Shared and disparate components of the pathophysiologies of fetal growth restriction and preeclampsia

Preeclampsia--a pressing problem: an executive summary of a National Institute of Child Health and Human Development workshop

On September 21 and 22, 2006, the National Institute of Child Health and Human Development of the National Institutes of Health sponsored a 2-day workshop titled "Preeclampsia--A Pressing Problem." The purpose of the workshop was to bring together leaders in the field to present and discuss their diverse research areas, which ranged from basic science to clinical trials and management, and to identify scientific gaps. This article is a summary of the proceedings of that workshop. Although much progress is being made in understanding the underpinnings of preeclampsia, a number of research gaps are identified that, if filled, would hasten progress in the field. It is the overall consensus that preeclampsia is a multifactorial disease whose pathogenesis is not solely vascular, genetic, immunologic, or environmental but a complex combination of factors. In addition, a number of specific scientific gaps are identified including insufficient multidisciplinary and collaborative research, clinical trials and studies of patient management, and a lack of in-depth mechanistic research. The research community needs to focus on these gaps to better understand the disease, with the ultimate goal of preventing the disorder.

Prepregnancy cardiovascular risk factors as predictors of pre-eclampsia: population based cohort study

OBJECTIVE

To examine the effect of cardiovascular risk factors before pregnancy on risk of pre-eclampsia.

DESIGN

Population based prospective study.

SETTING

Linkage between a Norwegian population based study (Nord-Trøndelag health study, HUNT-2) and Norway's medical birth registry.

PARTICIPANTS

3494 women who gave birth after participating in the Nord-Trøndelag health study at baseline; of whom 133 (3.8%) delivered after a pre-eclamptic pregnancy.

MAIN OUTCOME MEASURE

Odds ratio of developing pre-eclampsia.

RESULTS

After adjustment for smoking; previous pre-eclampsia; parity; maternal age, education, and socioeconomic position; and duration between baseline measurements and delivery, positive associations were found between prepregnancy serum levels of triglycerides, cholesterol, low density lipoprotein cholesterol, non-high density lipoprotein cholesterol, and blood pressure and risk of pre-eclampsia. The odds ratio of developing pre-eclampsia for women with baseline systolic blood pressures greater than 130 mm Hg (highest fifth) was 7.3 (95% confidence interval 3.1 to 17.2) compared with women with systolic blood pressures less than 111 mm Hg (lowest fifth). Similar results were found for nulliparous and parous women. Women who used oral contraceptives at baseline had half the risk of pre-eclampsia compared with never or former users (0.5, 0.3 to 0.9).

CONCLUSION

Women with cardiovascular risk factors may be predisposed to pre-eclampsia.

Diabetes mellitus in the 21 years after a pregnancy that was complicated by hypertension: findings from a prospective cohort study

OBJECTIVE

The purpose of this study was to examine the relationship between hypertensive disorders of pregnancy (HDP) and self-reported diabetes mellitus 21 years after delivery.

STUDY DESIGN

The Mater-University of Queensland Study is a prospective cohort study of women who received antenatal care at a major public hospital in Brisbane, Australia, between 1981 and 1984; 3639 women who completed the questionnaire at 21 years postpartum were included.

RESULTS

Of the women without HDP, 7.4% reported a diagnosis of diabetes mellitus compared with 15.3% of the women with HDP (unadjusted odds ratio [OR], 2.03; 95% CI, 1.42, 2.91). After adjustment for all potentially explanatory variables, only prepregnancy body mass index (BMI) and BMI at 21 years after delivery resulted in attenuation of the association (fully adjusted OR, 1.76; 95% CI, 1.21, 2.56). In a smaller subgroup, waist circumference and BMI at 21 years had similar effects on point estimates (fully adjusted OR with BMI, 1.64 [95% CI, 1.11, 2.42]; fully adjusted OR with waist, 1.60 [95% CI, 1.08, 2.40]).

CONCLUSION

HDP are associated with reported diagnosis of diabetes mellitus 21 years after delivery.

The effect of low body mass index on the development of gestational hypertension and preeclampsia

OBJECTIVES

To evaluate the relationship between low maternal body mass index (BMI) as calculated in the first trimester and the risk of preeclampsia and gestational hypertension.

METHODS

Patients enrolled in the First And Second Trimester Evaluation of Risk for aneuploidy (FASTER) trial were grouped into three weight categories: low BMI (BMI <19.8 kg/m2), normal BMI (BMI 19.8 - 26 kg/m2), and overweight BMI (26.1 - 29 kg/m2). The incidences of gestational hypertension and preeclampsia were ascertained for each group. Tests for differences in crude incidence proportions were performed using Chi-square tests. Multiple logistic regression was used to adjust for maternal age, race, parity, obesity, use of assisted reproductive technology (ART), in vitro fertilization (IVF), gestational diabetes, pre-gestational diabetes, cocaine use, and smoking.

RESULTS

The proportion of patients having gestational hypertension in the low BMI group was 2.0% compared to 3.2% for normal BMI and 6.0% for overweight BMI (p < 0.0001). Women with low BMI were also less likely to develop preeclampsia, 1.1% vs. 1.9% for normal BMI and 2.8% for overweight BMI (p < 0.0001).

CONCLUSIONS

We found that women with low BMI in the first trimester were significantly less likely to develop gestational hypertension or preeclampsia than women with a normal BMI.

Placental angiogenesis markers sFlt-1 and PlGF: response to cigarette smoke

OBJECTIVE

Excess soluble vascular endothelial growth factor receptor, fms-like tyrosine kinase-1 (sFlt-1), and reduced placental growth factor (PlGF) mediate the genesis of preeclampsia. Cigarette smoking reduces the risk of preeclampsia. We hypothesized that placental secretion of sFlt-1 and PlGF was affected by exposure to cigarette smoke extract.

STUDY DESIGN

Term placental villous explants were cultured with cigarette smoke extract. Media were analyzed for sFlt-1 and PlGF. Apoptosis was measured by TUNEL staining. Results are reported as sFlt-1 or PlGF picogram/milliliter/milligram wet weight of explant.

RESULTS

Exposure to cigarette smoke extract reduced secretion of sFlt-1 in a dose-dependent manner. There was no difference in apoptosis. In contrast with sFlt-1, PlGF did not decline when incubated with cigarette smoke extract.

CONCLUSION

Exposure of placental villous explants to cigarette smoke extract results in a proangiogenic state with reduced sFlt-1 and relative abundance of PlGF. This is the reverse of changes that are seen in preeclampsia and may explain the reduction of preeclampsia in smokers.

Regulation of Placental Nutrient Transport – A Review

Fetal growth is primarily determined by nutrient availability, which is intimately related to placental nutrient transport. Detailed information on the regulation of placental nutrient transporters is therefore critical in order to understand the mechanisms underlying altered fetal growth and fetal programming. After briefly summarizing the cellular mechanisms for placental transport of glucose, amino acids and free fatty acids, we will discuss factors shown to regulate placental nutrient transporters and review the data describing how these factors are altered in pregnancy complications associated with abnormal fetal growth. We propose an integrated model of regulation of placental nutrient transport by maternal and placental factors in IUGR.

Implantation and early embryonic development: implications for pregnancy

Implantation represents the limiting step in governing reproductive outcomes. The process is driven by both embryo and endometrium alike. Minute perturbations in this orchestration lay foundation for pregnancy-associated complications that may manifest throughout the gestational course. Furthermore, placental function dictates many aspects of fetal development inclusive of preeclampsia and intrauterine growth restriction (IUGR). Novel techniques such as Multigate Spectral Doppler Analysis (MSDA) may allow for early detection and diagnosis of potentially deleterious fetal outcomes.

STOX1 gene in pre-eclampsia and intrauterine growth restriction

The STOX1 gene, identified as a candidate gene for pre-eclampsia in Dutch women, is placentally expressed and subject to imprinting with preferential transmission of the maternal allele. In our study, STOX1-Y153H frequencies were similar in 157 women with pre-eclampsia (65%) and in 157 controls (64%) from the general Dutch population. In an isolated Dutch population, a distortion could not be demonstrated in the transmission of STOX1-Y153H variation from heterozygous mothers to offspring in 50 and 56 families with pregnancies complicated by pre-eclampsia or intrauterine growth restriction, respectively. Our findings do not confirm previous suggestions that STOX1 plays a major role in Dutch women with pre-eclampsia.

Recurrence of Ischemic Placental Disease

OBJECTIVE

To test the hypothesis that the presence of preeclampsia, small for gestational age (SGA)-birth, and placental abruption in the first pregnancy confers increased risk in the second pregnancy.

METHODS

A retrospective cohort study entailing a case-crossover analysis was performed based on women who had two consecutive singleton live births (n=154,810) between 1989 and 1997 in Missouri. Small for gestational age was defined as infants with birth weight below the 10th centile for gestational age. Risk and recurrence of ischemic placental disease was assessed from fitting logistic regression models after adjusting for several confounders.

RESULTS

Preeclampsia in the first pregnancy was associated with significantly increased risk of preeclampsia (odds ratio 7.03, 95% confidence interval 6.51, 7.59), SGA (odds ratio 1.16, 95% confidence interval 1.06, 1.27), and placental abruption (odds ratio 1.90, 95% confidence interval 1.51, 2.38) in the second pregnancy. Similarly, women with SGA and abruption in the first pregnancy were associated with increased risks of all other conditions in the second pregnancy.

CONCLUSION

Women with preeclampsia, SGA, and placental abruption in their first pregnancy--conditions that constitute ischemic placental disease--are at substantially increased risk of recurrence of any or all these conditions in their second pregnancy. Although causes of these conditions remain largely speculative, these entities may manifest through a common pathway of ischemic placental disease with significant risk of recurrence.

Fetal growth restriction and subsequent pregnancy risks

Fetal growth restriction can result from a variety of intrinsic or extrinsic insults, resulting from maternal, fetal, and placental factors. Determining the underlying cause of poor fetal growth can be difficult but is essential for assessing potential risks for future pregnancies. Importantly, recurrence risks greatly depend on these underlying conditions. Understanding these risks can allow more appropriate patient counseling and may influence management strategies to optimize future pregnancies.

Placental HIF-1 alpha, HIF-2 alpha, membrane and soluble VEGF receptor-1 proteins are not increased in normotensive pregnancies complicated by late-onset intrauterine growth restriction

Inadequate trophoblast invasion and spiral artery remodeling leading to poor placental perfusion are believed to underlie the pregnancy pathologies preeclampsia (PE) and intrauterine growth restriction (IUGR). The main objective of this study was to investigate hypoxia-inducible transcription factor-alpha (HIF-alpha) and downstream genes (VEGF receptor-1) Flt-1 and soluble fms-like tyrosine kinase 1 (sFlt-1) proteins in IUGR placentas. Placentas from normal pregnant (NP; n = 18), PE (n = 18), and IUGR (n = 10) patients were investigated. Normotensive patients with IUGR delivered babies at >or= 37 wk of gestation with birth weights of <10% and asymmetrical growth. HIF-1 alpha, -2 alpha, Flt-1, and sFlt-1 protein, and mRNA were assessed by Western and Northern blot analyses, respectively. The results are expressed as ratios of the densitometric values for each pair of pathologic and normal placentas, a ratio of 1.0 indicating no difference. Comparable to our earlier studies, the PE/NP ratios for HIF-1 alpha, -2 alpha, and Flt proteins were significantly increased by 50-100% (all P < 0.01 vs. 1.0). Unexpectedly, the IUGR/NP ratios for HIF-1 alpha and -2 alpha proteins were 1.03 +/- 0.07 and 0.96 +/- 0.16, respectively, and for Flt and sFlt were 1.14 +/- 0.15 and 0.95 +/- 0.12, respectively (all P = not significant vs. 1.0). Northern blot analysis revealed comparable levels of HIF-alpha mRNA in abnormal and normal placentas. In contrast to PE, HIF-alpha proteins and regulated genes are not increased in placentas from normotensive pregnant women delivering small, asymmetrically grown babies >or= 37 wk of gestation. The absence of an increase in HIF-alpha protein is not due to insufficient HIF-alpha mRNA for protein synthesis. Thus, the placentas from women with PE and late IUGR are fundamentally different at the molecular level.

In utero imaging of the placenta: importance for diseases of pregnancy

Maurice Panigel demonstrated by X-rays, almost 40 years ago, placental maternal blood jets in non-human primates. Although to researchers the importance of the placenta is evident, in clinical obstetrical imaging, the fetus takes precedence. The placenta is imaged almost as an after thought and mostly to determine its location in the uterus. In animal species, the placenta was imaged with techniques which would be considered too invasive (or too costly for routine use) in humans, many pioneered by Panigel: radioangiography, radioisotopes scintigraphy, thermography, magnetic resonance imaging (MRI) and spectroscopy, positive emission tomography (PET) and single photon emission computed tomography (SPECT). Ultrasound allows for detailed, and, as far as is known, safe analyses of not only placental structure in the human but also its function. Earlier, only 2-dimensional grey-scale was available and more than 20 years ago, placental grading was popular. Later, colour imaging and spectral Doppler analysis of blood velocity both in the umbilical artery and within the placenta as well as the uterus and fetal vessels became essential and, more recently, the use of ultrasound contrast agents has been described, albeit not yet in a clinical setting. Three-dimensional ultrasound permits evaluation of the placenta in several planes, more precise depiction of internal vasculature as well as more accurate volume assessment. Several medical disorders of the pregnant woman or her fetus begin or end in the placenta, and ultrasound is the optimal investigation method. Obvious examples include pre-eclampsia and other forms of hypertension in pregnancy, less than optimal fetal growth (i.e. intrauterine growth restriction), triploidy (and its placental manifestation: partial mole), non-immune hydrops as well as several infectious processes. Ultrasound is also particularly suited to evaluate specific placental conditions, such as abnormal placentation (placenta previa and accrete for instance), gestational trophoblastic disease and placental tumors (e.g. chorioangioma).

Young maternal age at delivery is associated with asthma in adult offspring

OBJECTIVE

Some studies have shown an association between lower maternal age at delivery and increased asthma in children and young adults. It is unclear whether this represents an effect of maternal ageing or a protective effect of siblings. In a North-European population based study, we investigated whether mother's age at delivery was associated with risk for asthma and hay fever in adult offspring, taking into account relevant confounders.

METHODS

A total of 16,190 subjects (74%) aged 23-54 yr answered a postal questionnaire in a follow-up of the European Community Respiratory Health Survey (ECRHS I).

RESULTS

The associations of maternal age at delivery with hay fever, respiratory symptoms and diagnosed asthma were analysed using logistic regression, adjusting for household size, dwelling, parental education, centre, gender, adult hay fever, smoking, age and body mass index (BMI). The adjusted odds ratios (95% CI) for wheeze with breathlessness, wheeze without a cold and asthma in the offspring were 0.94 (0.90-0.99), 0.89 (0.86-0.94) and 0.92 (0.88-0.97), respectively, per 5 yr increase in maternal age. No heterogeneity between centres was found (p=0.84). The estimates remained similar in sub-sample analyses when adjusting for siblings, maternal smoking (n=3109) and for birth weight (n=1686). Hay fever was more common among those with the youngest and oldest mothers.

CONCLUSIONS

In this large North-European multi-centre study, asthma was less common with increasing maternal age. This effect was consistent between centres and persisted with adjustment for several potential confounders, suggesting that the association may possibly be explained by biological changes related to maternal ageing.

Distinct subsets of microRNAs are expressed differentially in the human placentas of patients with preeclampsia

OBJECTIVE

Preeclampsia and small-for-gestational age (SGA) neonates have partially overlapping clinicopathologic features. MicroRNAs (miRNAs) are critical posttranscriptional regulators of gene expression. This study was performed to determine whether preeclampsia and SGA are associated with alterations in placental miRNA expression.

STUDY DESIGN

Placentas were obtained from patients with (1) preeclampsia (n = 9); (2) SGA (n = 9); (3) preeclampsia + SGA (n = 9); and (4) a control group with spontaneous preterm labor and delivery (PTL; n = 9). The expression of 157 miRNAs was assessed by real-time quantitative reverse transcription-polymerase chain reaction.

RESULTS

Differential expression between preeclampsia and the control group (miR-210, miR-182) and between preeclampsia + SGA and the control group (miR-210, miR-182*, and others) was found. Gene Ontology analysis of the target genes revealed enrichment for specific biological process categories (antiapoptosis: miR-182; regulation of transcription: miR-210).

CONCLUSION

This study reports, for the first time, increased expression of specific placental miRNAs in preeclampsia with and without SGA. The findings also provide novel targets for further investigation of the pathophysiology of preeclampsia.

Expressional and epigenetic alterations of placental serine protease inhibitors: SERPINA3 is a potential marker of preeclampsia

Preeclampsia is the major pregnancy-induced hypertensive disorder. It modifies the expression profile of placental genes, including several serine protease inhibitors (SERPINs). The objective of this study was to perform a systematic expression analysis of these genes in normal and pathological placentas and to pinpoint epigenetic alterations inside their promoter regions. Expression of 18 placental SERPINs was analyzed by quantitative RT-PCR on placentas from pregnancies complicated by preeclampsia, intrauterine growth restriction, or both and was compared with normal controls. SERPINA3, A5, A8, B2, B5, and B7 presented significant differences in expression in >or=1 pathological situation. In parallel, the methylation status of the CpG islands located in their promoter regions was studied on a sample of control and preeclamptic placentas. Ten SERPIN promoters were either totally methylated or totally unmethylated, whereas SERPINA3, A5, and A8 presented complex methylation profiles. For SERPINA3, the analysis was extended to 81 samples and performed by pyrosequencing. For the SERPINA3 CpG island, the average methylation level was significantly diminished in preeclampsia and growth restriction. The hypomethylated CpGs were situated at putative binding sites for developmental and stress response (hypoxia and inflammation) factors. Our results provide one of the first observations of a specific epigenetic alteration in human placental diseases and provide new potential markers for an early diagnosis.