Overview of Noninvasive Prenatal Testing (NIPT) for the Detection of Fetal Chromosome Abnormalities; Differences in Laboratory Methods and Scope of Testing

Although nearly all noninvasive prenatal testing is currently based on analyzing circulating maternal cell-free DNA, the technical methods usedvary considerably. We review the different methods. Based on validation trials and clinical experience, there are mostly relatively small differences in screening performance for trisomies 21, 18, and 13 in singleton pregnancies. Recent reports show low no-call rates for all methods, diminishing its importance when choosing a laboratory. However, method can be an important consideration for twin pregnancies, screening for sex chromosome abnormalities, microdeletion syndromes, triploidy, molar pregnancies, rare autosomal trisomies, and segmental imbalances, and detecting maternal chromosome abnormalities.

Prenatal diagnosis of micrognathia: a systematic review

Purpose

This systematic review aimed to analyze the characteristics of different diagnostic techniques for micrognathia, summarize the consistent diagnostic criteria of each technique, and provide a simple and convenient prenatal diagnosis strategy for micrognathia.

Methods

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, the search was undertaken in three international databases (PubMed, Scopus, and Web of Science). The three reviewers assessed all papers and extracted the following variables: author's name and year of publication, country, study design, number of participants, gestational age, equipment for prenatal examination, biometric parameters related to micrognathia, main results.

Results

A total of 25 articles included in the analysis. Nineteen articles described cross-sectional studies (76 percent), 4 (16 percent) were case-control studies, and 2 (8 percent) were cohort studies. Fifteen studies (60 percent) had a prospective design, 9 (36 percent) had a retrospective design, and one (4 percent) had both prospective and retrospective design. Thirty-two percent of the studies (n = 8) were performed in USA, and the remaining studies were performed in China (n = 4), Israel (n = 3), Netherlands (n = 3), UK (n = 1), France (n = 1), Italy (n = 1), Belgium(n = 1), Germany (n = 1), Spain (n = 1), and Austria (n = 1). The prenatal diagnosis of micrognathia can be performed as early as possible in the first trimester, while the second and third trimester of pregnancy were the main prenatal diagnosis period. The articles that were included in the qualitative synthesis describe 30 biometric parameters related to the mandible.

Conclusion

Of the 30 biometric parameters related to the mandible, 15 can obtain the simple and convenient diagnostic criteria or warning value for micrognathia. Based on these diagnostic criteria or warning value, clinicians can quickly make a preliminary judgment on facial deformities, to carry out cytologic examination to further clarify the diagnosis of micrognathia.

Non‐invasive prenatal screening for fetal triploidy using single nucleotide polymorphism (SNP)‐based testing: Differential Diagnosis And Clinical Management In Cases Showing An Extra Haplotype

Objective

An extra haplotype is infrequently encountered in single nucleotide polymorphism(SNP)‐based non‐invasive prenatal testing (NIPT) and is usually attributed to an undetected twin or triploidy. We reviewed a large series to establish relative frequencies of these outcomes and identify alternative causes.

Methods

In 515,804 women receiving NIPT from September 2017 through March 2019, all results with an extra haplotype were reviewed. Known viable and vanished twin pregnancies were excluded. For positive cases, pregnancy outcome information was sought.

Results

Of 1005 results with an extra haplotype (1 in 513), pregnancy outcome was available for 773 cases: 11% were confirmed or suspected triploidy; 65% to vanished twin; 10% with pregnancy loss. Rare explanations included complete mole, chimera, undisclosed donor egg pregnancy, maternal organ transplant and one instance of maternal neoplasm. Among triploid cases that were detected and independently confirmed, 23/27 (85%) were diandric.

Conclusion

SNP‐based NIPT, with detection of an extra haplotype, is 11% predictive of triploidy. For results with an extra haplotype, ultrasound is recommended to establish viability, evaluate for twins (viable or vanished), and detect findings consistent with triploidy. Review of patient history, serum screening, and ultrasound will reduce the number of CVS or amniocenteses necessary to confirm a diagnosis of triploidy.

What's already known about this topic?

Both digynic and diandric triploidy are occasionally seen in pregnancies but are extremely rare in live‐births

In cell‐free DNA prenatal screening, the presence of an extra haplotype could be indicative of either twin pregnancy or triploidy

What does this study add?

Outcomes for a large series of prenatal screening tests where an extra haplotype was identified in cell‐free DNA

Complete moles, chimeras, transplantation, and donor egg are additional explanations for extra haplotypes

We discuss prenatal management when an extra haplotype is observed in cell‐free DNA

Fetal Crown-Chin Length to Crown-Rump Length Ratio as a Prenatal Sonographic Marker for Triploidy at First Trimester

OBJECTIVES

To investigate the ratio of Crown to Chin length (CCL) to Crown-rump length (CRL) between triploid and normal fetuses at first trimester and establish a reference range of fetal CCL/CRL ratio.

METHODS

Three hundred and twenty-five normal and 12 triploid fetuses were reviewed in this study. The image of fetal Crown-rump length (CRL) was acquired retrospectively. CCL and CRL were measured offline by two experienced sonographers, we obtained each averaged value of CCL and CRL as the final data for analysis. A normal range of CCL was established and CCL/CRL ratio was analyzed in normal and triploid fetuses.

RESULTS

In 325 normal fetuses, CCL increased with gestational age following a linear trend from 20 mm at a CRL of 45-36 mm at a CRL of 84 mm (CCL (mm) = 3.65 + 0.38 CRL, R²  = 0.821, P = .000). The CCL/CRL ratio decreased with gestational age from a mean of 0.46 at a CRL of 45 mm to 0.41 at a CRL of 84 mm (PML/CRL = 0.502-0.001 CRL, R²  = 0.093, P = .000). All 12 triploid fetuses had a CCL/CRL ratio above the 95th percentile. When the 95th percentile are used as cutoff values, the detection rate, false-positive rate, and the positive likelihood ratio are 100%, 5%, and 20, respectively.

CONCLUSIONS

The present study demonstrates that fetal CCL/CRL ratio can be used and effective ultrasound marker in screening for triploidy during the first trimester.

Twin pregnancies discordant for digynic triploidy - A case series

OBJECTIVE

To analyse natural course and perinatal management in twin pregnancies discordant for digynic triploidy.

CASE REPORT

We present five cases of twins discordant for digynic triploidy. Pregnancy outcome was known for three of them. In one case, premature rupture of membranes occurred at 20 gestational weeks and both fetuses were miscarried. In two other pregnancies healthy co-twins were born at term after the triploid fetuses demise at 28 and 37 weeks. No maternal complications were observed.

CONCLUSION

Twin pregnancies discordant for triploidy poses a challenge for perinatal management. Expectant management should be considered in digynic triploid cases.

Prenatal diagnosis of syndromic alobar holoprosencephaly associated with digynic triploidy fetus

Holoprosencephaly (HPE) is a dramatic human brain malformation sequence with an extreme variable phenotypic spectrum and genetic heterogeneity, variable degree of severity and unknown etiology, in many cases. HPE is classified into syndromic, chromosomal, and non-syndromic, non-chromosomal. The most cases of HPE are syndromic. We present an atypical case of syndromic alobar HPE associated with digynic triploidy fetus, prenatally diagnosed, early at 18 weeks of gestation, by ultrasound (US) and complex genetic investigations. The US examination was performed with a specialized US machine, General Electric Voluson E10 OLED BT18, using two-dimensional (2D) scanning, three-dimensional (3D) image reconstruction, four-dimensional (4D) spatiotemporal image methodology and the highest power Doppler US technology. A detailed US examination of the fetus revealed several major abnormalities of the fetal head and severe facial malformations. Based on the antenatal US findings, the fetus was diagnosed with alobar HPE. After a careful examination and genetic counseling, additional cytogenetic investigations and molecular genetic analyses were performed, which revealed an abnormal number of 69 chromosomes, digynic triploidy (69,XXY). Two days later, the parents choose to interrupt the current gestation because of major fetal malformations. The pathological examination of the embryo reaffirmed the antenatal diagnostics.

Triploid pregnancy-Clinical implications

Triploidy is a life-limiting genetic aberration resulting from an extra haploid set of chromosomes of paternal (diandric triploidy) or maternal origin (digynic triploidy). Triploidy affects around 1%-2% of all conceptions. The majority of cases is miscarried at early developmental stages. In consequence of genomic imprinting, parental origin affects the phenotype of triploid pregnancies as well as the prevalence and spectrum of related maternal complications. Distinctive ultrasound features of both triploid phenotypes as well as characteristic patterns of biochemical markers may be useful in diagnosis. Molecular confirmation of the parental origin allows to predict the risk of complications, such as gestational trophoblastic neoplasia, hyperthyroidism, hypertension, or preeclampsia associated with the paternal origin of triploidy. Diagnosis of partial hydatidiform mole associated with diandric triploidy is challenging especially in the first trimester pregnancy loss due to the limitations of both histopathology and ultrasound. We present important clinical aspects of triploid pregnancies and indicate unresolved issues demanding further studies.

Recurrent fetal triploidy: is there a genetic cause?

Triploidy is currently understood as a sporadic genetic disorder, with no recognisable risk of recurrence nor identifiable risk factors. In cases of triploidy, chances of thriving through the second trimester of fetal development are very slim, with most of these pregnancies ending as early miscarriage. We report a case of repeated triploid pregnancies in the same woman, from different fathers, achieving the second trimester of pregnancy; elective termination was decided in both cases, after an amniocentesis revealing a triploid karyotype. Both triploid pregnancies are described and compared; prenatal laboratorial markers, sonographic features, clinical course and pathological findings are analysed and matched with fetal autopsy and placental pathological study. Reported findings strongly point to recurrent triploidy of maternal origin, and so the possibility of a genetic predisposition should be considered. Investigation is required to assess the presence of an underlying genetic mechanism in this setting, thus enabling a better genetic/obstetric counselling.

Maternal complications of fetal triploidy: a case report

A 32-year-old woman underwent a medical termination in the second trimester of a spontaneously conceived triploid pregnancy after developing early-onset preeclampsia with subsequent haemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. Placental histology was normal (non-molar) and unusually, she developed ovarian hyperstimulation syndrome (OHSS) 4 weeks later. She was managed conservatively following multidisciplinary team input to exclude malignant pathology. The rarity of late-onset spontaneous OHSS could have resulted in inappropriate surgical management. In the absence of supportive treatment there is also a risk of the condition progressing to a critical stage. Follow-up ultrasonography after termination of pregnancy should be considered for women with evidence of ovarian hyperstimulation, particularly if other risk factors for OHSS are present. Delayed-onset OHSS should be considered in women presenting with bilateral cystic ovarian enlargement after triploid pregnancy.

Prenatal sonographic features can accurately determine parental origin in triploid pregnancies

Objective

To describe the prenatal sonographic features and maternal biochemical markers in triploid pregnancies and to assess whether prenatal phenotype can determine genetic origin.

Methods

We performed a retrospective multicenter cohort study that included all triploid pregnancies diagnosed between 2000 and 2018 in two Fetal Medicine Units in Amsterdam. Fetal growth, presence of structural anomalies, extra‐fetal anomalies, and maternal biochemical markers were retrieved. Asymmetrical intrauterine growth restriction was diagnosed when the head‐to‐abdominal circumference (HC/AC) ratio was >95th centile. Parental origin was analyzed via molecular genotyping in 46 cases (38.3%).

Results

One hundred and twenty triploid pregnancies were identified, of which 86 cases (71.6%) were detected before 18 weeks of gestation. Triploidy of maternal origin was found in 32 cases (69.6%) and was associated with asymmetrical growth restriction, a thin placenta, and low pregnancy‐associated plasma protein A and free beta‐human chorionic gonadotrophin (β‐hCG) levels. Triploidy of paternal origin was found in 14 cases (30.4%) and was associated with an increased nuchal translucency, placental molar changes, and a high free β‐hCG. Prospective prediction of the parental origin of the triploidy was made in 30 of the 46 cases based on phenotypical ultrasound presentation, and it was correct in all cases.

Conclusion

Asymmetrical growth restriction with severe HC/AC discrepancy is pathognomonic of maternal triploidy. Placental molar changes indicate a paternal triploidy. Moreover, triploidy can present with an abnormal first trimester combined test, with serum levels on the extreme end. When available results of maternal serum markers can support the diagnosis of parental origin of the triploidy, an accurate assessment of the parental origin based on prenatal sonographic features is possible, making DNA analysis redundant.

First-Trimester Abdominal Circumference (Versus Crown Rump Length) Improves Precision in Inter- and Intraobserver Variability

OBJECTIVES

The aim of this study was to evaluate inter- and intraobserver variability of first-trimester biometric measurements and crown-rump length (CRL) and to compare the accuracy and precision of CRL with these biometric measurements used in the interpretation of first-trimester nuchal translucency (NT).

METHODS

Women presenting for a first trimester ultrasound were recruited. Both a sonographer, and a maternal fetal medicine specialist individually examined each participant. Each examiner obtained three independent measurements of CRL, a standardized set of biometric measurements (biparietal diameter, occipitofrontal diameter, head circumference, abdominal circumference, humerus length, and femur length), and an NT between 11 0/7 and 13 6/7 weeks of gestation. Biometry-specific expected NT values were calculated using linear and quadratic regression models and were used to convert results into multiples of the median.

RESULTS

Fetal biometric measurements, CRL, and NT measurements were obtained in 356 consecutive pregnancies with singleton fetuses. CRL demonstrated the least intra- and interobserver variability as demonstrated by the smallest coefficient of variance. However, abdominal circumference and head circumference were not statistically different from CRL variance. CRL and abdominal circumference showed the smallest standard deviation when calculating multiples of the median for NT interpretation.

CONCLUSION

First-trimester abdominal circumference demonstrates the most intra- and interobserver precision for dating and calculating NT multiples of the median, which could potentially be useful with obesity and in any setting with technical limitations of sonography.

A system-based approach to the genetic etiologies of non-immune hydrops fetalis

A wide spectrum of genetic causes may lead to nonimmune hydrops fetalis (NIHF), and a thorough phenotypic and genetic evaluation are essential to determine the underlying etiology, optimally manage these pregnancies, and inform discussions about anticipated prognosis. In this review, we outline the known genetic etiologies of NIHF by fetal organ system affected, and provide a systematic approach to the evaluation of NIHF. Some of the underlying genetic disorders are associated with characteristic phenotypic features that may be seen on prenatal ultrasound, such as hepatomegaly with lysosomal storage disorders, hyperechoic kidneys with congenital nephrosis, or pulmonary valve stenosis with RASopathies. However, this is not always the case, and the approach to evaluation must include prenatal ultrasound findings as well as genetic testing and many other factors. Genetic testing that has been utilized for NIHF ranges from standard chromosomal microarray or karyotype to gene panels and broad approaches such as whole exome sequencing. Family and obstetric history, as well as pathology examination, can yield additional clues that are helpful in establishing a diagnosis. A systematic approach to evaluation can guide a more targeted approach to genetic evaluation, diagnosis, and management of NIHF.

Prenatal sonographic diagnosis of biliary tract malformations

Congenital anomalies of the biliary tract include a variety of pathologic conditions, such as biliary atresia, choledochal cysts, gallbladder agenesis, congenital cholelithiasis, and gallbladder duplication. Although most of these malformations are rare and benign conditions, they may occasionally represent a major threat to extrauterine life. Visualization of a normal-sized gallbladder should be a mandatory component of the second-trimester anomaly ultrasound scan. Advances in prenatal sonography enable the detection of biliary tract congenital malformations. In this review, we discuss the detection rates, sonographic features, and prognosis of the most frequently prenatally diagnosed biliary tract malformations.

Digynic triploidy in a fetus presenting with semilobar holoprosencephaly

OBJECTIVE

We present digynic triploidy in a fetus with semilobar holoprosencephaly (HPE).

CASE REPORT

A 32-year-old, gravid 1, para 0, woman underwent prenatal ultrasound examination at 12 weeks of gestation, and the ultrasound showed relative macrocephaly, a small non-cystic placenta, and a fetus with absent nasal bone and semilobar HPE. The pregnancy was terminated subsequently, and a 50-g fetus was delivered with a relatively enlarged head and premaxillary agenesis. The placenta was small and non-cystic. Postnatal cytogenetic analysis of the umbilical cord revealed a karyotype of 69, XXX. Postnatal DNA marker analysis using quantitative fluorescent polymerase chain reaction assays and the polymorphic short tandem repeat markers for chromosome 18 and 20 on the placental tissues showed a diallelic pattern with a dosage of 1:2 (paternal allele to maternal allele ratio), indicating a maternal origin of the triploidy.

CONCLUSION

Fetuses with digynic triploidy may present relative macrocephaly, semilobar HPE and a small placenta on prenatal ultrasound.

A placenta clinic approach to the diagnosis and management of fetal growth restriction

Effective detection and management of fetal growth restriction is relevant to all obstetric care providers. Models of best practice to care for these patients and their families continue to evolve. Since much of the disease burden in fetal growth restriction originates in the placenta, the concept of a multidisciplinary placenta clinic program, managed primarily within a maternal-fetal medicine division, has gained popularity. In this context, fetal growth restriction is merely one of many placenta-related disorders that can benefit from an interdisciplinary approach, incorporating expertise from specialist perinatal ultrasound and magnetic resonance imaging, reproductive genetics, neonatal pediatrics, internal medicine subspecialties, perinatal pathology, and nursing. The accurate diagnosis and prognosis for women with fetal growth restriction is established by comprehensive clinical review and detailed sonographic evaluation of the fetus, combined with uterine artery Doppler and morphologic assessment of the placenta. Diagnostic accuracy for placenta-mediated fetal growth restriction may be enhanced by quantification of maternal serum biomarkers including placenta growth factor alone or combined with soluble fms-like tyrosine kinase-1. Uterine artery Doppler is typically abnormal in most instances of early-onset fetal growth restriction and is associated with coexistent preeclampsia and underlying maternal vascular malperfusion pathology of the placenta. By contrast, rare but potentially more serious underlying placental diagnoses, such as massive perivillous fibrinoid deposition, chronic histiocytic intervillositis, or fetal thrombotic vasculopathy, may be associated with normal uterine artery Doppler waveforms. Despite minor variations in placental size, shape, and cord insertion, placental function remains, largely normal in the general population. Consequently, morphologic assessment of the placenta is not currently incorporated into current screening programs for placental complications. However, placental ultrasound can be diagnostic in the context of fetal growth restriction, for example in Breus' mole and triploidy, which in turn may enhance diagnosis and management. Several examples are illustrated in our figures and supplementary videos. Recent advances in the ability of multiparameter screening and intervention programs to reduce the risk of severe preeclampsia will likely increase efforts to deliver similar improvements for women at risk of fetal growth restriction. Placental pathology is important because the underlying pathologies associated with fetal growth restriction have a wide range of recurrence risks. Rare conditions such as massive perivillous fibrinoid deposition or chronic histolytic intervillositis may recur in >50% of subsequent pregnancies. Postpartum care in a placenta-focused program can provide effective counseling for modifiable maternal risk factors, and can assist in planning future pregnancy care based on the pathologic basis of fetal growth restriction.