AFJOG

GUIDELINES Ultrasound markers are conversely more important. 17 Some laboratories would not use biochemistry for risk calculation in multiple pregnancies, and only use the ultrasound parameters. The complexities of screening and diagnosis in multiple pregnancies are such that the input of a fetal specialist is invaluable. 18 NIPT is accurate in twin pregnancies, 19 but preference should also be given to NIPT based on single nucleotide polymorphism (SNP) testing. SNP based NIPT can determine the zygosity and calculates a fetal DNA fraction for each fetus separately. 12 Further diagnostic testing depends on determining which fetus (in case of dichorionic twins) is affected, for which advanced ultrasound and detailed counselling is required. 18 10. If the pregnancy is in the second trimester, with a singleton fetus without obvious abnormalities and the patient opts against NIPT, offer second trimester screening for common autosomal trisomies by means of the triple test (maternal serum alpha-foetoprotein [MS-AFP], unconjugated estriol [uE3] and total human chorionic gonadotropin [HCG]) or the quadruple test (MS-AFP, uE3, HCG and dimeric inhibin A) (second trimester biochemistry screening). Second trimester biochemistry screeninghas a lower detection of trisomy 21 than first trimester screening. 4 The quadruple test has a higher sensitivity for a similar screen positive rate compared to the triple test 20 and should be the test of preference,dependingonavailability,ratherthanthetripletest. 11. If an intermediate risk for trisomies is found (between 1:301 and 1:1000 by first trimester screening or between 1:271 and 1:1000 by second trimester biochemistry screening), the patient should be offered NIPT. An alternative to NIPT would be an advanced ultrasound (“genetic sonogram”) performed at mid gestation (18 – 22 weeks). 21 Although the detection of chromosomal anomalies using this approach is highly dependent on the expertise of the practitioner, it has been shown to be effective even in a low-cost setting. 22 If neither of these is a feasible option for the patient, this should be noted, and she should be managed as a patient at low risk of a common chromosomal anomaly. 12. If NIPT or FMF-cFTS demonstrates a high risk of a fetal chromosomal anomaly, the patient should be referred for genetic counselling and possible invasive testing. 13. If the risk for common autosomal trisomies based on second trimester biochemistry screening is between 1:2 and 1:270 (“high risk”), the patient should be referred for genetic counselling and offered invasive testing. 14. If a low risk for common autosomal trisomies is found on first or second trimester biochemistry or FMF-cFTS screening (between 1:1001 and 1:9999), or with NIPT, the patient should be offered or referred for a second trimester detailed ultrasound at mid-gestation (18 to 22 weeks) as screening for fetal structural anomalies. 15. If a patient declines a detailed anatomical fetal ultrasound evaluation because she does not want to know about any possible fetal anomalies, a basic ultrasound should be offered at mid gestation to obtain information of obstetric value only. The patient should be aware that while some abnormalities may be detected on a basic scan, this is not its primary purpose and the majority of genetic or structural abnormalities would not be detected. 16. If a patient declines a detailed anatomical fetal ultrasound evaluation for financial reasons, MS-AFP levels should be measured between 15 and 20 weeks (if not already done as part of second trimester biochemistry screening). Second trimester MS-AFP screening can detect 95% of cases of anencephaly, and 80% of cases of open spina bifida. 23 If the MS-AFP is raised (more than 2 multiples of the median [MoM] or classified as “high risk”), the patient should be informed of the possible causes and referred for advanced ultrasound examination. 17. If a patient opts for a detailed anatomical fetal ultrasound evaluation, the risk of a fetal abnormality should be assessed. If there is an increased risk for a fetal anomaly, or if an anomaly is found on detailed or basic ultrasound, the patient should be referred for advanced ultrasound, including fetal echocardiography 24 or fetal neurosonography 25 as appropriate.(Table 2). Table 2. Indications for advanced fetal ultrasound examination Family history of, or previous pregnancy with inheritable malformation Maternal diabetes or other metabolic diseases (e.g. phenylketonuria) Maternal exposure to teratogens (environmental, pharmaceutical or recreational) Maternal antibodies (anti-Ro/SSA, anti-thyroid, anti-red cell, anti-platelet) Conception by IVF, including ICSI Monochorionic twins Visibly enlarged nuchal translucency or cystic hygroma Suspected or confirmed congenital intrauterine infection Suspected or confirmed fetal structural anomaly or hydrops Fetal cardiac rate or rhythm disturbances (Persistent bradycardia / tachycardia /irregular heart rhythm)Confirmed or suspected genetic abnormality (including whole exome sequence or microarray findings of uncertain significance) (modified from references (24,25) Conclusion This document has been developed by interdisciplinary healthcare teams utilizing the best available evidence and resources believed to be accurate and current at the time of press. These guidelines are an attempt to standardize and improve the equality of the discussion and offering of prenatal screening in private practice in South Africa, while taking into account the disparity of resources available to different patients. The guidelines should not be solely relied on or used as a substitute for assessing the individual needs of each patient, and should be read with the attached flowcharts (Figure 1 and 2) for singleton and multiple pregnancies. Acknowledgements We would like to thank dr Graham Howarth and dr Bettina Taylor for their critical review of the manuscript. African Journal of Obstetrics and Gynaecology | Volume 1 | Issue 2 | 2023 | 29