Expected performance of second trimester maternal serum testing followed by a 'genetic sonogram' in screening of fetal Down syndrome

Efficacy of the genetic sonogram in a stepwise sequential protocol for down syndrome screening

OBJECTIVES

The purpose of this study was to evaluate the efficacy of the genetic sonogram in Down syndrome screening for women who have received the stepwise sequential test.

METHODS

This retrospective cohort study included women with singleton pregnancies who underwent stepwise sequential (first-trimester combined and second-trimester serum) screening and then had a genetic sonogram between March 2005 and January 2010. Stepwise sequential Down syndrome risks were multiplied by either a positive or negative likelihood ratio based on the second-trimester sonographic findings to determine the final Down syndrome risk. A final Down syndrome risk of 1:270 or higher was considered screen positive.

RESULTS

A total of 6286 women fulfilled our criteria, including 17 with Down syndrome-affected fetuses. After stepwise sequential testing, the Down syndrome detection rate was 88.2% (15 of 17), and after the genetic sonogram, there was a non-significant reduction in detection to 82.4% (14 of 17; P > .05). For the 6269 unaffected pregnancies, the genetic sonogram converted 58 screen-negative results (1%) to positive and 183 screen-positive results (3.1%) to negative. The net effect was a change in the false-positive rate from 6.2% (390 of 6269) after stepwise sequential screening to 4.2% (266 of 6269) after the genetic sonogram.

CONCLUSIONS

The genetic sonogram should be applied cautiously for women who have received prior prenatal screening tests. Women with screen-positive results need to be counseled that a negative sonographic result can be falsely reassuring. Conversely, for women with screen-negative results who have a risk close to the cutoff, a sonographic examination could assist in the decision of whether to accept or reject amniocentesis.

Role of fetal echocardiography in stepwise sequential screening for chromosomal disorders (combined test associated with modified genetic sonography)

OBJECTIVES

To evaluate the contribution made by fetal echocardiography in identifying Down's syndrome (DS) and other chromosomal disorders in a stepwise sequential screening method (first step: combined test (CT), second step: modified genetic sonography (MGS) (major malformation and nuchal fold)), for DS in the general population of pregnant women.

METHODS

Prospective study. During a 5-year study period (July 2005-June 2010) 17,911 pregnant women underwent CTs with MGS (with fetal cardiac morphological evaluation performed by obstetricians in a tertiary hospital) as a screening method for DS. We evaluated the sensitivity and false positive rate (FPR) (95% confidence interval (CI)) of three screening methods for DS and all chromosomal disorders: CT, CT + MGS, and CT + fetal echocardiography.

RESULTS

A total of 17,911 cases were analyzed with 67 chromosome disorders and 45 DS cases being found. For DS, the CT sensitivity was 80% (95% CI; 68.3-91.7) (36/45) and 79.1% (95% CI; 69.4-88.8) (53/67) for all chromosome disorders, with a FPR of 4.2% (95% CI; 3.9-4.5) (752/17,866) and 4.1% (95% CI; 3.8-4.4) (735/17,844), respectively. For CT + MSG and CT + fetal echocardiography, the sensitivity for DS was 93.3% (95% CI; 85.9-0.99) (42/45) and 95.5% (95% CI; 90.5-0.99) (64/67) for all chromosome disorders. The FPR for CT + MSG was 4.8% (95% CI; 4.5-5.1) (860/17,866) and 4.6% (95% CI; 4.3-4.9) (836/17,844), respectively. The FPR of CT + fetal echocardiography was 4.4% (95% CI; 4.1-4.7) (792/17,866) for DS screening and 4.3% (95% CI; 4-4.6) (770/17,844) for chromosome abnormality screening.

CONCLUSIONS

Fetal echocardiography is highly capable of identifying DS and other chromosomal disorders as a part of genetic sonography in stepwise sequential screening.

Contribution of "modified genetic sonography" to the combined test as a screening method for chromosomal abnormalities

OBJECTIVES

We propose to assess the contribution of "modified genetic sonography" (MGS) to the combined test (CT) as a method of stepwise sequential screening (1st step: CT, 2nd step: MGS) for chromosome abnormalities in the general population of pregnant women.

METHODS

Prospective study. During a 4 year study period (July 2005-June 2009) 16,548 pregnancies underwent a CT combined with MGS (major malformation and nuchal fold) as a screening method for chromosome abnormalities. We assessed sensitivity and false positive rate (FPR) (95% CI).

RESULTS

We offered a chromosome abnormalities screening test to 96.6% of pregnancies (15,995 cases). 14,160 cases are analyzed (1st step: CT, 2nd step: MGS) including 49 chromosome abnormalities and 35 Down's syndrome (DS). The sensitivity of CT for DS was 77.1% [95% CI, 63.2-91] (27/35) and 77.5% for all chromosome abnormalities [95% CI, 65.8-89.2] (38/49) with a FPR of 4.4% [95% CI, 4.1-4.7]. If MGS was combined with CT, the sensitivity for DS was 91.4% [95% CI, 82.1-99] (32/35) and 93.8% for all chromosome abnormalities [95% CI, 87-99] (46/49) for a FPR of 5.1% [95% CI, 4.7-5.5].

CONCLUSIONS

The addition of an MGS to combined first-trimester screening test for aneuploidy improved sensitivity by 14.3% while only increasing the FPR by 0.7%.

Model-predicted performance of second-trimester Down syndrome screening with sonographic prenasal thickness

OBJECTIVE

The purpose of this study was to estimate the Down syndrome detection and false-positive rates for second-trimester sonographic prenasal thickness (PT) measurement alone and in combination with other markers.

METHODS

Multivariate log Gaussian modeling was performed using numerical integration. Parameters for the PT distribution, in multiples of the normal gestation-specific median (MoM), were derived from 105 Down syndrome and 1385 unaffected pregnancies scanned at 14 to 27 weeks. The data included a new series of 25 cases and 535 controls combined with 4 previously published series. The means were estimated by the median and the SDs by the 10th to 90th range divided by 2.563. Parameters for other markers were obtained from the literature.

RESULTS

A log Gaussian model fitted the distribution of PT values well in Down syndrome and unaffected pregnancies. The distribution parameters were as follows: Down syndrome, mean, 1.334 MoM; log(10) SD, 0.0772; unaffected pregnancies, 0.995 and 0.0752, respectively. The model-predicted detection rates for 1%, 3%, and 5% false-positive rates for PT alone were 35%, 51%, and 60%, respectively. The addition of PT to a 4-serum marker protocol increased detection by 14% to 18% compared with serum alone. The simultaneous sonographic measurement of PT and nasal bone length increased detection by 19% to 26%, and with a third sonographic marker, nuchal skin fold, performance was comparable with first-trimester protocols.

CONCLUSIONS

Second-trimester screening with sonographic PT and serum markers is predicted to have a high detection rate, and further sonographic markers could perform comparably with first-trimester screening protocols.

Role of second-trimester genetic sonography after Down syndrome screening

OBJECTIVE

To estimate the effectiveness of second-trimester genetic sonography in modifying Down syndrome screening test results.

METHODS

The First and Second Trimester Evaluation of Risk (FASTER) aneuploidy screening trial participants were studied from 13 centers where a 15- to 23-week genetic sonogram was performed in the same center. Midtrimester Down syndrome risks were estimated for five screening test policies: first-trimester combined, second-trimester quadruple, and testing sequentially by integrated, stepwise, or contingent protocols. The maternal age-specific risk and the screening test risk were modified using likelihood ratios derived from the ultrasound findings. Separate likelihood ratios were obtained for the presence or absence of at least one major fetal structural malformation and for each "soft" sonographic marker statistically significant at the P<.005 level. Detection and false-positive rate were calculated for the genetic sonogram alone and for each test before and after risk modification.

RESULTS

A total of 7,842 pregnancies were studied, including 59 with Down syndrome. Major malformations and 8 of the 18 soft markers evaluated were highly significant. The detection rate for a 5% false-positive rate for the genetic sonogram alone was 69%; the detection rate increased from 81% to 90% with the combined test, from 81% to 90% with the quadruple test, from 93% to 98% with the integrated test, from 97% to 98% with the stepwise test, and from 95% to 97% with the contingent test. The stepwise and contingent use of the genetic sonogram after first-trimester screening both yielded a 90% detection rate.

CONCLUSION

Genetic sonography can increase detection rates substantially for combined and quadruple tests and more modestly for sequential protocols. Substituting sonography for quadruple markers in sequential screening was not useful.

LEVEL OF EVIDENCE

II.

Down syndrome screening in the United States in 2001 and 2007: a survey of maternal-fetal medicine specialists

OBJECTIVE

The purpose of this study was to determine changes in screening and performance of invasive diagnostic procedures for Down syndrome between 2001 and 2007.

STUDY DESIGN

The Society for Maternal-Fetal Medicine members completed a survey in 2007 regarding screening tests and diagnostic procedures for Down syndrome. With the use of descriptive statistics, the chi(2) test, and the Student t test, responses from 2007 were compared with responses from a similar 2001 survey.

RESULTS

Performance of first-trimester screening more than doubled from 2001-2007 (43.1% in 2001, 97.3% in 2007; P < .0001). Between 2001 and 2007, the use of the quad screen increased 10-fold (8.5% in 2001, 85.6% in 2007; P < .0001). There was an estimated 20% decrease in invasive diagnostic procedures that were performed in risk-positive women (53.7% in 2001, 34.2% in 2007; P < .0001). In 2007, the average fetal loss rates that were quoted by maternal-fetal medicine specialists after chorionic villous sampling was 1:160 and after an amniocentesis was 1:493.

CONCLUSION

Down syndrome screening evolved from 2001-2007, with an increasing emphasis on first-trimester screening. With more efficacious screening, the number of invasive procedures has declined.