Aneuploidy screening in women of advanced age in the public healthcare setting of a low- to middle- income country - an observational cohort study.

BACKGROUND

Screening and termination of pregnancy (TOP) for Down syndrome (DS) are both available in South Africa (SA), but DS is infrequently diagnosed prenatally in the public sector (7% in 2008), resulting in a high live-birth prevalence (1.33 - 2.1 per 1 000). In the SA public sector, DS screening and confirmatory genetic testing are fully state subsidised for women of advanced maternal age (AMA) but, owing to the low positive predictive value of AMA-based screening, ultrasound-based screening is also offered. Given the limited resources and the steady increase in the number of pregnant women of AMA, the value of DS screening in altering pregnancy outcome needs to be critically assessed.

OBJECTIVES

To determine the uptake of prenatal screening for DS, invasive testing and TOP in pregnant women of AMA, as well as factors influencing maternal decisions.

METHODS

This retrospective cohort study, based on prospectively captured data, includes all women of AMA (>37 years at conception) seen at a regional fetal medicine unit in Cape Town offering fully state subsidised DS screening and testing for a geographically defined area, including mostly women of African or mixed ancestry. Screening was age- and ultrasound-based, and DS risks were calculated using published algorithms. Non-directive genetic counselling was provided to all women ≥40 years old (pre-screen if feasible), women with a relevant history, a fetal anomaly or DS risk higher than that of a woman aged 37 years. Participant characteristics, results, decisions and reasons to decline testing were recorded prospectively, and compared between women <40 completed years and ≥40 years old, and between women accepting or declining invasive testing or TOP.

RESULTS

During the study period, 1 196 women of AMA were seen. Ninety-three received pre-screen counselling, and 44 of these declined DS screening (47.3% (95% confidence interval (CI) 36.9 - 57.9)). Uptake of invasive testing after screening was low (18.1% (CI 15.2 - 21.3)). Age category was not an independent confounder for this, but uptake was lower after previous miscarriage(s), higher after high-risk screening results and highest with a fetal anomaly. The most common reason for declining testing was opposition to TOP. The uptake of TOP for DS, when offered to those who were screened and had accepted invasive testing, was 65.8% (48.7 - 80.4).

CONCLUSION

The uptake of screening and/or testing was low, and this reflected strong views on TOP for DS. As uptake of testing and/or TOP was higher with abnormal ultrasound findings, a prenatal screening programme addressing structural anomalies and aneuploidies simultaneously (i.e. ultrasound) is preferred over other DS screening tools that target DS specifically.