.2
PlGF/sEng (pg/ng)	I: <14 weeks	Case	4	2.4	0.7	2.4	1.8	2.9
		Control	110	5.9	13.7	3.7	2.6	5.2
	II: 14-16 weeks	Case	7	14.1	7.3	14.3	5.6	20.6
		Control	82	16.6	9.0	14.2	9.7	22.2
	III: 17-19 weeks	Case	4	11.8	8.2	11.7	6.1	17.6
		Control	72	34.1	17.4.	33.6	21.3	49.2
	IV: 20-30 weeks	Case	6	14.1	15.2	9.8	1.2	23.7
		Control	172	1024	67.8	98.1	55.3	125.4
PlGF/sVEGFR-1	I: <14 weeks	Case	4	0.01	0.01	0.01	0.01	0.02
		Control	110	0.02	0.03	0.02	0.01	0.03
	II: 14-16 weeks	Case	7	0.04	0.03	0.03	0.03	0.03
		Control	82	0.07	0.04	0.06	0.03	0.09
	III: 17-19 weeks	Case	4	0.02	0.00	0.02	0.02	0.03
		Control	72	0.13	0.11	0.10	0.07	0.15
	IV: 20-30 weeks	Case	6	0.04	0.05	0.03	0.00	0.05
		Control	172	0.36	0.30	0.29	0.19	0.42

Note:

^*N= number of patients, not samples; PlGF= placental growth factor, sEng = soluble endoglin, sVEGFR-1= soluble vascular endothelial growth factor receptor-1

Comment

Principal Findings

Patients who developed MPFD had 1) a significantly lower mean plasma concentration of PlGF than controls at 20-30 weeks of gestation; 2) a higher mean plasma concentration of sVEGFR-1 than the control group from 14-16 weeks of gestation; and 3) a higher mean sEng concentration, but a lower mean PlGF/VEGFR-1 ratio and PlGF/sEng ratio concentration, than those with uncomplicated pregnancies starting from 17-19 weeks onwards.

MPFD was originally described as a pathologic finding characterized by increased fibrinoid material surrounding trophoblastic villi.^{3, 14} Subsequently, Katzman and Genest proposed to subdivide this pathologic condition into 3 categories: 1) maternal floor infarction (MFI); 2) transmural MPFD; and 3) borderline MPFD.¹ The diagnosis of MPFD in the current study required the identification of fibrinoid material encasing at least 50% of the villi on a minimum of one slide, and included either cases with fibrinoid material only on the maternal floor of the placenta or cases with transplacental fibrinoid deposition (extending from maternal to fetal surfaces). Therefore, MPFD cases included in the current study would have been classified as either classic MFI or transmural MPFD, but we did not include cases that would be in the borderline MPFD category, as described by Katzman and Genest¹.

The largest pathological review of MPFD was based upon data collected from the Collaborative Perinatal Project.⁴ Naeye et al. described an association between MPFD and stillbirth as well as fetal growth restriction.⁴ Subsequently, additional case reports and case series have reported this pathologic finding in pregnancies with spontaneous abortion,^{1, 5} spontaneous preterm delivery,^{2, 5} and early-onset fetal growth restriction.² In a case-series reported by Andres et al, among 60 pregnancies with MPFD, the prevalence of fetal death was 40% and among the live-born infants, 40% delivered preterm and 58% had birthweights below 10^th percentile for gestational age.² MPFD is also associated with adverse neurodevelopmental outcome in neonates who survive.^{96, 97} Consistent with previous observations, 9 patients with MPFD in the current study resulted in severe fetal growth restriction, placental abruption or fetal death. Specifically, we observed 4 cases of MPFD that presented with spontaneous rupture of membranes and miscarriage in the second trimester.

Risk factors for MPFD include anti-phospholipid antibody syndrome,^{6, 10, 11, 98} elevated maternal serum alpha-feto-protein,⁹⁹ activated protein C resistance,¹⁰⁰ and long-chain-3 hydroxyacyl-CoA Dehydrogenase deficiency.¹⁰¹ The composition of the deposited material has been evaluated and includes fibrin, extracellular matrix proteins (such as fibronectin, laminin, or collagen) and other proteins which are part of the coagulation system.^102-104 MPFD, however, is unlikely the result of a true infarction such as would occur in thrombosis or ischemic necrosis of the villi.^{1, 4} The villi in MPFD are hypoplastic, sclerotic and avascular.^{4, 99} Occasionally, atherosis in the decidual arteries, foci of decidual necrosis and histologic evidence of low uteroplacental blood flow such as small villi and increased syncytial knots similar to those in patients with preeclampsia can be observed.⁴ Placenta from patients with preeclampsia occasionally shows increased fibrinoid material deposition along the basal plate and in the intervillous space.¹⁰⁵ However, the degree of fibrinoid material deposition (as judged by the percentage of villi covered by this material) in the placenta of preeclampsia is generally less than that observed in MPFD cases and does not meet the criteria to diagnose MPFD.¹⁰⁶ It is noteworthy that fibrinoid material deposition has been demonstrated within the glomeruli of patients with preeclampsia.^106-109 Some investigators propose that a prolonged state of slow intravascular coagulation resulting from placental release of unknown factors causes glomerular damage and specific glomerular lesion in preeclampsia.¹¹⁰ The mechanisms leading to adverse pregnancy outcomes in MPFD are unknown. However, it has been proposed that fibrin and/or fibrinoid material deposition interferes with perfusion of the intervillous space and gas/nutrient exchange in the intervillous space resulting in “chronic placental insufficiency”.^{6, 12, 99}

Angiogenic Profile of MPFD Compared to Other Pregnancy Complications

In MPFD, maternal plasma concentrations of sVEGFR-1 were higher across gestational age intervals (marginal difference as a function of time, p=0.09) while that of PlGF was significantly lower than uncomplicated pregnancies after 20 weeks of gestation. The early elevation of sVEGFR-1 in the second trimester especially from 14-16 weeks of gestation without a change in PlGF has never been observed in other pregnancy complications, and appears to be characteristic of MPFD thus far.

Three conclusions could be drawn from these findings. First, an elevation of plasma concentration of sVEGFR-1 is not specific to preeclampsia since none of the patients with MPFD developed new-onset hypertension and proteinuria. Second, although an imbalance of angiogenic/anti-angiogenic factors has been observed in several obstetrical syndromes, the clinical presentation of the disorders may differ depending on the gestational age at which this perturbation occurs. For example, patients destined to develop preterm and term preeclampsia have higher plasma concentrations of sVEGFR-1 starting from 26 and 30 weeks of gestation, respectively, and lower plasma concentrations of PlGF starting from 10-11 weeks of gestation compared with those in uncomplicated pregnancies.²⁹ Different profiles of angiogenic/anti-angiogenic factors have also been reported in pregnancies with spontaneous preterm labor,⁷⁸ small-for-gestational-age neonates^{30, 41} and stillbirth.⁸³ Third, the change in plasma concentrations of angiogenic/anti-angiogenic factors in MPFD was observed prior to the diagnosis of an abnormal pregnancy outcome, and thus, provides an opportunity for the diagnosis and enrollment of these patients for interventional trials especially in patients with a history of MPFD. Sonography may also assist in the prenatal diagnosis of MPFD.⁷

Prevention of Recurrence of MPFD

Several studies suggest that MPFD is a recurrent condition.^{2-4, 7, 10, 13, 99}. Andres et al reported that among 33 pregnancies that occurred after a MPFD, 13 (39%) placentas showed gross and microscopic evidence of MPFD.² Similarly, in many cases included in the current study, patients had prior poor pregnancy outcomes, although placental pathology was not available for review. The strong association between MPFD and serious adverse pregnancy outcomes such as fetal death,^{2, 4-7, 10, 11, 13-16} fetal growth restriction^{1, 2, 4, 6-12} or recurrent miscarriage^{4, 5, 10} strengthens the value of placental pathologic examination in such cases. If MPFD is diagnosed, subsequent pregnancies are also at risk for these complications. The novel identification of abnormal concentrations of angiogenic and anti-angiogenic factors in the current study indicates that an anti-angiogenic state may be a mechanism of disease in MPFD. This has implications because recent observations suggest that there may be therapeutic interventions to reverse an anti-angiogenic state during pregnancy including the administration of pravastatin,^111-114 VEGF 121^115-117 or extracorporeal removal of sVEGFR-1. ¹¹⁸

Strengths and Limitations

This is the first study demonstrating an association between an imbalance of angiogenic/anti-angiogenic factors and MPFD. Moreover, the longitudinal nature of our study allows us to demonstrate that these changes could be detected prior to the diagnosis of MPFD and occurrence of adverse pregnancy outcomes. A limitation of the study was the number of cases, which is a reflection of the low prevalence of the condition. However, the magnitude of the differences in plasma concentrations of angiogenic/anti-angiogenic factors between cases and controls observed herein was remarkable despite this limitation.

Conclusions

An imbalance of angiogenic/anti-angiogenic factors is present in patients with MPFD. We propose that these changes participate in the mechanism of disease responsible for adverse pregnancy outcomes in patients with this placental lesion.