Ultrasound diagnosis of fetal abnormalities and cytogenetic evaluation

Fetal central nervous system anomalies: When should we offer exome sequencing?

OBJECTIVE

To investigate the detection of pathogenic variants using exome sequencing in an international cohort of fetuses with central nervous system (CNS) anomalies.

METHODS

We reviewed trio exome sequencing (ES) results for two previously reported unselected cohorts (Prenatal Assessment of Genomes and Exomes (PAGE) and CUIMC) to identify fetuses with CNS anomalies with unremarkable karyotypes and chromosomal microarrays. Variants were classified according to ACMG guidelines and association of pathogenic variants with specific types of CNS anomalies explored.

RESULTS

ES was performed in 268 pregnancies with a CNS anomaly identified using prenatal ultrasound . Of those with an isolated, single, CNS anomaly, 7/97 (7.2%) had a likely pathogenic/pathogenic (LP/P) variant. This includes 3/23 (13%) fetuses with isolated mild ventriculomegaly and 3/10 (30%) fetuses with isolated agenesis of the corpus callosum. Where there were multiple anomalies within the CNS, 12/63 (19%) had LP/P variants. Of the 108 cases with CNS and other organ system anomalies, 18 (16.7%) had LP/P findings.

CONCLUSION

ES is an important tool in the prenatal evaluation of fetuses with any CNS anomaly. The rate of LP/P variants tends to be highest in fetuses with multiple CNS anomalies and multisystem anomalies, however, ES may also be of benefit for isolated CNS anomalies.

Spectrum of Chromosomal Abnormalities Detected by Conventional Cytogenetic Analysis Following Invasive Prenatal Testing of Fetuses with Abnormal Ultrasound Scans

Objectives

The frequent association between malformations and chromosomal abnormalities is now well-established. This study looks at the incidence and type of chromosomal abnormalities detected by conventional cytogenetic analysis in women undergoing invasive tests following detection of fetal anomalies on antenatal scans as well as incidence of other genetic abnormalities detected by DNA analysis of fetuses with congenital anomalies that had a normal karyotype.

Materials and Methods

A retrospective, observational study of pregnant women undergoing invasive testing following identification of fetal anomalies by ultrasonography was carried out in a tertiary care facility, Vellore, India, between 2011 and 2018.

Results

169 women underwent an invasive diagnostic procedure following detection of fetal anomalies. The most common indication for doing fetal karyotype was the presence of major fetal structural anomalies (142/169, 84%) with over a third (48/142, 34%) having multisystem involvement. Fetal hydrops was the next most common indication, detected in 18/169 (10%) fetuses. Aneuploidy was seen 19 of 25 fetuses (76%) with an abnormal karyotype with autosomal aneuploidy accounting for 13 (68%) and sex chromosome aneuploidy for seven (37%) of the fetuses. One fetus had double aneuploidy. In fetuses with normal karyotype, no additional information was obtained from further genetic testing.

Conclusions

The overall detection rate of chromosomal abnormalities in our study using conventional cytogenetic analysis was 14.8%, the majority (72%) being associated with structural malformations, 20% with non-immune hydrops and 4% with soft markers. Abnormal karyotypes were seen in 12.7% of fetuses with structural malformations.

Chromosomal aberrations in idiopathic polyhydramnios: A systematic review and meta-analysis

The objective of this meta-analysis was to summarize the existing literature examining the risk of chromosomal aberrations in idiopathic polyhydramnios. Search was conducted by a research librarian in five databases. Language and time restrictions were not applied. By independent screening of titles and abstracts, two investigators selected original researches examining the risk of chromosomal aberrations in idiopathic polyhydramnios. Twenty articles were included, encompassing a total of 1729 pregnancies with idiopathic polyhydramnios. The average rate of chromosomal aberrations in these cases was 2.8 ± 3.7%, ranging between 0% and 13.8%. No studies were found examining the relative risk for chromosomal abnormalities in low-risk women with idiopathic polyhydramnios. An analysis of seven case-control trials, including women at high risk for aneuploidy, yielded a relative risk of 3.09 (95% confidence interval 1.92-4.97) for chromosomal aberration. Overall quality of evidence was rated as very low using Grading of Recommendations Assessment, Development and Evaluation criteria. In conclusion, the suboptimal quality of the evidence precludes from drawing any solid recommendations regarding routine karyotype testing in idiopathic polyhydramnios cases, especially in women at low risk for chromosomal aberrations. Future high-quality trials addressing the discussed methodological shortcomings should be conducted to assess this important issue.

Additional value of prenatal genomic array testing in fetuses with isolated structural ultrasound abnormalities and a normal karyotype: a systematic review of the literature

OBJECTIVE

To establish the prevalence of submicroscopic genetic copy number variants (CNVs) in fetuses with a structural ultrasound anomaly (restricted to one anatomical system) and a normal karyotype. The aim was to determine the diagnostic and prognostic value of genomic array testing in these pregnancies.

METHODS

Embase and PubMed databases were systematically searched for all relevant articles on prevalence of pathogenic submicroscopic CNVs in fetuses with ultrasound anomalies. Reported cases were sorted into groups according to anatomical site of the detected ultrasound anomaly. The prevalence of causative submicroscopic CNVs was calculated for each group.

RESULTS

Combined data of the reviewed studies (n = 18) indicated that fetuses with an ultrasound anomaly restricted to one anatomical system (n = 2220) had a 3.1-7.9% chance of carrying a causative submicroscopic CNV, depending on the anatomical system affected. This chance increased to 9.1% for fetuses with multiple ultrasound anomalies (n = 1139).

CONCLUSION

This review indicates that 3.1-7.9% of fetuses with a structural ultrasound anomaly restricted to one anatomical system and a normal karyotype will show a submicroscopic CNV, which explains its phenotype and provides information for fetal prognosis. Therefore, we conclude that microarray has considerable diagnostic and prognostic value in these pregnancies.

Outcome of fetal exomphalos diagnosed at 11-14 weeks of gestation

OBJECTIVE

To determine whether sonographic findings in cases of exomphalos detected at the 11-14-week scan can be used to guide pregnancy management.

METHODS

Retrospective study of cases of exomphalos identified from the Fetal Medicine Unit database, University College London Hospitals between January 1998 and January 2010. Pregnancy and neonatal data were ascertained from maternal and neonatal records. Fetal exomphalos was categorized into three groups: exomphalos associated with other major structural malformation(s), isolated exomphalos with increased nuchal translucency (NT) and isolated exomphalos with normal NT.

RESULTS

A total of 98 cases of exomphalos were identified, of which 45 (45.9%) were associated with other major structural malformation(s), identified antenatally. Isolated exomphalos was found with increased NT in 22 cases (22.4%) and with normal NT in 31 cases (31.6%). Of 80 (81.6%) fetuses that were karyotyped, 43 (53.8%) had a chromosomal abnormality; the most common aneuploidy was trisomy 18 (n = 31; 72.1%). Where exomphalos was associated with other major structural abnormalities, or was isolated with increased NT, the incidence of aneuploidy was high, at 78.9% and 72.2%, respectively. Cases of isolated exomphalos with normal NT were all euploid. In 21 cases (21.4%), exomphalos resolved later in pregnancy and none had apparent abnormalities at birth; isolated exomphalos persisted in only three neonates (3.1%).

CONCLUSIONS

The finding of a major structural abnormality or of increased NT in association with exomphalos in the first trimester implies a high risk of aneuploidy. Parents can be reassured that fetuses with isolated exomphalos and normal NT are likely to be euploid.

Should determination of the karyotype be systematic for all malformations detected by obstetrical ultrasound?

OBJECTIVE

The aim of this study was to determine whether karyotyping should be performed for every fetal malformation detected in low risk populations.

METHODS

A karyotype was obtained from 428 fetuses examined over a 10-year period after fetal malformation was diagnosed using obstetrical ultrasound. These fetuses were separated into two groups, one with isolated malformations and the other with multiple malformations. The association between each type of malformation and the result of karyotype was evaluated.

RESULTS

Forty-eight chromosomal abnormalities were encountered in 428 fetuses (11.2%). The karyotype was abnormal in 32/343 (9.3%) fetuses with isolated malformations and 16/85 (18.8%) fetuses with multiple malformations (p=0.022). The probability of an abnormal karyotype among the group of isolated malformation depended on the anatomical system involved (p<0.001). Our study demonstrated several isolated malformations without chromosomal abnormality (hydronephrosis with high obstruction, unilateral multicystic dysplastic kidney, gastroschisis, intestinal dilatation, meconium peritonitis, cystic adenomatoid malformation, pulmonary sequestration, tumor, vertebral anomaly).

CONCLUSION

Each fetus with multiple malformations needs a chromosomal analysis. Within the group of isolated malformations, our study emphasizes that medical maternal history and the type of malformation need to be taken into account before performing a fetal karyotype.

Omphalocele in Miller-Dieker syndrome: expanding the phenotype

We report on a patient prenatally diagnosed with omphalocele, mild cerebral ventriculomegaly, nuchal fold thickening, and cystic changes in the umbilical cord who was found postnatally to have lissencephaly type I. Prenatal chromosome analysis showed a normal male karyotype; however, postnatal high resolution banding and FISH analysis, using a probe for locus D17S379 in chromosome region 17p13.3, demonstrated a deletion at 17p13.3 consistent with Miller-Dieker syndrome (MDS). A review documented four more cases with MDS/isolated lissencephaly/17p-, with omphalocele. Because MDS is a contiguous gene disorder, we speculate that a gene or genes in this region have a major role in the closure of the lateral folds or the return of the midgut from the body stalk to the abdomen at 5-11 weeks of gestation. Prenatal diagnosis of omphalocele with mild ventriculomegaly should prompt FISH analysis for a deletion in 17p13.3.

Distribution of abnormal karyotypes among malformed fetuses detected by ultrasound throughout gestation

A karyotype was obtained from 755 fetuses with structural anomalies detected by sonography between 13 and 40 weeks' gestation. Gestational age was found to have no influence on the prevalence of chromosomal aberrations. The incidence in the second and third trimesters of pregnancy was 15.7 and 17.5 per cent, respectively. The contribution of the different malformations to such proportions did, however, change throughout gestation. Cystic hygroma was by far predominant in the early second trimester, cardiac defects in the late second trimester, and duodenal atresia in late pregnancy. Our findings confirm that karyotyping of malformed fetuses is highly advisable; the importance of chromosomal investigation is not dependent on the gestational age at detection of the structural defect as the likelihood of finding a chromosomal anomaly during the second and third trimesters is quite similar. Spontaneous intrauterine selection of chromosomally abnormal fetuses is most likely counterbalanced by the limited accuracy of prenatal ultrasound in recognizing many fetal anomalies early in pregnancy.

The natural history of euploid pregnancies with first-trimester cystic hygromas

OBJECTIVES

Little information is available with regard to prognosis of euploid fetuses with first-trimester nuchal hygromas. To evaluate this population, the natural history, pregnancy outcome, and pediatric implication of this lesion were determined.

STUDY DESIGN

Fetuses with cystic hygromas detected in the first trimester were retrospectively identified, and karyotype results were documented. Pregnancy outcome of those fetuses having a euploid karyotype was obtained, and physical examination of the live-born neonates and infants was performed by a clinical geneticist.

RESULTS

A normal karyotype was identified in 22 (51%) of these pregnancies. Eighty-two percent of the euploid pregnancies were continued, with 89% of the fetuses surviving to the third trimester. Dysmorphic sequelae were documented in three children, including Noonan syndrome in one.

CONCLUSION

In the presence of a normal karyotype fetuses with a first-trimester nuchal hygroma have an excellent prognosis. Normal outcome was seen in 80% of pregnancies carried to the third trimester.

Room for improvement? Detecting autosomal trisomies without serum screening

OBJECTIVE

To assess the efficacy of the prenatal screening and diagnostic programme for the detection of the common autosomal trisomies in the North West Thames region prior to the introduction of serum screening.

DESIGN

A retrospective study based on reports made to the North West Thames Regional Health Authority Congenital Malformation Register.

SUBJECTS

235 pregnancies of women delivered in units in the North West Thames region over a two-year period (1990-91) whose babies or fetuses were diagnosed as having Down, Edwards or Patau syndrome.

RESULTS

33% of Down syndrome, 68% of Edwards syndrome and 52% of Patau syndrome were diagnosed prenatally (before 28 weeks) in the region without the use of serum screening.

CONCLUSIONS

Using maternal age and routine ultrasound as screening methods, units in the region are prenatally diagnosing significantly fewer Down syndrome babies than are those in authorities using serum screening. The use of maternal age and ultrasound screening is more effective for the antenatal detection of the other autosomal trisomies than it is for the detection of Down syndrome. It is not yet clear to what extent serum screening might be expected to increase the detection rate for these conditions.

Chromosomal abnormalities associated with a single umbilical artery

A single umbilical artery was seen in 10 out of 117 cytogenetically abnormal pregnancies. The abnormal karyotypes found to be associated with a single umbilical artery were trisomy 18 (n = 5), monosomy X (n = 2), triploidy (n = 1), sex chromosome (47,XYY; n = 1) and translocation (46t(X,5)(q13p15);n = 1). With the exception of the translocation case, all cases with a single umbilical artery had anatomical defects which were detectable ultrasonographically. This suggests that a single umbilical artery alone is not an indication for prenatal fetal karyotyping.

First-trimester diagnosis of cystic hygroma--course and outcome

OBJECTIVE

We studied the outcomes of fetuses in whom cystic hygroma was diagnosed in the first trimester of pregnancy through the application of transvaginal ultrasonography.

STUDY DESIGN

In the period 1990 to 1991 22 fetuses with cystic hygroma were found. All fetuses had karyotyping and a complete ultrasonographic search for associated anomalies.

RESULTS

Aneuploidy was found in seven of 22 fetuses: four trisomy 21, two trisomy 18, and one translocation. Monosomy X was absent in this series. In 15 of 22 cases there was a normal karyotype. In 10 of 15 euploid fetuses the small nonseptated hygroma resolved spontaneously. In four of 15 euploid fetuses other malformations were detected with ultrasonography (i.e., polycystic kidneys, coarctation of the aorta, bladder outlet obstruction, and fetal hydrops).

CONCLUSION

Whenever a cystic hygroma is suspected in the antenatal period, even if of small size, a structured and detailed ultrasonographic examination and fetal karyotyping are recommended.