It is now well established that maternal serum markers are often abnormal in fetal trisomy 21. Their determination is recommended for prenatal screening and pregnancy follow-up. However, mechanisms leading to abnormal maternal serum levels of such markers are still debated. Our objective was to help clinicians and scientists unravel the pathophysiology of these markers via a review of the main studies published in this field, both in vivo and in vitro, focusing on the six most widely used markers (hCG, its free subunit hCGβ, PAPP-A, AFP, uE3, and inhibin A) as well as cell-free feto-placental DNA. Analysis of the literature shows that mechanisms underlying each marker's regulation are multiple and not necessarily directly linked with the supernumerary chromosome 21. The crucial involvement of the placenta is also highlighted, which could be defective in one or several of its functions (turnover and apoptosis, endocrine production, and feto-maternal exchanges and transfer). These defects were neither constant nor specific for trisomy 21, and might be more or less pronounced, reflecting a high variability in placental immaturity and alteration. This explains why maternal serum markers can lack both specificity and sensitivity, and are thus restricted to screening.
Ultrasound scanning is useful to detect neural tube defect (NTD) but scarcely distinguished between closed NTD and open NTD, which had very different prognosis. An amniotic fluid punction is thus mandatory to search for an increase in alpha foeto protein (AFP) levels and for the presence of acetylcholinesterase which identified open NTD. However, AFP levels fluctuate both with the gestational age and the assay used. Our aim was to establish normative values for AFP in amniotic fluid in the second half of pregnancy using three different immunoassays and to improve their clinical relevance. Amniotic fluid punctions were performed on 527 patients from 9 week of gestation (WG) to 37 WG either for maternal age, Trisomy 21 screening, increase in nucal translucency (control group, n = 527) or for suspicion of neural tube defect or abdominal defect (n = 5). AFP was measured using the immunoassay developed for serum AFP on the Access 2 system, the Immulite 2000 and the Advia Centaur. Results were expressed in ng/ml, multiple of the median (MoM) and percentiles. AFP decrease by 1.5 fold between 9 and 19 WG. When NTD was suspected, an increase in anmniotic AFP was observed (from 2.5 MoM to 9.3 MoM) confirming an open NTD. In conclusion, the assay developed on those 3 automates is suitable for the measurement of AFP in amniotic fluid.
The proinsulin molecule results from the cleavage of pre-pro-insulin, produced in pancreatic beta cells. Its subsequent -cleavage allows the release of insulin, the key hormone of glycemia regulation and C-peptide in equimolar proportions. During fasting trial, insulinoma diagnosis relies on inadequately high insulin and C-peptide serum levels concomitant with an hypoglycemia. In this context, proinsulin assay can be interesting in the cases of discrepancy between the two parameters. In diabetes, endoplasmic reticulum stress and beta cells inflammation, lead to the secretion of misfolded proinsulin molecules. Thus, in type 2 diabetes, proinsulin/insulin ratio increases with the degree of insulin resistance. In type 1 diabetes, proinsulin/C-peptide ratio could predict the onset of diabetes in relatives. In our practice, serum pro-insulin determined using an Elisa immunoassay (Millipore®) during fasting trial can be complementary to C-peptide and insulin assays in relation to glycemia to label an hypoglycemia. In case of glucose intolerance and diabetes, proinsulin could thus be measured.
The placental growth factor (PlGF) and its soluble receptor (sFlt-1) are circulating angiogenic factors. During pregnancy these factors are released by the placenta into the maternal circulation. Preeclampsia affects 2-7% of pregnant women according to their risk factors and is characterized by high blood pressure and the onset of de novo proteinuria in the second half of pregnancy. Alterations of the sFlt-1/PlGF ratio in preeclampsia correlate with the diagnosis and adverse outcomes, particularly when the disease presents prematurely (<34 weeks). These factors can be assayed in maternal blood and measuring the sFlt-1/PlGF ratio is now available. We propose in this work to update the knowledge of these two molecules, describe their roles and evolution during normal pregnancy and preeclampsia, and finally to focus on the available assays.
Diagnosis of endogenous hyperinsulinism relies on the occurrence of a hypoglycemia, concomitant with inadequate high insulin and C-peptide levels. However, diagnostic cutoffs are not consensual among the different learned societies. The objective of this work was to propose optimized cutoffs for these three parameters for the diagnosis of endogenous hyperinsulinism.All the patients having performed a fasting trial in Cochin Hospital Endocrinology Department between February 2012 and August 2022 were included. The results of glycemia, insulin and C-peptide levels during fasting trial were collected and analyzed.One hundred and fifty-nine patients were included: 26 with endogenous hyperinsulinism and 133 without endogenous hyperinsulinism. ROC analysis of glycemia nadir during fasting trial identified the value of 2.3 mmol/L as the optimal cutoff, ensuring a sensitivity of 100% associated with a specificity of 81%. ROC analysis of insulin and C-peptide levels concomitant with hypoglycemia <2.3 mmol/L showed very good diagnostic performances of both parameters with respective cutoffs of 3.1 mUI/L (=21.5 pmol/L; sensitivity = 96%; specificity = 92%) and 0.30 nmol/L (sensitivity = 96%; specificity = 100%). Insulin to glycemia ratio as well as C-peptide to glycemia ratio (in pmol/mmol) at the time of glycemia nadir did not show better diagnostic performances than C-peptide alone.A C-peptide level 0.3 nmol/L concomitant with a hypoglycemia <2.3 mmol/L appears as the best criterion to make the diagnosis of endogenous hyperinsulinism. Insulin level can be underestimated on hemolyzed blood samples, frequently observed in fasting trial, and thus shows lower diagnostic performances.
Preeclampsia is a syndrome specific of pregnancy and placenta diagnosed after 20 WG on the association of an hypertension and a proteinuria. It is responsible for significant maternal-fetal morbidity and mortality which justify the development of markers for screening, diagnosis and prognosis. These markers are actors or witnesses to the various stages and mechanisms of the disease : the initial defect of trophoblast invasion and remodeling of uterine arteries (proteases [PAPP-A, ADAM-12, uPA, MMPs], their inhibitors, and angiogenic factors [PlGF, sflt-1, s-eng]) which induces hydrostatic abnormalities (uterine doppler) and placental hypoperfusion with dysoxia (HIF-1α) and oxidative stress (free radicals, peroxynitrites, oxidized LDL). This results in impaired placental functions including endocrine and metabolic functions (hCG, leptin) with increase in placental apoptosis and necrosis with the release of exosomes and toxic placental fragments (STBM) and their content (RNA, DNA and proteins). This fragments amplify the gestational inflammation (IL6, TNFα ; activation of leukocytes and macrophages [elastase, neopterin] and complement) and lead to a deterioration of the maternal endothelium (vasoconstriction [ET2, TxA2]; platelet adhesion [sVCAM -1α), aggregation and activation; impaired vascular permeability) generating edema, hypertension, atherosclerosis and glomerular nephropathy (proteinuria, hyperuricemia). Other markers such as PP13 and PTX3 seem of interest even if their functions are poorly understood. Preeclampsia develops on a predisposed maternal environment (genetic, epigenetic infectious, and endocrine factors) characterized by a maternal inadequacy to pregnancy.
