2017 Update on obstetrics

Chromosomal microarray analysis is preferable to karyotype in certain situations  

Pauli JM, Repke JT. Update on obstetrics. OBG Manag. 2013;25(1):28-32.

Society for Maternal-Fetal Medicine (SMFM), Dugoff L, Norton ME, Kuller JA. The use of chromosomal microarray for prenatal diagnosis. Am J Obstet Gynecol. 2016;215(4):B2-B9.

American College of Obstetricians and Gynecologists. Committee Opinion No. 682. Microarrays and next- generation sequencing technology: the use of advanced genetic diagnostic tools in obstetrics and gynecology.Obstet  Gynecol. 2016;128(6):e262-e268.

We previously addressed the use of chromosomal microarray analysis (CMA) for prenatal diagnosis in our 2013 "Update on obstetrics," specifically, the question of whether CMA could replace karyotype. The main differences between karyotype and CMA are that 1) only karyotype can detect balanced translocations/inversions and 2) only CMA can detect copy number variants (CNV). There are some differences in the technology and capabilities of the 2 types of CMA currently available as well.

In our 2013 article we concluded that "The total costs of such an approach--test, interpretation, counseling, and long-term follow-up of uncertain results--are unknown at this time and may prove to be unaffordable on a population-wide basis." Today, the cost of CMA is still higher than karyotype, but it is expected to decrease and insurance coverage for this test is expected to increase.

Related article:
Cell-free DNA screening for women at low risk for fetal aneuploidy

Both SMFM and ACOG released recommendations in 2016 regarding the use of CMA in prenatal genetic diagnosis, summarized as follows:  

• CMA is recommended over karyotype for fetuses with structural abnormalities on ultrasound
  • The detection rate for clinically relevant abnormal CNVs in this population is about 6%
• CMA is recommended for diagnosis for stillbirth specimens
  • CMA does not require dividing cells and may be a quicker and more reliable test in this population
• Karotype or fluorescence in situ hybridization (FISH) is recommended for fetuses with ultrasound findings suggestive of aneuploidy
  • If it is negative, then CMA is recommended
• Karyotype or CMA is recommended for patients desiring prenatal diagnostic testing with a normal fetal ultrasound
  • The detection rate for clinically relevant CNVs in this population (advanced maternal age, abnormal serum screening, prior aneuploidy, parental anxiety) is about 1%
• Pretest and posttest counseling about the limitations of CMA and a 2% risk of detection of variants of unknown significance (VUS) should be performed by a provider who has expertise in CMA and who has access to databases with genotype/phenotype information for VUS
  • This counseling should also include the possibility of diagnosis of nonpaternity, consanguinity, and adult-onset disease
• Karyotype is recommended for couples with recurrent pregnancy loss
  • The identification of balanced translocations in this population is most relevant in this patient population
• Prenatal diagnosis with routine use of whole-genome or whole-exome sequencing is not recommended.

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