The Genetic Sonogram in Second Trimester Down Syndrome Screening

Second-trimester genetic sonogram for detection of fetal chromosomal abnormalities in a community-based antenatal testing unit

OBJECTIVE

To evaluate the efficacy of the second-trimester genetic sonogram for the detection of Down syndrome and other chromosomal abnormalities in a community-based antenatal testing unit.

METHODS

This was a retrospective study using data from two community hospital antenatal ultrasound units. Six hundred and sixty fetal ultrasound examinations in both at-risk (n = 581) and low-risk (n = 79) pregnancies were performed from 15 + 0 to 22 + 6 weeks' gestation and all cases were verified for outcome data. The sonographic detection of a major congenital anomaly or a sonographic marker (increased nuchal skinfold, short humerus, short femur, echogenic bowel, pyelectasis, echogenic intracardiac focus, absence or hypoplasia of fifth mid phalanx or choroid plexus cyst) was recorded. The entire group of 660 ultrasound examinations as well as subgroups with and without non-ultrasound risk factors for a fetal chromosomal abnormality were analyzed to determine the sensitivity, specificity, positive and negative predictive values and positive likelihood ratio for the detection of Down syndrome and other fetal chromosomal abnormalities.

RESULTS

There were 32 (4.85%) chromosomal abnormalities in our study population. Twelve (3.75%) of these were Down syndrome, of which eight (66.6%) had a positive ultrasound examination in the second trimester. Six of seven (85.7%) of the trisomy 18 fetuses, 2/2 of the trisomy 13 fetuses and 2/3 of the non-mosaic 45,X fetuses had positive sonograms. The overall detection rate for chromosomal abnormalities was 20/32 (sensitivity, 62.5%; specificity, 80.7%; negative predictive value, 97.7%; positive predictive value, 14.2%; positive likelihood ratio, 3.24). Major structural defects and sonographic markers, excluding hypoplastic fifth digit and choroid plexus cyst, occurred significantly more frequently in Down syndrome cases compared with normal ones.

CONCLUSIONS

In a community-based antenatal testing unit we have demonstrated a detection rate for fetal Down syndrome with the second-trimester genetic sonogram that is comparable to the range of sensitivities reported by larger centers involving primarily high-risk patients. However, only 12 of the 32 fetal chromosomal abnormalities that we encountered were Down syndrome.

Association of Ultrasound Findings with Decision to Continue Down Syndrome Pregnancies

OBJECTIVE

To evaluate the association of ultrasound findings and other factors with the decision to terminate trisomy-21-affected pregnancies.

METHODS

We performed a retrospective analysis of trisomy-21-affected pregnancies diagnosed prior to 24 weeks' gestation. Data were collected on maternal age, indications for prenatal diagnosis, gestational age at diagnosis, marital status, race, parity and ultrasound findings. Logistic regression, chi(2), t test and Fishers exact test were used for statistical analysis.

RESULTS

Fifty-nine pregnancies were identified with a termination rate of 72.9%. Termination rates were significantly lower in patients with major (50%) or minor (64%) ultrasound abnormalities than in patients with normal ultrasound exams (92%), p = 0.026 and 0.022, respectively. Patients who chose terminations were older (36.1 vs. 32.3), but this did not reach statistical significance (p = 0.059).

CONCLUSION

Patients with abnormal ultrasound results were more likely to continue a trisomy 21 pregnancy.

Ultrasound Findings After Screening for Down Syndrome Using the Integrated Test

OBJECTIVE

To evaluate the incidence and significance of fetal anomalies and "soft markers" after screening for Down syndrome using the integrated test.

METHODS

This study is a retrospective study of 2,332 women at University College London Hospitals, United Kingdom. All women were screened for Down syndrome by the integrated test. Subsequently, a detailed anomaly scan was performed. All scan reports and screening results were analyzed statistically using SPSS 11.0 software.

RESULTS

Sixty-eight (2.9%) patients were categorized as high risk. There were 12 cases affected by Down syndrome, 10 (10 of 68) in the high-risk group and two (two of 2,264) in the low-risk group. Soft markers or structural anomalies were found in 13.0% of the low-risk group, in 29.4% of the high-risk group, and in 50% of the fetuses affected by Down syndrome. Multiplying the likelihood ratio of each marker with the risk of Down syndrome from the integrated test reduced the false-positive rate of the integrated test from 2.5% to 1.8%, but was accompanied by a reduction in the detection rate from 83% to 75%.

CONCLUSION

Absence of structural anomalies or markers should not prevent offering karyotyping to women in the high-risk group, because this would result in a significant reduction in the detection rate of Down syndrome. Women screened as low risk by the integrated test who have isolated soft markers should not be offered an amniocentesis.

Women's and health professionals' preferences for prenatal testing for Down syndrome in Australia

AIM

To describe and compare women's and health professionals' preferences for prenatal screening tests for Down syndrome.

DESIGN

Cross-sectional questionnaire survey.

PARTICIPANTS AND SETTING

Women (n = 322) attending for a glucose challenge test at 26 weeks gestation and health professionals (266 midwives and 34 obstetricians) at the Royal Women's Hospital, Melbourne, between 13 December 2002 and 30 April 2003.

OUTCOME MEASURES

The relative value participants attach to attributes of Down syndrome screening tests as determined by conjoint analysis and ranking scales.

RESULTS

Women and health professionals shared similar relative values regarding the importance of detection rate of screening tests, according to coefficients from conjoint analysis models. However, health professionals placed higher relative values on timing of prenatal tests and risk associated with the subsequent diagnostic test than did women. Comparison of coefficients suggests that, compared with health professionals, women would wait longer and accept a greater decrease in detection rate for a test if it was safer. Using the more traditional ranking scale, the safest test was ranked first by 56% of women while 47% of health professionals ranked a test with the highest detection rate first. Equal proportions ( approximately 10%) in both groups ranked the earliest test first.

CONCLUSION

There is a general agreement between pregnant women and health professionals regarding the relative importance they attach to different attributes of a test. However, health professionals appeared to favour earlier timing of tests while women placed greater emphasis on safety. Utilising two different measures of preference demonstrated the complexity of decision-making.