Contingent screening for Down syndrome completed in the first trimester: a multicenter study

OBJECTIVE

To assess a new contingent screening strategy for Down syndrome completed in the first trimester.

METHODS

First-trimester screening combining nuchal translucency thickness measurement and assessment of serum analytes (combined test) was offered to pregnant women who presented for prenatal care during the first trimester to nine health centers and community hospitals in the area served by the Catalan Public Health Service. If an intermediate risk (1/101-1/1000) for Down syndrome was identified, women were referred to the Hospital Clinic Barcelona for risk reassessment that included the use of secondary ultrasound markers (nasal bone, ductus venosus blood flow and tricuspid flow). Intermediate-risk women were divided into two subgroups for further analysis: high-intermediate risk (1/101-1/250) and low-intermediate risk (1/251-1/1000). We compared feasibility and efficacy of both combined and contingent screening strategies.

RESULTS

The combined test, the first screening stage, was performed in 16 001 pregnant women, of whom 1617 (10.1%) were found to have an intermediate risk. Further division of this group showed that 1.8% (n = 289) of women were at high-intermediate risk and 8.3% (n = 1328) at low-intermediate risk. The contingent screening strategy significantly reduced the false-positive rate, from 3.0% to 1.3-1.8% (P < 0.001), without affecting the detection rate (which was 75-79% and 76%, with and without the contingent screening strategy, respectively). However, only 45% of intermediate-risk patients underwent the second screening step due to a preference among high-intermediate-risk (1/101-1/250) women for invasive testing and to low uptake among low-intermediate-risk (1/251-1/1000) women.

CONCLUSIONS

The proposed first-trimester contingent strategy reduces the screen false-positive rate without impacting on the detection rate of Down syndrome. The low compliance observed in our study may prevent its use in certain populations.

First-trimester detection of structural abnormalities and the role of aneuploidy markers

OBJECTIVES

To determine the sensitivity of first-trimester ultrasound for diagnosing different structural anomalies in chromosomally normal pregnancies, and to establish the role of aneuploidy markers in the detection of abnormalities.

METHODS

This was a retrospective study of chromosomally normal singleton pregnancies with an 11-14-week scan performed in our center during 2002-2009. The ultrasound examination included an early fetal anatomy survey and assessment of nuchal translucency, ductus venosus blood flow and nasal bone.

RESULTS

Among 13 723 scanned first-trimester pregnancies with no genetic anomalies and complete follow-up, 439 fetuses (3.2%) were found to present with structural anomalies (194 with major anomalies and 245 with only minor anomalies). Forty-nine per cent of major structural anomalies were detected during the first-trimester scan, the highest rates corresponding to acrania (17/17), holoprosencephaly (three of three), hypoplastic left heart syndrome (10/10), omphalocele (six of six), megacystis (seven of eight) and hydrops (eight of nine). Higher than expected detection rates were obtained for skeletal (69%) and cardiac (57%) defects, coincidentally showing the highest presence of an increased nuchal translucency or abnormal ductus venosus blood flow (38% and 52%, respectively). The finding of an absent nasal bone did not appear to be associated with structural defects.

CONCLUSION

About half of major structural abnormalities can be diagnosed in the first trimester. Increased nuchal translucency or abnormal ductus venosus blood flow appear to be associated with cardiac and skeletal defects and may facilitate early detection.

Increased nuchal translucency and normal karyotype: perinatal and pediatric outcomes at 2 years of age

OBJECTIVE

To assess the perinatal and pediatric outcomes up to 2 years of age in singleton karyotypically normal fetuses with increased nuchal translucency (NT) above the 99(th) percentile.

METHODS

Singleton fetuses with NT above the 99(th) percentile and normal karyotype scanned in our center from 2002 to 2006 were included. Work-up included first- and second-trimester anomaly scan, first- and second-trimester fetal echocardiography, and in selected cases infection screening and genetic testing. Among survivors, a pediatric follow-up up to 2 years of age was undertaken.

RESULTS

During this 4-year period, 171 singleton fetuses with NT above the 99(th) percentile and normal karyotype were included in the study. There were seven spontaneous fetal losses, 38 terminations of pregnancy and two postnatal deaths. Among the 124 (72.5%) survivors, 12 (9.7%) were born with structural abnormalities. Neurodevelopmental follow-up was completed in 108 (87.1%) of the 124 survivors and four (3.7%) showed moderate to severe impairment. Overall, a structural abnormality or genetic syndrome was diagnosed in 50 fetuses/newborns. Prenatal diagnosis was achieved for 83.8% (31/37) of the structural abnormalities and 69.2% (9/13) of the genetic syndromes. Interestingly, a single umbilical artery was found in six fetuses with no structural defects at birth, five of which had a long-term favorable outcome (4.5%), and in one 22q11 microdeletion syndrome was diagnosed at 2 years of age.

CONCLUSION

Singleton fetuses with an increased NT above the 99(th) percentile and normal karyotype showed a 63% intact survival. Long-term neurodevelopmental outcome among survivors did not appear to differ from that reported for the general population.

The CUSUM test applied in prospective nuchal translucency quality review

OBJECTIVES

To design a cumulative sum (CUSUM) test for prospective nuchal translucency (NT) measurement quality review that is as stringent as the retrospective quality review methods based on distribution parameters currently in use.

METHODS

The database including all fetal NT measurements obtained during a 2-year period in a single center was reviewed, and measurements obtained by sonologists who measured fewer than 100 cases were excluded. The NT distribution parameters proposed by The Fetal Medicine Foundation (FMF) and the Women & Infants Hospital of Rhode Island (WIHRI) were assessed in the whole NT series and in sonologist-specific distributions. A previously described CUSUM model was adapted to fulfil our objective.

RESULTS

Two thousand four hundred and seventy-five NT measurements were obtained by seven sonologists during the study period (January 2007-December 2008). In the assessment of sonologist-specific NT distributions, two sonologists fulfilled all the FMF and WIHRI criteria, one showed NT overestimation and four failed due to NT underestimation. Our new CUSUM test model, based on multiples of the median deviations, showed good agreement with the FMF and WIHRI methods in the assessment of sonologist-specific performance.

CONCLUSIONS

Our CUSUM test model showed close agreement with the retrospective quality review methods based on distribution parameters currently in use, but with the advantage that it can be applied prospectively, allowing for earlier correction of deviations from target performance.

Prevalence and perinatal outcome of dichorionic and monochorionic twins with nuchal translucency above the 99(th) percentile and normal karyotype

OBJECTIVE

To evaluate the prevalence of and perinatal outcome associated with increased nuchal translucency thickness (NT) > 99(th) percentile in dichorionic and monochorionic twins with normal karyotype.

METHODS

Two hundred and six consecutive twin pregnancies (166 dichorionic and 40 monochorionic) underwent an NT scan during a 4-year period. In those with NT > 99(th) percentile and normal karyotype, we performed first- and second-trimester anomaly scans, fetal echocardiography at 14-16 and 20-22 weeks, maternal serology and, in monochorionic pregnancies, serial ultrasound examinations every other week. Perinatal outcome was recorded.

RESULTS

There were 10 (4.95%) pregnancies in which one of the fetuses had NT > 99(th) percentile and normal karyotype, including five fetuses (1.5%) in dichorionic and five (6.25%) in monochorionic pregnancies. During the same period the prevalence of NT > 99(th) percentile and normal karyotype in singleton pregnancies studied in our center was 2.6%. Among the 10 twins affected, six (60%) were diagnosed with structural abnormalities (three dichorionic and three monochorionic), and two intrauterine fetal demises occurred (one dichorionic and one monochorionic). Thus, the perinatal outcome was normal in only two of the pregnancies, one dichorionic and one monochorionic.

CONCLUSIONS

The prevalence of NT > 99(th) percentile in dichorionic twins with a normal karyotype is similar to that in singletons. In monochorionic twins we confirmed previous studies reporting an increased prevalence compared with singletons. NT > 99(th) percentile with a normal karyotype in twins was associated with a high rate of fetal abnormalities and/or fetal demise (overall 80%) irrespective of chorionicity.