Microarray analysis also has been used in the study of pregnancy loss and stillbirth because it does not require viable or intact tissue as a source of DNA—an advantage, compared with traditional karyotyping. A recent study from the Stillbirth Collaborative Research Network demonstrated that genetic results in cases involving stillbirth were obtained more frequently via microarray analysis (87.4%) than by karyotype (70.5%). In addition, more genetic abnormalities (aneuploidy, pathogenic CNVs, and CNVs of unknown clinical significance) were detected by microarray analysis. Investigators concluded that microarray analysis may be especially useful in cases involving stillbirth (when a karyotype cannot be obtained) and structural abnormalities.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
We want an accurate, completely risk-free genetic test that can be used for anyone. What we have so far is a technology that must be tested before it can be used in most of our patients—that is, the low-risk ones. We also have access to the fetus’ genetic code on a very specific level.
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.
Should microarray analysis replace routine prenatal genetic testing?
A major dilemma associated with this technology is the significant amount of time that may be needed to counsel patients when the results are of unclear clinical significance.5 If the fetus has an anomaly, and a related CNV is identified, then counseling of the parents is fairly straightforward. However, if the fetus has an anomaly and a CNV that has not yet been defined, what should the parents be told? Some argue that this information should not be shared with the parents, whereas others recommend full disclosure of all results—even if we do not yet know what to make of them.
Another issue with microarray analysis is its inability to detect balanced translocations, triploidies, and low-level mosaicism, which require either a karyotype or whole-genome sequencing. Microarray analysis is also more expensive than karyotyping, although this may change in the future.
>Fetal therapy involves a complex equation of potential benefits and risks
Adzick NS, Thom EA, Spong CY, et al; MOMS Investigators. A randomized trial of prenatal versus postnatal repair of myelomeningocele. N Engl J Med. 2011;364(11):993–1104.
Fetal therapy is broadly defined as any intervention administered to or via the mother with a primary indication to improve perinatal or long-term outcomes for the fetus or newborn. The concept of intervening to prevent the death of a fetus by correcting an anatomic anomaly or halting a disease process in utero is not new. Liley performed the first intrauterine fetal transfusion for Rh alloimmunization in the 1960s. Today, we perform fetal interventions routinely to reduce mortality by giving medical therapy to the mother, such as antenatal corticosteroids to enhance fetal lung maturity or anti-arrhythmics for supraventricular tachycardia. More invasive procedures have proved to be lifesaving (placental laser coagulation for twin-twin transfusion syndrome), ameliorating in the short term (shunting for lower urinary tract obstruction to relieve oligohydramnios), or ultimately not helpful (decompression of hydrocephalus).
Most recently, open fetal surgery has taken center stage as an intervention focused not only on reducing mortality but on improving function and quality of life for fetuses with open neural tube defects (ONTDs). This anomaly was targeted for fetal intervention because, although ONTDs are not generally considered lethal, a significant number of patients die before the age of 5, the majority of patients require shunts that leave them vulnerable to complications, and ONTDs generally impose lifelong intellectual and physical limitations. Repair during fetal life was proposed to prevent damage to the spinal cord and reverse hindbrain herniation, with the goal of improving long-term neurologic function.
The Management of Myelomeningocele Study (MOMS) is a prospective, multicenter trial that randomly assigned fetuses with isolated ONTDs to open fetal repair of myelomeningocele via hysterotomy or to postnatal repair of the defect. Forty percent of infants who underwent fetal repair required placement of a shunt, compared with 82% of those who had postnatal repair (relative risk, 0.48; 97.7% CI, 0.36 to 0.64; P<.001). Infants in the fetal-repair group also had significantly improved composite scores for mental development and motor function at 30 months (P = .007), as well as improvement in secondary outcomes such as hindbrain herniation and independent walking at 30 months.
As exciting as these results are, open fetal surgery still has significant limitations. The few centers that perform the most complex surgeries often have strict exclusion criteria, including maternal body mass index (BMI) greater than 35 kg/m2 and other medical comorbidities. The surgery also poses real risks for both mother and fetus. In the MOMS trial, the risk of preterm labor increased in the fetal-repair group, compared with postnatal repair (38% vs 14%), as did the risk of premature rupture of membranes (46% vs 8%). The fetal-repair group delivered more than 3 weeks earlier than the postnatal repair group (34 vs 37 weeks). Twenty-five percent of the fetal-repair group had thinning of the uterine scar, with uterine dehiscence seen in 10%. When myelomeningocele is repaired during fetal life, mothers require two hysterotomies during pregnancy and face an increased risk of uterine rupture and preterm delivery in subsequent pregnancies. The use of tocolytics exposes these mothers to an increased risk of pulmonary edema (6% in the fetal-repair group vs 0% for postnatal repair).