Department of Obstetrics and Gynaecology, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa, Panorama Perinatology, Mediclinic Panorama, Cape Town, South Africa.
Department of Obstetrics and Gynaecology, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa.
S Afr Med J. 2023 Nov 6;113(11):27-34. doi: 10.7196/SAMJ.2023.v113i11.885.
Screening for trisomy 21 provides pregnant women with accurate risk information. Different algorithms are used to screen for trisomy 21 in South Africa (SA). The Fetal Medicine Foundation (FMF) provides software to screen for trisomy 21 in the first trimester by ultrasound or a combination of ultrasound and biochemistry (combined screening), and requires regular and stringent quality control. With αlpha software, first trimester combined screening and screening with biochemistry alone in the first or second trimester are possible. The αlpha screening requires quality control of biochemical tests, but not of ultrasound measurements. Ideally, a screening test should have a high detection and a low screen positive rate. Despite the availability of these screening programmes, only a minority of infants with trisomy 21 are detected prenatally, raising questions about the effectiveness of screening.
To determine the screen positive and detection rates of prenatal screening for trisomy 21 in the SA private healthcare system.
Data from the three largest laboratories collected between 2010 and 2015 were linked with genetic tests to assess screen positive and detection rates. Biochemical screening alone with αlpha software (first or second trimester) and combined screening using either FMF or αlpha software were compared.
One-third of an estimated 675 000 pregnancies in private practice in the 6-year study period underwent screening. There were 687 cases of trisomy 21 in 225 021 pregnancies, with only 239 (35%) diagnosed prenatally. The screen positive rates were 11.8% for first trimester biochemistry, 7.6% for second trimester biochemistry, 7.3% for first trimester FMF software ultrasound alone, 3.7% for combined first trimester screening with FMF software, and 3.5% for combined first trimester screening with αlpha software. The detection rates for a 5% false positive rate were 63% for first trimester biochemistry, 69% for second trimester biochemistry, 95% for combined first trimester screening with FMF software and 80% for combined first trimester screening with αlpha software. Detection and confirmation rates were highest with FMF software.
Screening with FMF software has a similar screen positive rate and better detection rate than screening with αlpha software. The low prenatal detection rate of trisomy 21 is mainly due to a low prevalence of screening. More research is needed in the SA setting to explore why screening and confirmatory testing after high-risk results are not performed in many pregnancies.
筛查 21 三体可以为孕妇提供准确的风险信息。南非（SA）使用不同的算法来筛查 21 三体。胎儿医学基金会（FMF）提供软件来通过超声或超声和生化联合（联合筛查）筛查 21 三体，并要求定期进行严格的质量控制。使用 αlpha 软件，可以进行早孕期联合筛查以及早孕期或中孕期单独进行生化筛查。αlpha 筛查需要对生化检测进行质量控制，但不需要对超声测量进行质量控制。理想情况下，筛查试验应该具有较高的检出率和较低的筛查阳性率。尽管有这些筛查方案，但只有少数 21 三体患儿在产前被发现，这引发了对筛查有效性的质疑。
确定南非私人医疗保健系统中 21 三体产前筛查的筛查阳性率和检出率。
将 2010 年至 2015 年间三家最大的实验室收集的数据与基因检测结果进行关联，以评估筛查阳性率和检出率。比较单独使用 αlpha 软件进行生化筛查（早孕期或中孕期）和使用 FMF 或 αlpha 软件进行联合筛查。
在 6 年的研究期间，估计有 675 000 例私人执业的妊娠中，有 1/3 接受了筛查。在 225 021 例妊娠中，有 687 例 21 三体，仅有 239 例（35%）在产前诊断。早孕期生化筛查的筛查阳性率为 11.8%，中孕期生化筛查为 7.6%，早孕期 FMF 软件超声检查为 7.3%，早孕期联合 FMF 软件筛查为 3.7%，早孕期联合 αlpha 软件筛查为 3.5%。假阳性率为 5%时的检出率为早孕期生化筛查为 63%，中孕期生化筛查为 69%，早孕期联合 FMF 软件筛查为 95%，早孕期联合 αlpha 软件筛查为 80%。FMF 软件的检测和确认率最高。
与 αlpha 软件相比，使用 FMF 软件进行筛查具有相似的筛查阳性率和更好的检出率。21 三体的产前检出率低主要是由于筛查的患病率低。在南非，需要进行更多的研究来探索为什么在许多妊娠中，即使存在高风险结果，也不进行筛查和确认性检测。
