Screening for Aneuploidy in Multiple Gestations

Performance and Diagnostic Value of Genome-Wide Noninvasive Prenatal Testing in Multiple Gestations

OBJECTIVE

To evaluate the accuracy and diagnostic value of genome-wide noninvasive prenatal testing (NIPT) for the detection of fetal aneuploidies in multiple gestations, with a focus on dichorionic-diamniotic twin pregnancies.

METHODS

We performed a retrospective cohort study including data from pregnant women with a twin or higher-order gestation who underwent genome-wide NIPT at one of the eight Belgian genetic centers between November 1, 2013, and March 1, 2020. Chorionicity and amnionicity were determined by ultrasonography. Follow-up invasive testing was carried out in the event of positive NIPT results. Sensitivity and specificity were calculated for the detection of trisomy 21, 18, and 13 in the dichorionic-diamniotic twin cohort.

RESULTS

Unique NIPT analyses were performed for 4,150 pregnant women with a multiple gestation and an additional 767 with vanishing gestations. The failure rate in multiple gestations excluding vanishing gestations ranged from 0% to 11.7% among the different genetic centers. Overall, the failure rate was 4.8%, which could be reduced to 1.2% after single resampling. There were no common fetal trisomies detected among the 86 monochorionic-monoamniotic and 25 triplet cases. Two monochorionic-diamniotic twins had an NIPT result indicative of a trisomy 21, which was confirmed in both fetuses. Among 2,716 dichorionic-diamniotic twin gestations, a sensitivity of 100% (95% CI 74.12-100%) and a specificity of 100% (95% CI 99.86-100%) was reached for trisomy 21 (n=12). For trisomy 18 (n=3), the respective values were 75% (95% CI 30.06-95.44%) sensitivity and 100% (95% CI 99.86-100%) specificity, and for trisomy 13 (n=2), 100% (95% CI 20.65-100%) sensitivity and 99.96% (95% CI 99.79-99.99%) specificity. In the vanishing gestation group, 28 NIPT results were positive for trisomy 21, 18, or 13, with only five confirmed trisomies.

CONCLUSION

Genome-wide NIPT performed accurately for detection of aneuploidy in dichorionic-diamniotic twin gestations.

Isolated absence of nasal bone in 1 fetus in a dizygotic pregnancy after in vitro fertilization: A case report

RATIONALE

During ultrasound prenatal screening, absence of the fetal nasal bone is used as a marker for common aneuploidies in singleton pregnancies. However, its application in multiple pregnancies is less sensitive and more challenging owing to difficulties in obtaining adequate views of the fetal face.

PATIENT CONCERNS

A 38-year-old woman with dichorionic-diamniotic (DCDA) pregnancy and a history of in vitro fertilization and embryo transfer was referred to our hospital with the absence of the nasal bone noted on ultrasound images obtained during the second trimester in 1 fetus.

DIAGNOSIS

Prenatal sonographic examination revealed the absence of the nasal bone in 1 fetus in the DCDA gestation. Amniocentesis performed on the dual amniotic sacs revealed normal karyotypes for each twin. The absence of the nasal bone was confirmed on a radiograph obtained postnatally in 1 infant.

INTERVENTIONS

The mother underwent routine outpatient care according to the gestational age and successfully delivered following lower-segment cesarean section.

OUTCOMES

Two live infants were uneventfully delivered. Radiography confirmed the absence of the nasal bone in 1 of the newborns on postnatal day 3. The infants were followed up until 2 years and 9 months of age, which revealed normal appearance and eating and breathing functions.

LESSONS

Prenatal diagnosis of the absence of nasal bone in 1 fetus of DCDA pregnancy has rarely been reported. Although a fetus with the absence of the nasal bone in DCDA gestation poses a significant risk of aneuploidy, it is acceptable when the defect is an isolated anomaly after ruling out genetic abnormalities. Appropriate consultation should be provided for these patients.

Management of multiple gestations

Multiple gestations are commonly encountered in both high-risk and low-risk pregnancies and, since the advent of assisted reproductive technologies in the 1980s, the numbers of multiple gestations have grown rapidly. Thus, an understanding of both the maternal and fetal risks associated with multiple gestations should be central to all obstetric practice. The ability to foresee issues and the know how to respond to the complications that develop are central to the correct management of these pregnant women. For some, appropriate management may include referral to a specialist maternal and fetal medicine physician or, in some cases, to a specialist fetal center. The present review provides a comprehensive and simplified overview of multiple gestations, including incidence, diagnosis, genetic considerations, complications (both general and specific to multiple gestation subtypes), and delivery management. It is essential that providers recognize the high-risk and specific complications that may affect a multiple gestation in order to provide the highest possible level of care for these pregnant women.

A new era in aneuploidy screening: cfDNA testing in >30,000 multifetal gestations: Experience at one clinical laboratory

Since introducing cell-free DNA screening, Sequenom Laboratories has analyzed over 1 million clinical samples. More than 30,000 of these samples were from multifetal gestations (including twins, triplets and higher-order multiples). The clinical laboratory experience with the first 30,000 multifetal samples will be discussed. Maternal plasma samples from multifetal gestations were subjected to DNA extraction and library preparation followed by massively parallel sequencing. Sequencing data were analyzed to identify autosomal trisomies and other subchromosomal events. Fetal fraction requirements were adjusted in proportion to fetal number. Outcome data, when voluntarily received from the ordering provider, were collected from internal case notes. Feedback was received in 50 cases. The positivity rate in multifetal samples for trisomy 21 was 1.50%, 0.47% for trisomy 18, and 0.21% for trisomy 13. Average total sample fetal fraction was 12.2% at a mean gestational age of 13 weeks 6 days. Total non-reportable rate was 5.95%. Estimated performance based on ad hoc clinical feedback demonstrates that possible maximum sensitivity and specificity meet or exceed the original performance from clinical validation studies. Cell-free DNA (cfDNA) screening provides certain advantages over that of conventional screening in multifetal gestations and is available in higher-order multiples.