First-trimester prediction of preterm prelabour rupture of membranes incorporating cervical length measurement.

OBJECTIVES: To examine early pregnancy risk factors for preterm prelabour rupture of membranes (PPROM) and develop a predictive model. STUDY DESIGN: Retrospective analysis of a cohort of mixed-risk singleton pregnancies screened in the first and second trimesters in three Danish tertiary fetal medicine centres, including a cervical length measurement at 11-14 weeks, at 19-21 weeks and at 23-24 weeks of gestation. Univariable and multivariable logistic regression analyses were employed to identify predictive maternal characteristics, biochemical and sonographic factors. Receiver operating characteristic (ROC) curve analysis was used to determine predictors for the most accurate model. RESULTS: Of 3477 screened women, 77 (2.2%) had PPROM. Maternal factors predictive of PPROM in univariable analysis were nulliparity (OR 2.0 (95% CI 1.2-3.3)), PAPP-A < 0.5 MoM (OR 2.6 (1.1-6.2)), previous preterm birth (OR 4.2 (1.9-8.9)), previous cervical conization (OR 3.6 (2.0-6.4)) and cervical length ≤ 25 mm on transvaginal imaging (first-trimester OR 15.9 (4.3-59.3)). These factors all remained statistically significant in a multivariable adjusted model with an AUC of 0.72 in the most discriminatory first-trimester model. The detection rate using this model would be approximately 30% at a false-positive rate of 10%. Potential predictors such as bleeding in early pregnancy and pre-existing diabetes mellitus affected very few cases and could not be formally assessed. CONCLUSIONS: Several maternal characteristics, placental biochemical and sonographic features are predictive of PPROM with moderate discrimination. Larger numbers are required to validate this algorithm and additional biomarkers, not currently used for first-trimester screening, may improve model performance.

Increasing maternal age is not a significant cause of false-positive results for monosomy X in non-invasive prenatal testing.

OBJECTIVE: The accuracy of cell-free DNA aneuploidy screening varies by the chromosome assessed. The positive predictive value is consistently low for monosomy X (MX), at less than 30%. This study aims to investigate maternal age and other possible predictors of false-positive MX screening results in order to guide pre-test and post-test counselling. METHODS: A total of 52 499 NIPT samples were tested over 69 months, across three specialist obstetric services. Outcome data were available for 96 out of 107 cases high risk for MX. Cytogenetic outcomes were compared to clinical and demographic data to look for trends that may indicate higher likelihood of a false-positive NIPT result. RESULTS: The likelihood of a false-positive MX result significantly increased with the absence of ultrasound features suggestive of MX and with lower PAPP-A levels. Non-significant trends towards false-positive results were identified with increased maternal age, increased body mass index and Caucasian ethnicity. CONCLUSION: Maternal age is not a reliable predictor of a false-positive result. Assessment of ultrasound findings and placental serology in the first trimester is important for appropriate post-test counselling and should continue to be a part of screening even when NIPT is used as a first-tier screening test.

Discordant fetal sex on NIPT and ultrasound.

Prenatal diagnosis of sex discordance is a relatively new phenomenon. Prior to cell-free DNA testing, the diagnosis of a disorder of sexual differentiation was serendipitous, either through identification of ambiguous genitalia at the midtrimester morphology ultrasound or discovery of genotype-phenotype discordance in cases where preimplantation genetic diagnosis or invasive prenatal testing had occurred. The widespread integration of cfDNA testing into modern antenatal screening has made sex chromosome assessment possible from 10 weeks of gestation, and discordant fetal sex is now more commonly diagnosed prenatally, with a prevalence of approximately 1 in 1500-2000 pregnancies. Early detection of phenotype-genotype sex discordance is important as it may indicate an underlying genetic, chromosomal or biochemical condition and it also allows for time-critical postnatal treatment. The aim of this article is to review cfDNA and ultrasound diagnosis of fetal sex, identify possible causes of phenotype-genotype discordance and provide a systematic approach for clinicians when counseling and managing couples in this circumstance.

Influence of Body Mass Index on Fetal Fraction Increase With Gestation and Cell-Free DNA Test Failure.

OBJECTIVE: To assess the influence of body mass index (BMI) on fetal fraction increase with gestational age and on the rates of test failure. METHODS: We performed a cross-sectional study of consecutive singleton pregnancies in which cell-free DNA screening for fetal aneuploidies was performed from 10 weeks of gestation, between May 2013 and January 2018, at two fetal medicine clinics in Australia using one of two different platforms. Maternal characteristics, fetal fraction, and failure after a first attempt ("no-call") and after resampling ("test failure") were recorded. Body mass index was classified as normal (BMI less than 25.0), overweight (BMI 25.0-29.9), obesity class I (BMI 30.0-34.9), and obesity classes II and III (BMI 35.0 or greater). Fetal fraction and proportions of no-call results and test failure were compared between the groups. RESULTS: Of 14,223 singleton pregnancies included, 8,583 (60.3%) were screened with platform A and 5,640 (39.7%) with platform B. Median fetal fraction values were lower, and no-call and failure rates were higher in increased BMI groups across both platforms (P<.001 in both). When compared with women with normal BMIs, women with BMIs of 35 or greater had a significantly smaller increase in fetal fraction (0.1 vs 0.3 units/wk, P<.001, in both platforms). In this subgroup, when compared with women with normal BMIs, the odds ratios for a no-call result were 22.0 (95% CI 13.8-35.3, 16.6% vs 0.9%) and 8.0 (95% CI 4.1-15.6, 7.8% vs 1.0%) and for a failed test were 25.0 (95% CI 11.2-55.7, 6.4% vs 0.3%) and 5.8 (95% CI 2.0-17.3, 2.7% vs 0.5%) using platforms A and B, respectively. CONCLUSION: The increase in fetal fraction throughout gestation in women with BMIs of 35 or above is minimal. Postponing the test is unlikely to reduce test failure rates in this population.

Cell-free fetal DNA testing in singleton IVF conceptions.

STUDY QUESTION: Are fetal fraction, test failure rate and positive predictive value (PPV) of cell-free fetal DNA (cffDNA) testing different in singleton IVF conceptions compared to spontaneous conceptions? SUMMARY ANSWER: Fetal fraction is significantly lower; test failure rate is higher and PPV of cffDNA testing is lower in singleton pregnancies conceived by IVF than those conceived spontaneously. WHAT IS ALREADY KNOWN: cffDNA testing, which analyses circulating cffDNA in maternal blood, has very high accuracy for detection of trisomy 21 in the general obstetric population. Focused and conclusive evidence regarding the test characteristics of cffDNA testing in IVF conceived pregnancies is lacking. STUDY DESIGN, SIZE, DURATION: This was a retrospective cohort study including spontaneously and IVF conceived singleton pregnancies collected consecutively between April 2013 and November 2016. A total of 4633 spontaneously conceived and 992 IVF pregnancies were included. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was performed at an obstetric and gynecological ultrasound clinic in Melbourne, Australia. Participants had screening for trisomies 21, 18 and 13, as well as sex chromosome aneuploidies (SCA) performed with cffDNA testing after 10 weeks' gestation. Multivariate regression analysis was used to determine significant predictors of logarithmically transformed fetal fraction and test failure. Comparison of test characteristics between study groups was performed adopting a significance level of 5%. MAIN RESULTS AND THE ROLE OF CHANCE: Median fetal fraction was lower (10.3% [interquartile range (IQR), 7.7-13.5] versus 11.9% [IQR, 9.1-15.0]; P = 0.005), test failure rate was higher (5.2 versus 2.2%; P < 0.001) and positive predictive value (PPV) for trisomies 18, 13 and SCA was poorer in IVF pregnancies compared to those spontaneously conceived. Multivariate linear regression analysis demonstrated that IVF conception, increased BMI, earlier gestational age and South and East Asian ethnicities were independent predictors of lower fetal fraction. Multiple logistic regression analysis found IVF conception and increased BMI to be independently associated with test failure. PPV was high for trisomy 21 in IVF conception (100.0%), but was lower for other trisomies when compared with the non-IVF population. LIMITATIONS REASONS FOR CAUTION: IVF details were unascertainable for 210 cases, as the information was not available through our data collection points. Inability to karyotype some cases at high-risk for SCA, due to patients' choice, and the occurrence of miscarriages and terminations, resulted in the exclusion of high-risk cases when calculating PPV. Pregnancy outcomes were not available in low-risk pregnancies and negative predictive values could not be calculated. WIDER IMPLICATIONS OF THE FINDINGS: The limitations revealed by this work should be taken into account during pre-test counseling in pregnant women who conceive by IVF. STUDY FUNDING/COMPETING INTEREST(S): No external source of financial support was provided for this research. The authors report no conflicts of interest.

Sex discordance identification following non-invasive prenatal testing.

OBJECTIVE: The objectives of this study were to characterise genotype-phenotype discordance identified in the routine clinical setting and to explore the associated diagnostic and counselling challenges. METHOD: Cases were derived from a cohort of pregnant women who attended a multisite specialist prenatal screening and ultrasound service for non-invasive prenatal testing by cell-free DNA analysis and midtrimester fetal morphology assessment. RESULTS: Seven cases of genotype-phenotype discordance were identified from a cohort of 12 919 women between June 2013 and March 2017 (incidence 1/1845 pregnancies). A variety of disorders of sexual differentiation were subsequently diagnosed. CONCLUSION: Sex chromosomes are the basis of sexual differentiation during embryonic development. Variations of the traditional XX or XY karyotype may result in conditions where the genotype is discordant with the phenotype. Detection of these conditions in the past typically occurred during adolescence, due to delayed puberty, or during adulthood, due to infertility. With the increasing availability of non-invasive prenatal testing and high-resolution ultrasound, more cases of genotype-phenotype sex discordance are being identified in routine clinical practice during early pregnancy. These discordant results present significant diagnostic and counselling challenges, and their potential should be included in increasingly complex pre-NIPT counselling.

Influence of sampling site on uterine artery Doppler indices at 11-13⁺6 weeks gestation.

INTRODUCTION: Uterine artery pulsatility index (PI) is a key variable in the first trimester screening for pre-eclampsia. The aims of the study were to examine the effect of sampling the uterine arteries at a site distal to the level of the internal os, and to determine a lower limit of peak systolic velocity (PSV) to establish an auditable standard. MATERIAL AND METHODS: PI and PSV measurements were performed at 11-13(+6) weeks' gestation at two sites: at the level of the internal os and 3 cm distal to the internal os. Comparative analyses utilised the Student's paired t-test. A 90% reference interval of transformed PSV measurements at the internal os was generated by polynomial regression. RESULTS: There was a significant reduction in both the PI (14.9%) and the PSV (17.4%) when measured at the distal site compared to the level of the internal os (both p < 0.001). The best estimated 5th centile for uterine artery PSV at 11-13(+6) weeks was 60.9 cm/s. CONCLUSION: PI measurements performed distal to the internal os are significantly lower and will result in inaccurate pre-eclampsia risk assessment. PSV measurements below 60 cm/s are likely to indicate an incorrect sampling site. Development of auditable measurement standards is important to ensure accuracy of prospective pre-eclampsia screening.

Uterine artery pulsatility index assessment at 11-13 weeks' gestation.

INTRODUCTION: First-trimester uterine artery pulsatility index (PI) measurements form part of an algorithm used to assess the risk of developing pre-eclampsia. The objective of this study was to construct a population-specific reference range for both the lower and mean maternal uterine artery PI at 11-13(+6) weeks' gestation and to assess measurement agreement. MATERIALS AND METHODS: Reference ranges for mean and lower PI measurements were developed using polynomial regression models following prospective collection of maternal uterine artery PI measurements at 11-13(+6) weeks' gestation. Measurement agreement studies were performed by two experienced operators. RESULTS: Measurements from 298 women were included in the primary study. Polynomial regression indicated no change over gestational age for the lower PI (mean 1.44). There was an inverse relationship between the average PI and gestational age (mean [0.8960 + (2.9771 × CRL(-1/2))]2). PI measurement agreement was good-strong (intraclass correlation (ICC) 0.50-0.79) between operators, and within-operator agreement was almost perfect (ICC 0.88-0.93). CONCLUSIONS: Reference ranges for both the average and lowest PI of the maternal uterine arteries were derived at 11-13(+6) weeks' gestation. This will provide a basis for development of auditable standards for first-trimester uterine artery Doppler measurements. The PI measurements are reproducible and reliable.

Auditing ultrasound assessment of fetal nuchal translucency thickness: a review of Australian National Data 2002-2008.

BACKGROUND: Nuchal translucency (NT) measurement is the ultrasound component of first trimester combined screening for Down syndrome. In 2002, a NT ultrasound education and monitoring program was established in Australia. Between 2002 and 2008, a total of 728,502 NT scans were audited through this process. OVERALL AIM: To audit the availability and performance of certified operators measuring NT following implementation of the Australian education and monitoring program in 2002. METHODS: Retrospective review of the central database that is used to monitor performance of individuals and practices performing NT scans in both public and private practice settings throughout Australia between 2002 and 2008. The performance of operators was assessed by a widely used international standard - that 40-60% of NT measurements should be above the median value for gestational age. RESULTS: The number of certified operators has increased (from 184 in 2002 to 477 in 2008). There is wide variation between states in the number of operators per birth. The percentage of certified operators with a measurement distribution meeting the international standard has increased from 40% in 2002 to 55% in 2008. Greatest improvement has been seen in operators performing 30-199 scans per year. There has been no overall improvement in performance over the last three audit cycles. CONCLUSIONS: The number of operators certified to perform the NT scan has increased since 2002, although availability in some states remains low. An initial improvement in performance of operators appears to have reached a plateau. It is time to become more proactive in engaging operators in the audit cycle.