Ultrasound screening for fetal chromosome anomalies

Pathogenic copy number variations are associated with foetal short femur length in a tertiary referral centre study

Shortened foetal femur length (FL) is a common abnormal phenotype that often causes anxiety in pregnant women, and standard clinical treatments remain unavailable. We investigated the clinical characteristics, genetic aetiology and obstetric pregnancy outcomes of foetuses with short FL and provided a reference for perinatal management of such cases. Chromosomal microarray analysis was used to analyse the copy number variations (CNV) in short FL foetuses. Of the 218 foetuses with short FL, 33 foetuses exhibited abnormal CNVs, including 19 with pathogenic CNVs and 14 with variations of uncertain clinical significance. Of the 19 foetuses with pathogenic CNVs, four had aneuploidy, 14 had deletions/duplications, and one had pathogenic uniparental diploidy. The 7q11.23 microdeletion was detected in three foetuses. The severity of short FL was not associated with the rate of pathogenic CNVs. The duration of short FL for the intrauterine ultrasound phenotype in foetuses carrying a pathogenic CNV was independent of the gestational age. Further, maternal age was not associated with the incidence of foetal pathogenic CNVs. Adverse pregnancy outcomes occurred in 77 cases, including termination of pregnancy in 63 cases, postnatal dwarfed foetuses with intellectual disability in 11 cases, and three deaths within 3 months of birth. Pathogenic CNVs closely related to foetal short FL were identified, among which the 7q11.23 microdeletion was highly associated with short FL development. This study provides a reference for the perinatal management of foetuses with short FL.

Microarray-based prenatal diagnosis for the identification of fetal chromosome abnormalities

The goal of prenatal cytogenetic testing is to provide reassurance to the couple seeking testing for their pregnancy, identify chromosome abnormalities in the fetus, if present, and provide treatments and medical management for affected babies. Cytogenetic analysis of banded chromosomes has been the standard for identifying chromosome abnormalities in the fetus for over 40 years. With chromosome analysis, whole chromosome aneuploidies and large structural rearrangements can be identified. The sequencing of the human genome has provided the resources to develop molecular tools that allow higher resolution observations of human chromosomes. The future holds the promise of sequencing that may identify chromosomal imbalances and deleterious single nucleotide variants. This review will focus on the use of genomic microarrays for the testing and identification of chromosome anomalies in prenatal diagnosis and will discuss the future directions of fetal testing.

Detection rates of clinically significant genomic alterations by microarray analysis for specific anomalies detected by ultrasound

OBJECTIVE

The aim of this study is to understand the diagnostic utility of comparative genomic hybridization (CGH)-based microarrays for pregnancies with abnormal ultrasound findings.

METHODS

We performed a retrospective analysis of 2858 pregnancies with abnormal ultrasounds and normal karyotypes (when performed) tested in our laboratory using CGH microarrays targeted to known chromosomal syndromes with later versions providing backbone coverage of the entire genome. Abnormalities were stratified according to organ system involvement. Detection rates for clinically significant findings among these categories were calculated.

RESULTS

Clinically significant genomic alterations were identified in cases with a single ultrasound anomaly (n = 99/1773, 5.6%), anomalies in two or more organ systems (n = 77/808, 9.5%), isolated growth abnormalities (n = 2/76, 2.6%), and soft markers (n = 2/77, 2.6%). The following anomalies in isolation or with additional anomalies had particularly high detection rates: holoprosencephaly (n = 9/85, 10.6%), posterior fossa defects (n = 21/144, 14.6%), skeletal anomalies (n = 15/140, 10.7%), ventricular septal defect (n = 14/132, 10.6%), hypoplastic left heart (n = 11/68, 16.2%), and cleft lip/palate (n = 14/136, 10.3%).

CONCLUSIONS

Microarray analysis identified clinically significant genomic alterations in 6.5% of cases with one or more abnormal ultrasound findings; the majority were below the resolution of karyotyping. Larger data sets such as this allow for sub-stratification by specific anomalies to determine risks for genomic alterations detectable by microarray analysis.

Uptake of invasive prenatal diagnostic tests in women after detection of soft markers for chromosomal abnormality on ultrasonographic evaluation

OBJECTIVE

Use of soft ultrasonographic markers during routine prenatal ultrasonography (USG) may be used for the screening of aneuploidy in the low-risk population. The aim of this study was to evaluate the acceptance of an invasive test for prenatal diagnosis and to assess the role of various factors in the decision-making regarding an invasive test when confronted with risk for aneuploidy after a soft marker is detected on routine antenatal ultrasonogram.

STUDY DESIGN

Women were referred for USG in our department by primary obstetricians for indications such as a previous child with a congenital malformation, genetic disorder, stillbirth or in women with recurrent spontaneous abortions. Some of the women were referred after prenatal detection of a soft marker on USG. They were screened for soft markers associated with chromosomal abnormality. They were counseled regarding the age-specific risk and the risk of aneuploidy after detection of a marker in comparison to the general population's risk of Down's syndrome. They were also counseled regarding the risk of a procedure-related abortion (0.5%) following an invasive procedure before their decision regarding the use of amniocentesis was made.

RESULT

Twenty women out of 50 (40%) opted for amniocentesis. Except in one case of trisomy 21 in a fetus with short femur and humerus, all others had normal karyotype. The uptake of the test was comparable between primigravida (33%), women with poor obstetric history (46%) and women with at least one normal live child (45%). There was no statistical difference in the uptake of invasive test based on gestational age as well. Uptake of amniocentesis was higher (78%) in cases with nuchal thickening as compared to other markers (35%).

CONCLUSION

Ultrasonographic detection of soft markers is associated with a high frequency of uptake for invasive prenatal testing. Increased nuchal thickening is associated with a higher acceptance of amniocentesis. Maternal age, gestational age or previous obstetric history were not associated with the decision to undergo amniocentesis.

Contribution of ultrasonographic examination to the prenatal detection of trisomy 21: experience from 19 European registers

The objective of this study was to evaluate the contribution of ultrasound scanning to the prenatal detection of trisomy 21 in a large unselected European population. Data from 19 congenital malformation registers in 11 European countries were included. The prenatal ultrasound screening programs in the countries ranged from no routine screening to three ultrasound investigations per patient. Routine serum screening was offered in four of the 11 countries and routine screening on the basis of maternal age amniocentesis in all. The results show that overall 53% of cases of trisomy 21 were detected prenatally with a range from 3% in Lithuania to 88% in Paris. Ninety-eight percent of women whose babies were diagnosed before 24 weeks gestation chose to terminate the pregnancy. Centres/countries that offer serum screening do not have a significantly higher detection rate of trisomy 21 when compared to those that offer maternal age amniocentesis and anomaly scanning only. Fifty percent of trisomy 21 cases were born to women aged 35 years or more. In conclusions, second trimester ultrasound plays an important role in the prenatal diagnosis of trisomy 21. Of those cases prenatally diagnosed, 64% of cases in women <35 years and 36% of those in women >or=35 years were detected because of an ultrasound finding. Ultrasound soft markers accounted for 84% of the scan diagnoses. There is evidence of increasing maternal age across Europe with 50% of cases of trisomy 21 born to women aged 35 years or more.

An ethnic predilection for fetal echogenic intracardiac focus identified during targeted midtrimester ultrasound examination: A retrospective review

BACKGROUND: Echogenic intracardiac focus (EIF) has been identified as a common ultrasound finding in association with fetal aneuploidy. Little is known about the association of this soft marker aneuploidy in various ethnic groups. Although it is commonly thought Asians in general have a higher incidence of EIF, it is unknown whether this also applies to Japanese as a subpopulation. The purpose of this study is to determine the antenatal incidence and postnatal significance of EIF observed during sonography in Japanese patients. METHODS: A cohort of Japanese patients who underwent ultrasound screening from 1997 to 1999 in the ultrasound unit at the New York University School of Medicine was identified. Variables included age, gestational age, serum markers, and the presence or absence of aneuploidy. Patients with first degree paternal or maternal Japanese ancestry were included for analysis. Examinations were performed between 14 and 24 weeks gestation. The prevalence of EIF was calculated. The control group was based on previously published data in the U.S (7.3% prevalence). RESULTS: A total of 154 subjects were identified, 148 were available for final analysis. Twenty-two fetuses had an EIF, 19 (86.4%) left-sided, 3 (13.6%) right-sided. Seventeen patients had other sonographic markers associated with aneuploidy. The mean maternal age at diagnosis was 30.7 +/- 3.9 years and the mean gestational age was 19.8 +/- 1.6 weeks. The prevalence of EIF was 14.8%. Compared to published population prevalence, there was a statistically significant difference (p < 0.005). No abnormal karyotypes were found. CONCLUSION: Asians of Japanese origin may have a higher prevalence of echogenic intracardiac foci, thus affecting the positive predictive value of this sonographic marker for aneuploidy.

Demographic and prenatal factors of patients with cleft lip and cleft palate

BACKGROUND

Cleft lip, or CL, and cleft palate, or CP, are common congenital abnormalities. Birth prevalence ranges from one in every 500 to 1,000 in the white population and one in every 2,000 births in the African-American population. Etiologic and genetic factors contributing to CL and CP development are unknown though extensive research has been conducted. The authors conducted this pilot study to investigate a study design that could allow for an evaluation of such etiologic factors by providing the required estimate of the projected magnitude of differences between cases and controls.

METHODS

The authors obtained pregnancy history data from the mothers of 137 consecutive patients at the University of Pittsburgh Cleft Palate-Craniofacial Center. The authors investigated the differences between sex or cleft status and family history of clefts, birth order, maternal age at birth and first-trimester maternal smoking and alcohol consumption.

RESULTS

None of the factors showed any significant differences by sex or cleft type (P > or = .07) in the pilot data. Power estimates ranged from 12 to 71 percent. The sample size needed to obtain power of 80 percent would be 250 for variables with two categories and 480 for variables with three categories.

CONCLUSIONS

There is no evidence that the factors contribute to either sex or cleft status differences. Further investigations are needed, and they should include a larger, more diverse sample of at least 250 cases, a matched control group and a focus on mothers of newborns.

CLINICAL IMPLICATIONS

This study lays the groundwork for a better understanding of the etiology of CL and CP-common birth defects that present challenges for long-term dental management.

Use of genetic sonography for adjusting the risk for fetal Down syndrome

Systematic evaluation of ultrasound findings known to be associated with trisomy 21, at an appropriate gestational age, has been referred to as a genetic sonogram. A number of high-risk centers performing genetic sonography have reported detection of ultrasound abnormalities in the majority of fetuses with fetal Down syndrome. However, nonspecific markers are more commonly observed than structural abnormalities, which are detected in less than 20% of cases in a nonselected population. Also, the actual sensitivity of a genetic sonogram will depend on various factors including the markers sought, gestational age, reasons for referral, and of course the quality of the ultrasound. Appropriate use of a genetic sonogram can help to modify the risk of fetal Down syndrome by decreasing the risk when the ultrasound is normal, or increasing the risk when specific ultrasound markers are detected. The postultrasound risk can be estimated by applying specific likelihood ratios, reflecting the strength of individual markers, with the a priori risk based on maternal age alone, or combined with biochemical markers when known. We review this approach of age-adjusted ultrasound risk assessment for fetal Down syndrome and illustrate how the risk can be estimated. Individual sonographic markers are also discussed.

Advances in prenatal screening for Down syndrome: I. general principles and second trimester testing

BACKGROUND

Down syndrome is one of the most important causes of mental retardation in the population. In the absence of prenatal screening and diagnosis, prevalence at birth in the United States would currently exceed 1:600. The purpose of prenatal screening is to identify those women at the increased risk for an affected pregnancy and to maximize the options available to these women.

TESTS AVAILABLE

Second trimester serum screening involves combining the maternal age-specific risk for an affected pregnancy with the risks associated with the concentrations of maternal serum alpha-fetoprotein (MSAFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) (triple testing). A forth analyte, inhibin-A (INH-A), is increasingly being utilized (quadruple testing). Optimal second trimester screening requires the integration of a number of clinical variables, the most important of which is an accurate assessment of gestational age. In addition to Down syndrome, the triple and quadruple tests preferentially identify fetal trisomy 18, Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith-Lemli-Opitz syndrome, and steroid sulfatase deficiency. Some programs modify the Down syndrome risks generated through maternal serum screening tests with fetal biometric data obtained by ultrasound. Other second trimester tests have shown promise, including the analysis of maternal urine and fetal cells in the maternal circulation, but none are in routine clinical use.

CONCLUSION

The second trimester triple and quadruple tests provide benchmarks for evaluating new screening protocols. The combination of fetal biometry, new test development as well as clarification of the role of co-factors that affect the concentrations of analytes in existing tests should lead to greater efficacy in second trimester screening for Down syndrome.

Sonographic nuchal markers for Down syndrome are more common but less ominous in gestations with a male fetus

OBJECTIVE

A change in the normal male-to-female ratio has been reported in some autosomal trisomies (i.e., trisomy 21 or trisomy 18). The objective of the present study was to evaluate the male-to-female ratio in pregnancies with sonographic nuchal markers for Down syndrome.

METHODS

The results of amniocenteses performed for isolated nuchal markers for Down syndrome were grouped by fetal sex and by maternal age. The male-to-female ratio in normal and trisomic gestations was compared.

RESULTS

584 fetal karyotypes were available for analysis. A significantly higher male-to-female ratio was observed. More affected gestations were observed in association with a female fetus. These differences were mainly attributed to the group of patients younger than 35 years that represents more than 80% of our study population. No difference was observed in pregnancies of patients older than 35 years of age.

CONCLUSIONS

In patients younger than 35 years, sonographic nuchal markers for Down syndrome are more frequent (but apparently less ominous) in gestations with a male fetus. If the gender is known, counseling can be modified to include such differential risks.

Prenatal diagnosis of de novo distal 11q deletion associated with sonographic findings of unilateral duplex renal system, pyelectasis and orofacial clefts

In utero diagnosis of de novo distal 11q deletion associated with renal and orofacial malformations has not been previously described. We present a 35-year-old pregnant woman with prenatal sonographic findings of a unilateral duplex renal system, pyelectasis and orofacial clefts at 20 weeks' gestation. Both genetic amniocentesis and postnatal cytogenetic analysis revealed de novo 46,XX,del(11)(q23). After birth, the fetus manifested a dysmorphic phenotype correlated with del(11q) syndrome. Genetic marker analysis showed a paternally derived distal deletion of chromosome 11q and a breakpoint centromeric to D11S1341. The present case represents the earliest prenatal diagnosis of a duplex renal system, pyelectasis and an additional feature of orofacial clefts associated with distal 11q deletion. Prenatal sonographic detection of a duplex renal system, pyelectasis and orofacial clefts should warrant a careful assessment of fetal anatomy and prompt cytogenetic analysis looking for chromosomal aberrations.

Genetic counselling in prenatally diagnosed non-chromosomal fetal abnormalities

Advances in technology and skills have resulted in the improved detection of fetal ultrasound abnormalities by ultrasound. In addition, the development of new diagnostic methods has resulted in major advances in our ability to detect microscopic and submicroscopic chromosome abnormalities as well as single gene disorders. This often enables us to provide the family with accurate information regarding the aetiology, prognosis, the risk of recurrence and the prenatal diagnosis options available in future pregnancies. Genetic counselling is important because this information should be communicated to the family in simple language, with care and sensitivity, so that the family can make decisions that are fully informed.