Factor VIII related antigen/coagulant activity ratio as a predictor of fetal growth retardation: a comparison with hormone and uric acid measurements

Biochemical tests of placental function versus ultrasound assessment of fetal size for stillbirth and small-for-gestational-age infants

BACKGROUND

Stillbirth affects 2.6 million pregnancies worldwide each year. Whilst the majority of cases occur in low- and middle-income countries, stillbirth remains an important clinical issue for high-income countries (HICs) - with both the UK and the USA reporting rates above the mean for HICs. In HICs, the most frequently reported association with stillbirth is placental dysfunction. Placental dysfunction may be evident clinically as fetal growth restriction (FGR) and small-for-dates infants. It can be caused by placental abruption or hypertensive disorders of pregnancy and many other disorders and factorsPlacental abnormalities are noted in 11% to 65% of stillbirths. Identification of FGA is difficult in utero. Small-for-gestational age (SGA), as assessed after birth, is the most commonly used surrogate measure for this outcome. The degree of SGA is associated with the likelihood of FGR; 30% of infants with a birthweight < 10th centile are thought to be FGR, while 70% of infants with a birthweight < 3rd centile are thought to be FGR. Critically, SGA is the most significant antenatal risk factor for a stillborn infant. Correct identification of SGA infants is associated with a reduction in the perinatal mortality rate. However, currently used tests, such as measurement of symphysis-fundal height, have a low reported sensitivity and specificity for the identification of SGA infants.

OBJECTIVES

The primary objective was to assess and compare the diagnostic accuracy of ultrasound assessment of fetal growth by estimated fetal weight (EFW) and placental biomarkers alone and in any combination used after 24 weeks of pregnancy in the identification of placental dysfunction as evidenced by either stillbirth, or birth of a SGA infant. Secondary objectives were to investigate the effect of clinical and methodological factors on test performance.

SEARCH METHODS

We developed full search strategies with no language or date restrictions. The following sources were searched: MEDLINE, MEDLINE In Process and Embase via Ovid, Cochrane (Wiley) CENTRAL, Science Citation Index (Web of Science), CINAHL (EBSCO) with search strategies adapted for each database as required; ISRCTN Registry, UK Clinical Trials Gateway, WHO International Clinical Trials Portal and ClinicalTrials.gov for ongoing studies; specialist abstract and conference proceeding resources (British Library's ZETOC and Web of Science Conference Proceedings Citation Index). Search last conducted in Ocober 2016.

SELECTION CRITERIA

We included studies of pregnant women of any age with a gestation of at least 24 weeks if relevant outcomes of pregnancy (live birth/stillbirth; SGA infant) were assessed. Studies were included irrespective of whether pregnant women were deemed to be low or high risk for complications or were of mixed populations (low and high risk). Pregnancies complicated by fetal abnormalities and multi-fetal pregnancies were excluded as they have a higher risk of stillbirth from non-placental causes. With regard to biochemical tests, we included assays performed using any technique and at any threshold used to determine test positivity.

DATA COLLECTION AND ANALYSIS

We extracted the numbers of true positive, false positive, false negative, and true negative test results from each study. We assessed risk of bias and applicability using the QUADAS-2 tool. Meta-analyses were performed using the hierarchical summary ROC model to estimate and compare test accuracy.

MAIN RESULTS

We included 91 studies that evaluated seven tests - blood tests for human placental lactogen (hPL), oestriol, placental growth factor (PlGF) and uric acid, ultrasound EFW and placental grading and urinary oestriol - in a total of 175,426 pregnant women, in which 15,471 pregnancies ended in the birth of a small baby and 740 pregnancies which ended in stillbirth. The quality of included studies was variable with most domains at low risk of bias although 59% of studies were deemed to be of unclear risk of bias for the reference standard domain. Fifty-three per cent of studies were of high concern for applicability due to inclusion of only high- or low-risk women.Using all available data for SGA (86 studies; 159,490 pregnancies involving 15,471 SGA infants), there was evidence of a difference in accuracy (P < 0.0001) between the seven tests for detecting pregnancies that are SGA at birth. Ultrasound EFW was the most accurate test for detecting SGA at birth with a diagnostic odds ratio (DOR) of 21.3 (95% CI 13.1 to 34.6); hPL was the most accurate biochemical test with a DOR of 4.78 (95% CI 3.21 to 7.13). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.88 and median prevalence of 19%, EFW, hPL, oestriol, urinary oestriol, uric acid, PlGF and placental grading will miss 50 (95% CI 32 to 68), 116 (97 to 133), 124 (108 to 137), 127 (95 to 152), 139 (118 to 154), 144 (118 to 161), and 144 (122 to 161) SGA infants, respectively. For the detection of pregnancies ending in stillbirth (21 studies; 100,687 pregnancies involving 740 stillbirths), in an indirect comparison of the four biochemical tests, PlGF was the most accurate test with a DOR of 49.2 (95% CI 12.7 to 191). In a hypothetical cohort of 1000 pregnant women, at the median specificity of 0.78 and median prevalence of 1.7%, PlGF, hPL, urinary oestriol and uric acid will miss 2 (95% CI 0 to 4), 4 (2 to 8), 6 (6 to 7) and 8 (3 to 13) stillbirths, respectively. No studies assessed the accuracy of ultrasound EFW for detection of pregnancy ending in stillbirth.

AUTHORS' CONCLUSIONS

Biochemical markers of placental dysfunction used alone have insufficient accuracy to identify pregnancies ending in SGA or stillbirth. Studies combining U and placental biomarkers are needed to determine whether this approach improves diagnostic accuracy over the use of ultrasound estimation of fetal size or biochemical markers of placental dysfunction used alone. Many of the studies included in this review were carried out between 1974 and 2016. Studies of placental substances were mostly carried out before 1991 and after 2013; earlier studies may not reflect developments in test technology.

Reassessment of von Willebrand factor (VWF), VWF propeptide, factor VIII:C and plasminogen activator inhibitors 1 and 2 during normal pregnancy

The use of von Willebrand factor [VWF antigen (WF:Ag)] measurement as a marker of endothelial cell activation for monitoring hypertensive pregnancies is limited by the poor definition of reference values. We reassessed these reference values using different assays, and those of the propeptide (VWF:Ag II) and factor VIII coagulant activity (factor VIII:C), in a large population of normal pregnancies, at 3-week intervals of gestational age. Plasminogen activator inhibitors (PAI-1 and PAI-2) were measured in parallel. Blood was collected at single time points between 12 weeks and delivery in 306 women undergoing normal singleton pregnancy. For clinical purposes, the VWF:Ag reference values were assay independent and the influence of ABO blood group on VWF:Ag or factor VIII:c was found to be limited during the third trimester. VWF:Ag II was not influenced by the ABO blood group. The ratio, VWF:Ag/factor VIII:C was close to 1.0 throughout pregnancy. In contrast, VWF:Ag II increased more slowly than VWF:Ag and the ratio of VWF:Ag II to VWF:Ag in plasma decreased from 1.00 to 0.5 at term. PAI-1 and PAI-2 increased with gestational age, but PAI-2 decreased during the last 2 weeks, indicating physiological placental regression at the very end of pregnancy.

Evidence of in vivo generation of thrombin in patients with small-for-gestational-age fetuses and pre-eclampsia

OBJECTIVE

Thrombotic lesions in the maternal or fetal compartments are frequently observed in the placentas of patients with small-for-gestational-age (SGA) fetuses and in pre-eclampsia. The objective of this study was to determine whether there was evidence of in vivo generation of thrombin, the rate-limiting enzyme responsible for the formation of fibrin. The plasma concentrations of thrombin-antithrombin (TAT) complexes were used as an index of thrombin generation.

METHODS

TAT complexes were measured in the plasma from 68 women from the following groups: normal pregnancy (n = 29); pre-eclampsia (n = 26); and SGA (defined as estimated fetal weight below the 10th centile for gestational age, which was confirmed by neonatal birth weight) (n = 13). TAT complex plasma concentrations were determined with a specific and sensitive immunoassay. Statistical analysis was performed with non-parametric statistics.

RESULTS

The median plasma TAT complex concentrations were significantly higher in patients who delivered SGA neonates than in normal pregnant women (SGA, median 24.2 microg/l; range 11.9-788.7 vs. normal pregnancy, median: 14.4 microg/l; range 6.8-26.9; p = 0.001). Patients with pre-eclampsia had a higher median plasma TAT complex concentration than normal pregnant women (pre-eclampsia, median 18.1 microg/l; range 10.0-75.2 vs. normal pregnancy, median 14.4 microg/l; range 6.8-26.9; p = 0.02).

CONCLUSION

In vivo generation of thrombin, determined by the plasma concentrations of TAT complexes, is higher in patients with SGA fetuses and patients with pre-eclampsia than in normal pregnancy.

Maternal endothelial soluble cell adhesion molecules with isolated small for gestational age fetuses: comparison with pre-eclampsia

OBJECTIVE

1. To evaluate the activation profile of the endothelium in pregnancies complicated by small for gestational age fetuses compared with pre-eclampsia and normal pregnancy, by measuring the plasma levels of soluble adhesion molecules soluble E-selectin, intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1. 2. To determine whether soluble adhesion molecules were related to the severity of small for gestational age fetuses and pre-eclampsia.

DESIGN

Observational study.

PARTICIPANTS

Sixteen women with small for gestational age fetuses; 15 women with pre-eclampsia and 15 healthy primigravidae were recruited as controls.

METHODS

Plasma levels of soluble E-selectin, intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 were measured by ELISA.

RESULTS

Compared with the healthy controls, soluble E-selectin was significantly increased in both small for gestational age fetuses and pre-eclampsia, whereas intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 were increased only in pre-eclampsia. In the small for gestational age fetuses group, soluble E-selectin correlated inversely with the ratio between birthweight and the expected normal birthweight (r = -0.4, P = 0.007). In the pre-eclampsia group, a significant correlation was observed between vascular cell adhesion molecule-1 and blood pressure (r = 0.54, P = 0.039).

CONCLUSIONS

Endothelial activation, reflected by raised levels of soluble E-selectin, is a feature of small for gestational age fetuses and is correlated with the severity of the disease. Differences in the profile of soluble cell adhesion molecules suggest variations in the degrees of endothelial activation between pre-eclampsia and small for gestational age fetuses.

Lone hyperuricemia during pregnancy: maternal and fetal outcomes

OBJECTIVE

Study of maternal and fetal consequences of lone hyperuricemia during pregnancy and demonstration that lone hyperuricemia is not a risk factor regarding the onset of preeclampsia.

STUDY DESIGN

Retrospective study of two groups of women, one found to have lone hyperuricemia during pregnancy (n=102) and the others with normal serum uric acid levels (n=100).

RESULTS

The only consequence identified of the lone hyperuricemia was a lower birth weight of children born to mothers found to have lone hyperuricemia for more than 2 weeks (P<0.05).

CONCLUSIONS

Lone hyperuricemia is not a risk factor regarding the onset of preeclampsia. It is therefore unnecessary to measure serum uric acid level during a normal pregnancy.

Plasma cellular fibronectin as a measure of endothelial involvement in preeclampsia and intrauterine growth retardation

OBJECTIVE

Our purpose was to determine the presence and degree of endothelial injury, by measuring plasma concentrations of cellular fibronectin, in pregnancies complicated by preeclampsia or intrauterine growth retardation.

STUDY DESIGN

A matched, nested, case-control study design was used. Plasma was collected prospectively from pregnant women throughout gestation. At least 12 weeks after delivery women with preeclampsia, both preeclampsia and intrauterine growth retardation, or intrauterine growth retardation alone were identified. Normal controls were matched to these patients by age, race, and gestational age. Stored plasma, which had been obtained in the third trimester, was assayed for cellular fibronectin by means of a sensitive and specific enzyme immunoassay. After an appropriate transformation of the data results were compared with one-way analysis of variance with Fisher's post hoc test.

RESULTS

Patients with preeclampsia (n = 18) had higher plasma cellular fibronectin concentrations than did control patients (n = 68) with median values of 2.8 and 1.4 micrograms/ml, respectively (p < 0.001, using transformed data). Patients with intrauterine growth retardation alone (n = 10) had 2.3 micrograms/ml cellular fibronectin, significantly higher than values of controls (p < 0.02 using transformed data) and significantly lower than those of patients with preeclampsia (p < 0.05 using transformed data).

CONCLUSION

Pregnancies complicated by preeclampsia had significantly higher plasma cellular fibronectin concentrations than did pregnancies with intrauterine growth retardation alone, which in turn had significantly higher plasma cellular fibronectin concentrations than did control pregnancies. We speculate that endothelial involvement in intrauterine growth retardation is confined to the uteroplacental circulation, whereas it is systemic in preeclampsia.

Early detection of preeclampsia

The signs and symptoms of preeclampsia are usually apparent at a relatively late stage in pregnancy (late second to early third trimester). However, the disorder results from abnormal interaction between fetal and maternal tissue much earlier in pregnancy, between 8 and 18 weeks' gestation. During the past two decades numerous clinical, biophysical, and biochemical tests have been proposed for the early detection of preeclampsia. Some of these tests are simple, whereas others are invasive; some have been studied extensively, while others are still under clinical investigation. A review of the literature indicates considerable disagreement regarding the sensitivity and predictive values of the various tests studied. The reported differences in the predictive values of these tests may be attributed to one or more of the following: populations studied, definition and prevalence of the disorder, techniques and methodology used in performing these tests, etc. As a result, there is disagreement regarding the ideal screening test to be used for identifying patients for clinical trials dealing with prevention of the disorder.

The factor VIII ratio in normal and pathological pregnancies

The factor VIII ratio was measured in 102 pregnant women (43 uncomplicated pregnancies, 19 with pre-eclampsia without fetal growth retardation, 8 pre-eclampsia complicated by fetal growth retardation, 12 with only fetal growth retardation and 20 with gestational diabetes). The pathological pregnancies showed a statistically significant elevation of the factor VIII ratio compared to the normal pregnancies. The group of pre-eclampsia complicated by fetal growth retardation showed the most marked increase of the factor VIII ratio. The results are discussed in relation to the hypothesis that the elevated factor VIII ratio is mainly due to the release of factor VIII antigen by various forms of vascular stress.

Antithrombin III in normal pregnancy

Plasma antithrombin III (AT III) was determined in 94 women during and after normal pregnancy employing an automated amidolytic technique. The patients were selected on the following criteria: no toxaemia, spontaneous delivery at term, birth-weight above the 10th percentile and discharged with a healthy baby. AT III levels during pregnancy and early puerperium were not lower than own control values obtained 6-8 weeks after delivery.

Plasma antithrombin III activity: an aid in the diagnosis of preeclampsia-eclampsia

Plasma antithrombin III (AT III) activity was examined retrospectively in patients with preeclampsia-eclampsia, chronic hypertension, and chronic hypertension with superimposed preeclampsia-eclampsia. Levels of AT III were greater than 1 SD below normal pregnant control in each case of preeclampsia-eclampsia syndrome. The degree of reduction in plasma AT III activity was correlated with the severity of disease. AT III activity was within normal limits in patients with chronic hypertension. AT III activity dropped prior to the appearance of clinically evident disease in three patients who were followed from an early gestational age. In no instance was low plasma AT III activity associated with normal pregnancy. Coincidental disease, including pyelonephritis and a viral syndrome, were associated with markedly decreased levels of plasma AT III activity in otherwise normal pregnancies. Plasma AT III activity may be valuable as a tool in diagnosing preeclampsia-eclampsia, as a screening test for preclinical preeclampsia-eclampsia, and as an indicator of severity of disease.