Uptake rate of prenatal genetic screening and invasive testing in pregnant women over the age of 37 in Tygerberg Hospital and factors influencing this.
Date
2021-12
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Abstract
Introduction
Prenatal screening in pregnant women of advanced maternal age has been shown to be ineffective in
Cape Town. This study aims to determine the uptake rate of prenatal screening and invasive testing by
pregnant women over the age of 37 at conception referred to the Tygerberg Hospital fetal medicine
unit in 2016, as well as factors which influence this.
Methods
A retrospective audit was done of prospectively collected data from women over 37. According to our
protocol, invasive testing was offered for either age over than 40 years at conception, a high
ultrasound‐based risk or a fetal anomaly on ultrasound. Termination of pregnancy was offered for
severe structural anomalies or confirmed genetic disorders.
Results
Of 1196 older women, 645 (54%) received formal genetic counselling and 640 (53.5%) were offered
invasive testing. Only 114 (9.5% of all) underwent invasive genetic testing for an overall prenatal
testing uptake rate of 17.8%. An additional 10 patients opted for termination of pregnancy without
invasive testing but 80% of women who were offered invasive genetic testing (according to our
protocol) declined this. Women older than 40 years at conception (75.8 vs 59.6%), those who had
previous first trimester losses and those who received pre‐screen counselling (21.2% vs 7.9%) were
more likely to decline invasive testing. A higher adjusted risk and a less favourable risk adjustment had
a significant effect on the acceptance rate of testing in both first and second trimester assessments
and acceptance were highest when a fetal anomaly was detected (54%). Risk reduction was most
effective in the first trimester (92% becoming low risk) than after only second trimester assessment
(64 % becoming low risk) but most assessments were done and most aneuploidies and anomalies were
detected in the second trimester. Diagnostic yield for chromosomal abnormalities was 15.8% (18/114).
Conclusions
Uptake of invasive testing in this study was low (17.8%), and lower than seen in previous years. Uptake
rate was somewhat influenced by maternal characteristics (age, previous miscarriage) and somewhat
by the ultrasound‐based risk result, but more so by the offer of pre‐screen counselling and
predominantly by the women’s pre‐existing attitude towards the service, Trisomy 21 or the option of
termination of pregnancy.
Efforts should focus on pre‐screen counselling and first trimester ultrasound screening to improve the
cost effectiveness of our prenatal genetic screening program for women of advanced maternal age,
but the second trimester ultrasound screening remains paramount as it still provides sensitive
aneuploidy screening (although less effective than in the first trimester) for women who initiate
antenatal care or are referred after the first trimester and allows the detection of more fetal anomalies
than in the first trimester. Pre‐screen counselling and first trimester ultrasound assessment should be
improved to dramatically improve the prenatal genetic screening service.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar
Description
Thesis (MMed)--Stellenbosch University, 2021.
Keywords
Genetic screening, Prenatal care, Pregnant women -- Invasive testing