Inaccurate estimation of risk in second trimester serum screening for Down syndrome among women who have already had first trimester screening

Uptake of prenatal diagnostic testing and the effectiveness of prenatal screening for Down syndrome

OBJECTIVES

To map prenatal screening and diagnostic testing pathways in Victorian pregnant women during 2003 to 2004; measure the impact of prenatal diagnostic testing uptake on the effectiveness of prenatal screening for Down syndrome; and assess factors influencing uptake of diagnostic testing following screening.

METHODS

State-wide data collections of prenatal screening and diagnostic tests were linked to all Victorian births and pregnancy terminations for birth defects.

RESULTS

Overall, 52% of women had a prenatal test (65 692/126 305); screening (44.9%), diagnostic testing (3.9%), or both (3.2%). Uptake of diagnostic testing was 71.4% (2390/3349) after an increased risk screen result, and 2.5% (1381/54 286) after a low risk result. Variation in uptake of diagnostic testing reduced the effectiveness of the screening program by 11.2%: from 87.4% (sensitivity - 125/143) to 76.2% (prenatal diagnoses of Down syndrome - 109/143). In both the increased and low risk groups, uptake was influenced by absolute numerical risk, as well as by the change in numerical risk from a priori risk.

CONCLUSIONS

This comprehensive follow-up demonstrates clearly that numerical risk is being used to aid in decision making about confirmatory diagnostic testing. Collectively, these fundamental individual decisions will impact on the overall effectiveness of screening programmes for Down syndrome.

Preimplantation genetic screening as an alternative to prenatal testing for Down syndrome: preferences of women undergoing in vitro fertilization/intracytoplasmic sperm injection treatment

OBJECTIVE

Although the primary goal of preimplantation genetic screening (PGS) is to increase pregnancy rates in women undergoing IVF/intracytoplasmic sperm injection treatment, it has been suggested that it may also be used as an alternative to prenatal testing for Down syndrome.

DESIGN

Trade-off questionnaires.

SETTING

Two university centers for reproductive medicine.

PATIENT(S)

Two hundred forty-four subfertile women.

INTERVENTION(S)

Scenarios with different pregnancy chances after PGS and with different risk reductions of a Down syndrome pregnancy were presented.

MAIN OUTCOME MEASURE(S)

Willingness to have PGS performed in the various scenarios.

RESULT(S)

In case PGS would discover all Down syndrome embryos without affecting pregnancy chances, 83% of the women would have PGS performed. If PGS lowered pregnancy chances from one in five to one in seven, 36% of the women preferred to have PGS performed. If PGS reduced the chance of a Down syndrome pregnancy with 80% without affecting pregnancy chances, 75% of the women would have PGS performed, and 31% of them would refrain from prenatal testing afterward.

CONCLUSION(S)

Most women favor PGS for Down syndrome screening, even if it is not 100% sensitive. The acceptability depends on the effect PGS has on pregnancy chances, and, to a lower extent on its sensitivity to detect Down syndrome embryos.

Dépistage de la trisomie 21 par le test combiné du premier trimestre suivi par l'échographie du second trimestre en population générale

BACKGROUND

Recent studies have reported the efficacy of first trimester combined screening for Down Syndrome based on maternal age, serum markers (human chorionic gonadotropin, pregnancy-associated plasma protein A), and ultrasound measurement of fetal nuchal translucency. However, those do not incorporate the value of the widely accepted routine 20-22 week anomaly scan.

STUDY DESIGN

We carried out a multi-centre, interventional study in the unselected population of a single health authority in order to assess the performance of first trimester combined screening, followed by routine second trimester ultrasound examination and/or screening by maternal serum markers (free beta-hCG and alpha-fetoprotein measurement or total hCG, alpha-fetoprotein and unconjugated estriol measurement) when incidentally performed. Detection and screen positive rates were estimated using a correction method for non verified issues. A cost analysis was also performed.

RESULTS

During the study period, 14,934 women were included. Fifty-one cases of Down Syndrome were observed, giving a prevalence of 3.4 per 1000 pregnancies. Of these, 46 were diagnosed through first (N=41) or second (N=5) trimester screening. Among the 5 screen-negative Down syndrome cases, all were diagnosed postnatally after an uneventful pregnancy. Detection and screen positive rates of first trimester combined screening were 79.6% and 2.7%, respectively. These features reached 89.7 and 4.2%, respectively when combined with second trimester ultrasound screening. The average cost of the full screening procedure was 108 euro (120 $) per woman and the cost per diagnosed Down syndrome pregnancy was 7,118 euro (7,909 $).

CONCLUSION

Our findings suggest that one pragmatic interventional two-step approach using first-trimester combined screening followed by second trimester detailed ultrasound examination is a suitable and acceptable option for Down syndrome screening in pregnancy.

Screening for Down syndrome using first-trimester combined screening followed by second-trimester ultrasound examination in an unselected population

OBJECTIVE

Recent studies have reported the efficacy of first-trimester combined screening for Down syndrome based on maternal age, serum markers (human chorionic gonadotropin, pregnancy-associated plasma protein A), and ultrasound measurement of fetal nuchal translucency. However, those do not incorporate the value of the widely accepted routine 20-22 weeks' anomaly scan.

STUDY DESIGN

We carried out a multicenter, interventional study in the unselected population of a single health authority in order to assess the performance of first-trimester combined screening, followed by routine second trimester ultrasound examination and/or screening by maternal serum markers (free beta-hCG and alpha-fetoprotein measurement or total hCG, alpha-fetoprotein, and unconjugated estriol measurement) when incidentally performed. Detection and screen positive rates were estimated using a correction method for nonverified issues. A cost analysis was also performed.

RESULTS

During the study period, 14,934 women were included. Fifty-one cases of Down syndrome were observed, giving a prevalence of 3.4 per 1000 pregnancies. Of these, 46 were diagnosed through first (n = 41) or second (n = 5) trimester screening. Among the 5 screen-negative Down syndrome cases, all were diagnosed postnatally after an uneventful pregnancy. Detection and screen positive rates of first-trimester combined screening were 79.6% and 2.7%, respectively. These features reached 89.7%, and 4.2%, respectively, when combined with second-trimester ultrasound screening. The average cost of the full screening procedure was 108 euros (120 dollars) per woman and the cost per diagnosed Down syndrome pregnancy was 7,118 euros (7909 dollars).

CONCLUSION

Our findings suggest that 1 pragmatic interventional 2-step approach using first-trimester combined screening followed by second-trimester detailed ultrasound examination is a suitable and acceptable option for Down syndrome screening in pregnancy.

Patient preference regarding first-trimester aneuploidy risk assessment

OBJECTIVE

We assessed patient views regarding disclosure of first-trimester Down syndrome risk assessment results compared with withholding results until a single, more accurate second-trimester screening result is available.

STUDY DESIGN

A prospective, institutional review board-approved, voluntary, anonymous survey was presented to patients with singleton pregnancies who were undergoing first-trimester nuchal translucency and biochemical screening at our institution. Options included immediate (sequential testing) or later disclosure (integrated testing). Descriptions and a comparison of the options were included in the survey.

RESULTS

One hundred one women completed the questionnaires; 69.3% of the patients preferred sequential testing, compared with 30.7% of the patients who were either unsure or preferred integrated testing. Older patients and those patients with better background knowledge of screening tests preferred earlier disclosure of screening results (P = .035 and P = .026, respectively). Patients who preferred earlier disclosure also preferred termination of a Down syndrome pregnancy (P = .013).

CONCLUSION

Older patients and those patients with a better understanding of screening tests preferred immediate disclosure of first-trimester risk assessment results; these women were more likely to prefer to terminate an affected pregnancy.

Evaluation of Down syndrome screening strategies

Women contemplating pregnancy today have many different Down syndrome screening protocols from which to choose. Sensitive and specific first and second trimester screening protocols are now widely available, and strategies that combine first and second trimester markers are moving from investigational use into the clinical arena. Modeling indicates that a high detection rate (85%) associated with a very low screen positive rate (1.3%) can be achieved with contingent screening, in which all women undergo first trimester screening and only a portion (25%) go on to second trimester screening.

First trimester Down syndrome screening: public health implications

Down syndrome (DS) screening has been an integral part of routine prenatal screening for the last three decades. Recent efforts have been directed at developing additional non-invasive prenatal screening techniques that could not only improve sensitivity of prenatal screening, but also be employed in the first trimester to offer earlier diagnostic and interventional opportunities. Nuchal translucency has proven to be an effective and cost-effective screening test that, when combined with serum markers (hCG and pregnancy-associated plasma protein [PAPP-A]) in the first and/or second trimester, broadens the diagnostic possibilities and improves the diagnostic capabilities of current prenatal DS screening methods. Despite the potential benefits, significant operational issues regarding access to and availability of such testing may limit its widespread application and necessitates the maintenance of both non-sonographic and second trimester screening methods. The implementation of first trimester DS testing requires the development and maintenance of nationally standardized quality control systems to ensure the reliability of serum and ultrasound measurements and the accurate assessment of risk. Future efforts to improve prenatal screening should continue to emphasize the need for improved access to all aspects of prenatal care, stress the importance of provider education and the necessity for extensive patient counseling, and reinforce the role of patient education and choice.

First-trimester screening for aneuploidy

Prenatal screening for aneuploidy in the first trimester using novel ultrasound and maternal serum markers represents a promising improvement over the currently available second-trimester screening methods. This article reviews the current status of first-trimester screening for Down syndrome and other aneuploidies and explores the issues related to implementing first-trimester screening into mainstream prenatal care in the United States.

Screening for trisomy 21 in Flanders: a 10 years review of 40.490 pregnancies screened by maternal serum

OBJECTIVE

To evaluate maternal serum screening for trisomy 21 (MSS) in Flanders between 1992 and 2002.

STUDY DESIGN

Data of a large database on the results of MSS, nuchal translucency (NT) and pregnancy outcome were analysed retrospectively.

RESULTS

Despite an excellent performance of second trimester MSS at a maternal age > or = 35 years (94.4% detection rate (DR) of trisomy 21 at a false positive rate (FPR) of 22.4%), the proportion of patients above 35 years of age in the study population was significantly lower than in the Flemish general pregnant population (5.5% versus 8.9%, P < 0.001). In the population screened by MSS and NT, the DR of second trimester MSS at a 5% FPR was 44.4%, which was lower than 66.6% in the population screened by MSS without NT. When nine trisomy 21-affected pregnancies were compared to 3265 normal pregnancies, the mean NT-MoM values were not significantly different (1.16 +/- 0.89 versus 1.00 +/- 0.46, P > 0.05). Both the findings comply to a sequential screening practice where second trimester MSS is only performed after a normal measurement of NT in the first trimester.

CONCLUSION

In Flanders, the uptake of second trimester maternal serum screening is low in women aged 35 years or more. Its screening performance decreased after the introduction of sequential screening.

Screening for aneuploidy in twins and higher-order multiples: is first-trimester nuchal translucency the solution?

Screening for aneuploidy in twins and higher-order multiples present complex practical and ethical issues that limit its provision to women. We review the currently available screening options and compare the merits and disadvantages of each method. The available diagnostic tests and therapeutic interventions for screen positive cases are also reviewed.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to list the various screenings for Down syndrome during pregnancy, to outline the advantages and disadvantages of each screening method, and to summarize the challenges in screening for aneuploidy in twins.

Advances in prenatal screening for Down syndrome: II first trimester testing, integrated testing, and future directions

BACKGROUND

The acceptability of prenatal screening and diagnosis of Down syndrome is dependent, in part, on the gestational age at which the testing is offered. First trimester screening could be advantageous if it has sufficient efficacy and can be effectively delivered.

ISSUES

Two first trimester maternal serum screening markers, pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (beta-hCG), are useful for identifying women at increased risk for fetal Down syndrome. In addition, measurement of an enlarged thickness of the subcutaneous fluid-filled space at the back of the neck of the developing fetus (referred to as nuchal translucency or NT) has been demonstrated to be an indicator for these high-risk pregnancies. When these three parameters are combined, estimates for Down syndrome efficacy exceed those currently attainable in the second trimester. Women who are screen-positive in the first trimester can elect to receive cytogenetic testing of a chorionic villus biopsy. The first trimester tests could also, theoretically, be combined with the second trimester maternal serum screening tests (integrated screening) to obtain even higher levels of efficacy. There are, however, several practical limitations to first trimester and integrated screening. These include scheduling of testing within relatively narrow gestational age intervals, availability of appropriately trained ultrasonographers for NT measurement, risks associated with chorionic villus biopsy, and costs. There is also increasing evidence that an enlarged NT measurement is indicative of a high risk for spontaneous abortion and for fetal abnormalities that are not detectable by cytogenetic analysis. Women whose fetuses show enlarged NT, therefore, need first trimester counseling regarding their Down syndrome risks and the possibility of other adverse pregnancy outcomes. Follow-up ultrasound and fetal echocardiography in the second trimester are also indicated.

CONCLUSION

First trimester screening appears to be a highly effective method to screen for Down syndrome. Women with screen-positive results based on NT measurement appear to be at increased risk for diverse fetal abnormalities. The finding of a normal fetal karyotype may not, therefore, carry a high level of reassurance for a normal baby.

[Alternatives to amniocentesis for maternal age]

Screening strategies of Down's syndrome should be re-evaluated. Amniocentesis for advanced maternal age has been proposed in the 70's because no other screening test was available. Maternal serum screening and first trimester nuchal translucency are now well validated, including in women over 38. The sequential and independent use of different screening tests leads to a dramatic increase of the false positive rate and thus of iatrogenic fetal losses. Maternal age remains the major risk factor for chromosomal anomalies, but it should be included in risk calculation strategies (ideally combining serum screening and nuchal translucency), and not taken as an isolated information. These screening strategies require strict quality control and audit, which is currently better achieved with serum screening than ultrasound screening. A complete information about Down's syndrome screening strategies should be given to women, regardless of their age, and their personal choice should be respected. For women of advanced maternal age, a policy of selective rather than routine amniocentesis is likely to reduce the risk of iatrogenic fetal loss and yet to allow for a reasonable sensitivity.