Clinical Review

UPDATE ON OBSTETRICS

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The drive to do more and do it faster continues, leading to notable advances in prenatal diagnosis and fetal therapy, but is not sustainable over the long term


 

References

The authors report no financial relationships relevant to this article.

If there have been overriding themes in obstetrics over the past year, they have been “more,” “sooner,” “faster,” “safer.” Advances in our field have thrilled our scientific curiosity and increased our ability to alleviate suffering—but at what cost? And who will pay that cost?

In this Update, we focus on recent advances in prenatal diagnosis and fetal therapy, as well as the ever-encroaching economic barriers that may limit our ability to get what we want. In particular, we will discuss:

  • two technologies in prenatal genetics: noninvasive aneuploidy testing using cell-free DNA and prenatal microarray analysis
  • open fetal surgery to reduce mortality and improve the function and quality of life for fetuses with open neural tube defects
  • the value and probable impact of bundled payments—that is, one payment for multiple services grouped into one “episode.”

Two noninvasive approaches to prenatal diagnosis offer promise—but practicality and cost are uncertain

Ashoor G, Syngelaki RM, Wagner M, Birdir C, Nicolaides KH. Chromosome-selective sequencing of maternal plasma cell-free DNA for first-trimester detection of trisomy 21 and trisomy 18. Am J Obstet Gynecol. 2012;206(4):322.e1–e5.

Reddy UM, Page GP, Saade GR, et al. Karyotype versus microarray testing for genetic abnormalities after stillbirth. N Engl J Med. 2012;367(23):2185–2193.

Talkowski ME, Ordulu Z, Pillalamarri V, et al. Clinical diagnosis by whole-genome sequencing of a prenatal sample. N Engl J Med. 2012;367(23):2226–2232.

Wapner RJ, Martin CL, Levy B, et al. Chromosomal microarray versus karyotyping for prenatal diagnosis. N Engl J Med. 2012;367(23):2175–2184.

Genetic screening and testing are a standard part of prenatal care in most developed countries. We have come a long way since a maternal age of 35 years was the only variable separating patients into low- and high-risk categories. This year, two technologies have emerged that may change forever the way we approach prenatal genetics:

  • noninvasive aneuploidy testing using cell-free DNA
  • prenatal microarray analysis.14

One argument for using more accurate genetic screening methods: They limit the number of invasive tests that are needed. Chorionic villus sampling (CVS) and amniocentesis, even when performed by the most experienced of operators, pose a small but real risk of fetal injury and pregnancy loss.

Noninvasive aneuploidy diagnosis is now a reality in high-risk population screening

The holy grail of aneuploidy diagnosis would be a noninvasive way to sample fetal cells. Although we have known for decades that fetal cells enter the maternal circulation, it has been impractical to use them for aneuploidy testing because of their scarcity and longevity. In the 1990s, however, cell-free fetal DNA (cffDNA), a compound of DNA fragments of uncertain origin, was identified in maternal plasma. CffDNA is more plentiful than fetal cells. It also disappears within hours of delivery, demonstrating that it is specific to the current pregnancy.

CffDNA is already used in fetal Rh typing and gender determination in disorders such as congenital adrenal hyperplasia. Several studies in high-risk populations have demonstrated high sensitivity and specificity for the detection of Trisomies 21, 18, and 13. Several commercial tests are now available, although neither their accuracy nor their cost has been determined for use in low-risk population screening, compared with traditional testing.

Microarray analysis, paired with karyotyping, can elucidate ultrasound-identified fetal anomalies

Cytogenetic microarray analysis is also being explored in the prenatal period. Microarray analysis is currently used as a first-line test for infants and children who demonstrate developmental delay, autism spectrum disorders, dysmorphic features, and congenital anomalies. As many as 15% of patients with an otherwise normal karyotype will have a clinically significant copy number variant (CNV) on microarray. This finding has led to the use of microarray analysis in conjunction with karyotyping for fetuses with ultrasound-identified anomalies. Both targeted arrays (for syndromes associated with ultrasound anomalies) and whole-genome arrays are available.



Recent data from a study from the National Institute of Child Health and Human Development (NICHD) reveal that the prenatal detection rates for aneuploidy and unbalanced translocations are comparable between microarray analysis and karyotyping. Microarray analysis did not, however, detect triploidies or balanced translocations. As many as 6% of patients with a normal karyotype and structural anomalies and 1.7% of patients with advanced maternal age or positive screening tests had either a known or potentially clinically relevant CNV. This large study concluded that microarray analysis not only provides equal detection of aneuploidy but also more information in the form of CNVs, compared with karyotyping alone.

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