Contribution of amniocentesis in fetuses small for gestational age without other sonographic signs

OBJECTIVE

Our study evaluated the contribution of amniocentesis in the diagnostic approach of small-for-gestational-age fetuses (SGA) without morphological abnormality identified on ultrasound by studying FISH (fluorescence in situ hybridization) for chromosomes 13, 18 and 21, CMV PCR (cytomegalovirus polymerase chain reaction), karyotype and CGH (genomic hybridization array) METHODS: Our single-center retrospective cohort study included pregnant women referred for prenatal diagnosis for a SGA fetus in whom amniocentesis was performed between 2016 and 2019. A SGA fetus was defined as a fetus with an estimated fetal weight (EFW) below the 10th percentile according to referral growth curves in use. We evaluated the number of amniocenteses with an abnormal result and identified factors that may be associated with this outcome.

RESULTS

Among the 79 amniocenteses performed, there were 5 (6.3%) abnormalities: karyotype (1.3%) and CGH (5.1%). No complications were described. We did not find any statistically significant factors associated with abnormal amniocentesis findings even if some elements seemed reassuring such as late discovery (p = 0.31), moderate SGA (p = 0.18), normal head, abdomen and femur measurements (p = 0.57), but without statistically significant difference.

CONCLUSION

Our study found 6.3% pathological analysis of amniocenteses, of which several would have been missed by conventional karyotyping. Patients must be informed about the risk of detecting abnormalities of low severity, with low penetrance or with unknown fetal consequences that could be source of anxiety.

Exome sequencing in fetuses with short long bones detected by ultrasonography: A retrospective cohort study

Background: Prenatal diagnosis of fetal short long bones (SLBs) was reported to be associated with skeletal dysplasias, chromosomal abnormalities, and genetic syndromes. This study aims to identify the genetic causes for fetal short long bones, and retrospectively evaluate the additional diagnostic yield of exome sequencing (ES) for short long bones following the use of conventional genetic testing. Methods: A cohort of ninety-four fetuses with sonographically identified short long bones was analyzed by trio-exome sequencing between January 2016 and June 2021. Fetuses with abnormal results of karyotype or chromosomal microarray analysis were excluded. Variants were interpreted based on ACMG/AMP guidelines. All diagnostic de novo variants were validated by Sanger sequencing. Results: Of the 94 fetuses, 38 (40.4%) were found to carry causal genetic variants (pathogenic or likely pathogenic) in sixteen genes with 38 variants. Five fetuses (5.3%) had variant(s) of uncertain significance. Thirty-five cases (37.2%) were diagnosed as genetic skeletal dysplasias including 14 different diseases that were classified into 10 groups according to the Nosology and Classification of Genetic Skeletal Disorders. The most common disease in the cohort was achondroplasia (28.9%), followed by osteogenesis imperfecta (18.4%), thanatophoric dysplasia (10.5%), chondrogenesis (7.9%), and 3-M syndrome (5.3%). The diagnostic yield in fetuses with isolated short long bones was lower than the fetuses with non-isolated short long bones, but not reached statistical significance (27.3% vs. 44.4%; p = 0.151). Whereas, the rate in the fetuses with other skeletal abnormalities was significantly higher than those with non-skeletal abnormalities (59.4% vs. 32.5%, p = 0.023), and the diagnostic rate was significantly higher in femur length (FL) below -4SDs group compared with FL 2-4SDs below GA group (72.5% vs. 16.7%; p < 0.001). A long-term follow-up showed that outcomes for fetuses with FL 2-4SDs below GA were significantly better than those with FL below -4SDs. Additionally, fourteen (36.8%) novel short long bones-related variants were identified in the present study. Conclusion: The findings suggest that in fetuses with short long bones routine genetic tests failed to determine the underlying causes, exome sequencing could add clinically relevant information that could assist the clinical management of pregnancies. Novel pathogenic variants identified may broaden the mutation spectrum for the disorders and contributes to clinical consultation and subsequent pregnancy examination.