Biochemical markers for the prediction of preterm birth

Cytokine networks and the regulation of uterine function in pregnancy and parturition

Complex cytokine networks play an important role in a wide range of reproductive and pregnancy related processes. Here, we review the current knowledge concerning the impact of cytokines on uterine physiology and pathophysiology. Cytokines influence a range of uterine functions during the menstrual cycle, implantation, pregnancy and labour. The synergistic interactions between individual cytokines are intricate and dynamic, and modulated by pregnancy hormones. It is not surprising therefore, that perturbations to cytokine signalling are associated with adverse pregnancy outcomes, such as miscarriage, pre-eclampsia, preterm labour and foetal brain injury. Further insight into the complexity of cytokine networks will be required to develop novel therapeutic strategies for the treatment of cytokine imbalances in pregnancy.

Epidemiology and causes of preterm birth

This paper is the first in a three-part series on preterm birth, which is the leading cause of perinatal morbidity and mortality in developed countries. Infants are born preterm at less than 37 weeks' gestational age after: (1) spontaneous labour with intact membranes, (2) preterm premature rupture of the membranes (PPROM), and (3) labour induction or caesarean delivery for maternal or fetal indications. The frequency of preterm births is about 12-13% in the USA and 5-9% in many other developed countries; however, the rate of preterm birth has increased in many locations, predominantly because of increasing indicated preterm births and preterm delivery of artificially conceived multiple pregnancies. Common reasons for indicated preterm births include pre-eclampsia or eclampsia, and intrauterine growth restriction. Births that follow spontaneous preterm labour and PPROM-together called spontaneous preterm births-are regarded as a syndrome resulting from multiple causes, including infection or inflammation, vascular disease, and uterine overdistension. Risk factors for spontaneous preterm births include a previous preterm birth, black race, periodontal disease, and low maternal body-mass index. A short cervical length and a raised cervical-vaginal fetal fibronectin concentration are the strongest predictors of spontaneous preterm birth.

Genetic contributions to preterm birth: implications from epidemiological and genetic association studies

Infants born before term (<37 weeks) have an increased risk of neonatal mortality as well as other health problems. The increasing rate of preterm birth in recent decades, despite improvements in health care, creates an impetus to better understand and prevent this disorder. Preterm birth likely depends on a number of interacting factors, including genetic, epigenetic, and environmental risk factors. Genetic studies may identify markers, which more accurately predict preterm birth than currently known risk factors, or novel proteins and/or pathways involved in the disorder. This review summarizes epidemiological and genetic studies to date, emphasizing the complexity of genetic influences on birth timing. While several candidate genes have been reportedly associated with the disorder, inconsistency across studies has been problematic. More systematic and unbiased genetic approaches are needed for future studies to examine the genetic etiology of human birth timing thoroughly.

PAPP-A levels as an early marker of idiopathic preterm birth: a pilot study

OBJECTIVE

To evaluate late PAPP-A levels as predictive of preterm birth in symptomatic women.

STUDY DESIGN

Prospective cohort study of singleton gestations, 23 to 34 weeks, and symptoms of preterm labor. PAPP-A, IGF-I and IGF-III analysis were performed. Primary end point was delivery < or =7 days. Accuracy and optimally predictive PAPP-A values were based on receiver operator characteristic (ROC) curves.

RESULT

In all, 26 women (51%) delivered < or =7 days post-admission (Group 1); 25 women (49%) >7 days (Group 2). Group 1 mean PAPP-A=38 000 vs 55 333 for Group 2 (P<0.04). Group 1 mean gestational age at delivery=29 weeks vs 37 weeks for Group 2 (P<0.00014). PAPP-A level < or =30,000 mU l(-1) had highest specificity (88%), sensitivity (50%), and positive predictive (81%) and negative predictive (62%) values for delivery < or =7 days. ROC area under curve=0.703.

CONCLUSION

PAPP-A levels < or =30,000 mU l(-1) at admission was associated with increased risk for preterm birth < or =7 days, supporting active management and therapeutic approach in these women.

A translational approach to studying preterm labour

Preterm labour continues to be a major contributor to neonatal and infant morbidity. Recent data from the USA indicate that the number of preterm deliveries (including those associated with preterm labour) has risen in the last 20 years by 30%. This increase is despite considerable efforts to introduce new therapies for the prevention and treatment of preterm labour and highlights the need to assess research in this area from a fresh perspective. In this paper we discuss i) the limitations of our knowledge concerning prediction, prevention and treatment of preterm labour and ii) future multidisciplinary strategies for improving our approach.

Reductionist and system approaches to study the role of infection in preterm labor and delivery

A substantial number of patients with preterm labor and delivery do not show clinical signs of infection, however, it is the subclinical form which is the main causative factor and often results in premature delivery. The hitherto commonly applied methods of inflammation detection are based either on potentially hazardous amniocentesis or still insufficient inflammation-related protein measurement in the serum or other biological fluids. The advent of new "omics" technologies has led to a paradigm-shift in experimental approach which tends to primarily generate rather than form hypotheses. This has resulted in a surge of wealth of data composed of sets of individual or clusters of new genes and proteins that can be of potential importance as new markers of inflammation leading to preterm labor. It is hoped that as a result of those new methodologies the overall perception of medical research and practice would gradually change from reductionist to systems approach. Despite several successes of reductionism in the diagnosis and treatment of preterm labor it seems that system-based methodology would contribute to a more favorable personalized rather than one-for-all patient assistance. In this review we present the current knowledge on this new attractive field of medical studies with emphasis on early detection of infection related with preterm labor.

A systematic review and quality assessment of systematic reviews of fetal fibronectin and transvaginal length for predicting preterm birth

This systematic review aims to identify reviews of fetal fibronectin and transvaginal cervical length for predicting preterm birth, so that these could be appraised and the findings from good quality reviews highlighted. Reviews, rather than individual studies, are the basis for this systematic review because of the proliferation of reviews and the benefits of a single, consistent appraisal and assessment of evidence from these reviews, rather than further attempts to find and appraise the many individual studies in the literature. Potentially eligible reviews were sought primarily through searches of the electronic databases MEDLINE (1966-2005), EMBASE (1980-2005), CINHAL (1982-2005), Science Citation Index (1970-2005) and The Cochrane Library (Issue 3, 2005). Our systematic review consists of a description of the two factors that might be predictive of preterm birth and for which at least one relevant review was found. The scope and quality of the identified review(s) are described, and their conclusions and the strength of these conclusions discussed. Ten reviews were identified, of which seven were included in this systematic review of reviews. The quality of each review is assessed within the following domains; the extent of searching undertaken, description of study selection and inclusion criteria, comparability of included studies, assessment of publication bias, assessment of heterogeneity and conduct of sensitivity analyses. The reviews we identified show that cervicovaginal fetal fibronectin and transvaginal sonographic cervical length measurements are clinically useful factors in predicting preterm birth. Consideration might be given to the use of both the measurement of cervicovaginal fetal fibronectin and transvaginal sonographic assessment of cervical length to identify women at increased risk of preterm birth and, potentially, to improve the outcome for these women and their babies.

Fetal Adrenal Gland Volume

OBJECTIVE

To investigate the risk of preterm birth (delivery at less than 37 weeks of gestation) by evaluating the fetal adrenal gland volume, hallmark of activation of the fetal hypothalamic-pituitary-adrenal axis, measured by 3-dimensional ultrasonography.

METHODS

We performed 3-dimensional ultrasound examination of the fetal adrenal gland volume in 126 singleton fetuses, prospectively comparing those born to mothers with signs or symptoms of preterm labor (n=53) to control subjects (n=73). Multiplanar technique with rotational methods for measurement of fetal adrenal gland volume was performed by using Virtual Organ Computer-Aided Analysis (VOCAL) technology.

RESULTS

The fetal adrenal gland volume was successfully examined in 86.5% of the cases. There was a direct relationship between the fetal adrenal gland volume and estimated fetal weight. A corrected adrenal gland volume of greater than 422 mm3/kg was best in predicting preterm birth within 5 days from the time of the measurement. The sensitivity, specificity, and positive and negative likelihood ratios were 92%, 99%, 93.5, and 0.08, respectively. Multiple logistic regression analysis showed that the corrected adrenal gland volume was the only significant independent predictor factor of preterm birth within 5 days of measurement.

CONCLUSION

Corrected adrenal gland volume measurement may identify women at risk for impending preterm birth. This information can be generated noninvasively and in time for clinical decision making.

LEVEL OF EVIDENCE

II.

Methods for samples preparation in proteomic research

Sample preparation is one of the most crucial processes in proteomics research. The results of the experiment depend on the condition of the starting material. Therefore, the proper experimental model and careful sample preparation is vital to obtain significant and trustworthy results, particularly in comparative proteomics, where we are usually looking for minor differences between experimental-, and control samples. In this review we discuss problems associated with general strategies of samples preparation, and experimental demands for these processes.

Identification of novel protein biomarkers of preterm birth in human cervical-vaginal fluid

Spontaneous preterm birth (SPTB) is a major contributor to perinatal morbidity and mortality. However, the diagnosis of preterm labor (PTL) that leads to preterm birth is difficult, and there is a pressing need for improved diagnosis. We utilized multidimensional liquid chromatography-tandem mass spectrometry (LC/LC-MS/MS; MudPIT) and Fluorescence two-dimensional differential in-gel electrophoresis (2D-DIGE) to identify potential biomarkers of PTL and SPTB. MudPIT analysis identified 205 proteins in cervical-vaginal fluid (CVF), 28 of which exhibited significant differences in pairwise and progressive comparisons. Calgranulins, annexins, S100 calcium-binding protein A7, and epidermal fatty acid binding protein were abundant in CVF and differentially present in PTL and SPTB samples, as were the serum proteins alpha-1-antitrypsin, alpha1-acid glycoprotein, haptoglobin, serotransferrin, and vitamin D binding protein. 2D-DIGE identified 17 proteins that were significantly differentially present in PTL and SPTB. Immunoblotting with specific antibodies confirmed the differences and trends of selected markers. Further characterization and quantification of these markers in a larger cohort of subjects may provide the basis for new tests for the early, noninvasive positive prediction of SPTB.

Prediction of preterm delivery among women with threatened preterm labor

BACKGROUND/AIMS

To determine predictive values of fetal fibronectin and phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) in cervicovaginal secretions and ultrasonographic measurement of cervical length for delivery <35 weeks in patients with uterine contractions.

METHODS

Our study included 51 women between 24 and 35 weeks' gestation with uterine contractions and 90 controls. Cervicovaginal samples were analyzed for presence of fetal fibronectin and phIGFBP-1. Cervical length was measured by transvaginal sonography.

RESULTS

Preterm birth rate was 19.6% (10/51) in the study group. Negative predictive values of fetal fibronectin, phIGFBP-1 and ultrasonographic cervical length <20 mm, and <25 mm for delivery <35 weeks were 91.9, 92.3, 91.1, and 90.5%, respectively. Positive predictive values were 50, 58.3, 100 and 66.7%, respectively. When results of fetal fibronectin/phIGFBP-1 test and ultrasonographic cervical length <25 mm were combined, specificity and positive predictive values of each test for delivery within 7 days increased.

CONCLUSION

Fetal fibronectin and phIGFBP-1 tests have approximately equivalent ability to predict delivery <35 weeks' gestation. An ultrasonographic cervical length measurement >20 mm or a negative fetal fibronectin/phIGFBP-1 test obtained from patients with uterine contractions at 24-35 weeks' gestation may avoid overdiagnosis.

Low birth weight in the United States

Pregnancy outcomes in the United States and other developed countries are considerably better than those in many developing countries. However, adverse pregnancy outcomes are generally more common in the United States than in other developed countries. Low-birth-weight infants, born after a preterm birth or secondary to intrauterine growth restriction, account for much of the increased morbidity, mortality, and cost. Wide disparities exist in both preterm birth and growth restriction among different population groups. Poor and black women, for example, have twice the preterm birth rate and higher rates of growth restriction than do most other women. Low birth weight in general is thought to place the infant at greater risk of later adult chronic medical conditions, such as diabetes, hypertension, and heart disease. Of interest, maternal thinness is a strong predictor of both preterm birth and fetal growth restriction. However, in the United States, several nutritional interventions, including high-protein diets, caloric supplementation, calcium and iron supplementation, and various other vitamin and mineral supplementations, have not generally reduced preterm birth or growth restriction. Bacterial intrauterine infections play an important role in the etiology of the earliest preterm births, but, at least to date, antibiotic treatment either before labor for risk factors such as bacterial vaginosis or during preterm labor have not consistently reduced the preterm birth rate. Most interventions have failed to reduce preterm birth or growth restriction. The substantial improvement in newborn survival in the United States over the past several decades is mostly due to better access to improved neonatal care for low-birth-weight infants.

Preterm labour: update on prediction and prevention strategies

PURPOSE OF REVIEW

The incidence of preterm birth is increasing and continues to be a significant cause of neonatal mortality and morbidity. Techniques now exist that can accurately predict early birth. Prevention can therefore be targeted, although effective measures that improve outcome are yet to be established.

RECENT FINDINGS

Obtaining an accurate history is the first step in identifying high-risk women. Clinicians then rely on other predictors such as fetal fibronectin, cervical length assessment and biochemical markers. Research should focus on the combination of noninvasive markers targeted at high-risk women as a screening tool, determining not only appropriate diagnostic levels for positive tests, but also sufficiently large studies should be performed to determine the predictive values of these tests. Interventions to prevent delivery and improve neonatal outcome remain unsatisfactory, mainly comprising tocolysis, cerclage, progesterone and, in some cases, antibiotics. Women who would most benefit from these interventions are difficult to identify and an appreciation of the pathophysiology in an individual woman, such as the relevance of the inflammatory status of the endocervix, may be important in tailoring intervention.

SUMMARY

An improved understanding of the mechanisms underlying the pathological process in preterm birth will allow screening and interventions to be appropriately targeted.

Genetic associations in preterm birth: a primer of marker selection, study design, and data analysis

Spontaneous preterm birth (PTB; delivery before 37 weeks gestation) is a primary risk factor for infant morbidity and mortality. The etiology is unclear, but there is evidence that there is a genetic predisposition to PTB. Armed with the suggestion of genetic risk factors and the failure to identify useful biomarkers, investigators are starting to actively pursue the role of genetic predisposition in PTB. Several studies have been done to date assessing the role of single gene variants. However, positive findings have failed to replicate. We argue that heterogeneity in study designs, definition of phenotype, single-nucleotide polymorphism (SNP) selection, population selection, and sample size makes data interpretation difficult in complex phenotypes such as PTB. In this review, we introduce general concepts of study designs in genetic epidemiology, selection of candidate genes and markers for analysis, and analytical methodologies. We also introduce how the concept of gene-gene interactions (biologic epistasis) and gene-environment interactions may affect the predisposition to PTB.

Maternal and biochemical predictors of spontaneous preterm birth among nulliparous women: a systematic analysis in relation to the degree of prematurity

BACKGROUND

Nulliparous women are at increased risk of spontaneous preterm birth. Other maternal and biochemical risk factors have also been described. However, it is unclear whether these associations are strong enough to offer clinically useful prediction. It is also unclear whether the predictive power of these factors varies in relation to the degree of prematurity.

METHODS

The risk of spontaneous preterm birth associated with maternal characteristics and second trimester serum screening data was analysed in a dataset of 84 391 first births in Scotland between 1992 and 2001 using Cox and logistic regression. Variation in the relative risk of preterm birth over the period 24-36 weeks was assessed using a test of the proportional hazards assumption.

RESULTS

The risk of spontaneous preterm birth was positively associated with maternal serum levels of alpha-fetoprotein, socioeconomic deprivation, number of previous therapeutic abortions, smoking, and being unmarried and was negatively associated with height and body mass index. The risk of preterm birth at 24-28 weeks, but not later gestations, was increased in association with maternal levels of human chorionic gonadotrophin >95th percentile, maternal age <20, and two or more previous miscarriages. The area under the receiver operating characterise curve (95% CI) for models based on these factors was 0.67 (0.63-0.71) for 24-28 weeks, 0.65 (0.62-0.68) for 29-32 weeks, and 0.62 (0.61-0.63) for 33-36 weeks.

CONCLUSIONS

Time to event analytic methods can identify factors that are differentially associated with spontaneous preterm birth according to the degree of prematurity. However, models based on maternal and biochemical data perform poorly as a screening test for any degree of spontaneous preterm birth.