Genetic sonography: an option for women of advanced maternal age with negative triple-marker maternal serum screening results

Association between chromosome abnormities and prenatal diagnosis indicators screening in the second trimester of pregnancy

This study aimed to explore the prenatal indicators in the second trimester of pregnancy and their association with chromosome abnormities (CA) to guide decisions toward invasive diagnostic procedures. Pregnant women who underwent prenatal screening and underwent amniocentesis in the second trimester in our Hospital between June 2017 and February 2019 were included in this retrospective cohort study. The reason for amniocentesis in prenatal screening and diagnoses was extracted from the charts. Finally, 3449 pregnant women were included. Of them, 181 were with CA confirmed by amniocentesis (i.e., the CA group), while 3268 were without CA (i.e., the non-CA group). Compared with the women in the non-CA group, those in the CA group were more likely to be older (30 [27,32] vs 29 [26,31], P < .001), had higher gestational weeks (20 [19,23] vs 19 [18,23], P = .008), an increased risk of advanced maternal age (AMA) (9.4% vs 2.2%, P < .001), had an increased risk of NIPT (IRN) (5.1% vs 1.9%, P < .001), had higher rates of a parental chromosome abnormality (PCA) (1.8% vs 0.9%, P = .002), and had increased risk of trisomy 21 (IRT21) (63.0% vs 45.3%, P < .001). AMA (OR = 4.22, 95% CI: 2.35-7.58, P < .001; AUC = 0.536), IRN (OR = 10.62, 95% CI: 6.66-16.94, P < .001; AUC = 0.589), PCA (OR = 4.77, 95% CI: 2.01-11.32, P < .001; AUC = 0.584), and IRT21 (OR = 0.67, 95% CI: 0.47-0.89, P = .008; AUC = 0.515) were independently associated with CA. AMA, IRN, IRT21, and PCA during the second trimester were independently associated with CA, but their predictive values for CA were relatively low. Combining those indicators may improve the predictive value.

Influence of second-trimester ultrasound markers for Down syndrome in pregnant women of advanced maternal age

The objective of the present study was to evaluate the influence of second-trimester ultrasound markers on the incidence of Down syndrome among pregnant women of advanced maternal age. This was a retrospective cohort study on 889 singleton pregnancies between the 14th and 30th weeks, with maternal age ≥ 35 years, which would undergo genetic amniocentesis. The second-trimester ultrasound assessed the following markers: increased nuchal fold thickness, cardiac hyperechogenic focus, mild ventriculomegaly, choroid plexus cysts, uni- or bilateral renal pyelectasis, intestinal hyperechogenicity, single umbilical artery, short femur and humerus length, hand/foot alterations, structural fetal malformation, and congenital heart disease. To investigate differences between the groups with and without markers, nonparametric tests consisting of the chi-square test or Fisher's exact test were used. Moreover, odds ratios with their respective 95% confidence intervals were calculated. Out of the 889 pregnant women, 131 (17.3%) presented markers and 758 (82.7%) did not present markers on the second-trimester ultrasound. Increased nuchal fold (P < 0.001) and structural malformation (P < 0.001) were the markers most associated with Down syndrome. The presence of one marker increased the relative risk 10.5-fold, while the presence of two or more markers increased the risk 13.5-fold. The presence of markers on the second-trimester ultrasound, especially thickened nuchal fold and structural malformation, increased the risk of Down syndrome among pregnant women with advanced maternal age.

The history of the second-trimester sonographic markers for detecting fetal Down syndrome, and their current role in obstetric practice

This review summarizes the development, history and use of second-trimester sonographic markers for the detection of fetal Down syndrome over three decades. Starting with the nuchal fold thickening in 1985 and culminating in the genetic sonogram in the 1990 s. The combination of second-trimester serum screening with the ultrasound markers improved the detection rate of affected fetuses but also allowed patients to decrease their risk of carrying a fetus with Down syndrome if the genetic sonogram was normal. More recently the role of the genetic sonogram and its markers have changed with the wide spread use of first-trimester screening. This prior screening ultimately decreases the prevalence of fetal Down syndrome in the second trimester to less than 85% of what it was in the first-trimester as most fetuses with Down syndrome are now identified early. Current interpretation of the second-trimester Down syndrome markers must be based on the result of the first trimester and combined screening to achieve the most accurate risk estimate of an affected fetus.

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

OBJECTIVE

To assess the efficacy of screening for fetal Down syndrome through the sequential provision of second trimester maternal serum tests and fetal ultrasound (the 'genetic sonogram').

METHODS

Monte Carlo modeling was used to generate typical results for second trimester serum screening. Serum test likelihood ratios were then multiplied by likelihood ratios associated with the provision of a genetic sonogram. The impact of adding the genetic sonogram on the detection rate (DR) and false-positive rate (FPR) were assessed for typical protocols that are currently in use. The effect of expanding the number of women who receive the genetic sonogram, variation in the marker frequencies in the genetic sonogram, and a multivariate Gaussian model that incorporated both serum and ultrasound measurements as continuous variables were also considered.

RESULTS

When the genetic sonogram is offered only to those women who are screen-positive by serum testing, there can be a substantial reduction in the number of women with an indication for amniocentesis but also some loss in detection. The extent of these changes will partially depend on the serum tests and cutoff used. Providing the genetic sonogram to more women can reduce loss in detection without resulting in high amniocentesis rates. As a sequential screening tool, the genetic sonogram can be improved by incorporating markers that have a high frequency in affected pregnancies and by using ultrasound measurements as continuous variables.

CONCLUSION

It should be possible to provide highly effective multistep screening protocols that maximize the benefits of both maternal serum and ultrasound while minimizing the amount of testing offered.

Fetal nasal bone assessment in first trimester down syndrome screening

OBJECTIVE

To evaluate the contribution of nasal bone assessment in the first trimester Down syndrome screening.

METHODS

The fetuses which underwent first trimester screening with nuchal translucency (NT) measurement were evaluated for the absence or presence of nasal bone according to the instructions described by the Fetal Medicine Foundation, London.

RESULTS

Among the 1,807 fetuses included in the study, 9 had trisomy 21. The detection rate of Down syndrome with NT measurement was 77.8% (7/9) with a false-positive rate of 4.5%. Incorporation of biochemical tests (PAPP-A, and free beta-hCG measurement) into the screening increased the detection rate to 88.9% (8/9) and decreased the false-positive rate to 3.6%. The prevalence of absent nasal bone was 7/1,798 (0.39%) in chromosomally normal fetuses, and 3/9 (33.3%) in Down syndrome fetuses. Sensitivity, specificity, positive predictive and negative predictive values of absence of nasal bone for trisomy 21 are 33.3% (CI: 0.12-0.64), 99.6% (CI: 0.99-0.99), 30% (95% CI: 0.11-0.53) and 99.7% (95% CI: 0.99-0.99), respectively. The positive likelihood ratio of absent nasal bone was 85.6 (95% CI: 26.2-279.5), and the negative likelihood was 0.67 (95% CI: 0.42-1.06). When nasal bone assessment was incorporated into the NT risk assessment or combined test, the detection rate of trisomy 21 was not changed, however, the false-positive rate decreased to 3.4 and 3%, respectively.

CONCLUSION

The absence of fetal nasal bone has a high positive likelihood ratio for Down syndrome in the first trimester screening, and the presence of nasal bone may potentially lower the need for invasive testing.

The role of the second trimester genetic sonogram in screening for fetal Down syndrome

The Genetic Sonogram is an ultrasound examination done on second trimester fetuses that not only evaluates the fetus for structural malformations, but also searches for the sonographic markers of fetal Down syndrome. The main markers that comprise the genetic sonogram include the nuchal fold, short femur and humerus, pyelectasis, hyperechoic bowel, echogenic intracardiac focus, and any major abnormality. The absence of any marker on a second trimester scan conveys a 60-80% reduction in prior risk of Down syndrome based on advanced maternal age or serum screen risk. The presence of sonographic markers, either singly or in combination, will raise the baseline risk of Down syndrome using likelihood ratios calculated for each individual marker. Using this approach, approximately 75% of fetuses with Down syndrome can be identified by modifying the patient's baseline risk according to the results of the ultrasound. The second trimester scan will likely continue to play an important role in the future in the detection of aneuploidy.