An Unusual Case: Testing for Fetal Trisomy Abnormalities in Maternal Blood At 33 Weeks Gestation
Title: An Unusual Case: Testing for Fetal Trisomy Abnormalities in Maternal Blood At 33 Weeks Gestation
- Describe the basics of fetal DNA testing in maternal blood.
- Describe the consequences of being diagnosed with Trisomy 18.
- Describe the benefits of noninvasive prenatal testing
Background:
Our patient was transferred to us at 33 weeks gestation when an ultrasound detected anhydramnios. Genetic testing was offered multiple times due to known fetal anomalies, but she declined. Amniocentesis was no longer an option secondary to anhydramnios; however, Trisomy 18 was suspected, so prenatal diagnosis and confirmation was recommended. Transabdominal CVS was attempted, but unsuccessful. A relatively new procedure of testing the maternal blood for fetal DNA to detect aneuploidy abnormalities was considered a solution.
Case:
Ultrasound indicated a single umbilical artery, cleft lip, abnormal kidneys, absent bladder, and rocker bottom feet. She was counseled regarding the significant risk of neonatal death if this was Trisomy 18, but insisted on full resuscitative measures and a caesarean for fetal distress. Ironically, she had a Category I fetal monitor strip, so her BPP was 2/10.
The transabdominal CVS was unsuccessful because only maternal cells were obtained. MFM decided on a relatively new procedure where fetal DNA is extrapolated from maternal blood, after which it can be tested for aneuploidy. It was sent to an outside lab to be tested for Trisomies 18, 13 and 21.
Before results were obtained, the fetus started showing signs of compromise: MCA cephalization on ultrasound, and variable decelerations, which became increasingly prolonged. When pericardial effusion was noted on ultrasound, the patient was induced.
SVD of a female, apgars 5/8. Bilateral cleft lip and palate, small head and contracted hands and feet were noted. Karyotyping on the newborn revealed Turner Syndrome and Trisomy 16.
Conclusion:
In 1997, the detection of fetal DNA in maternal circulation suggested the future of noninvasive prenatal testing. It is estimated that 95% of all women opt for prenatal screening. Reasons may include the desire to prepare for the birth of an affected child; preparation for the possibility of an in utero or neonatal death; planning for the time, mode and place of delivery; planning for specialists to care for the affected child; and options for termination. Invasive tests carry a risk of injury to the fetus and are not 100% accurate. Fetal DNA testing for aneuploidy has been reported to have 98-99% specificity. This was our first encounter with transabdominal CVS as well as fetal DNA testing in maternal blood. We are interested in the impact on the future.
Keywords:
fetal DNA, Trisomy, fetal anomaly