Prenatal diagnosis and genetic screening : community and service implications / a report of the Royal College of Physicians.

  • Royal College of Physicians of London.
Date:
1989
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Prenatal diagnosis and genetic screening : community and service implications / a report of the Royal College of Physicians. Source: Wellcome Collection.

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    Summary 2.46 However, even with the best standard of practice it is not possible at present, and probably never will be possible, to complete all prenatal diagnoses before the 20th week of gestation. The reasons for this are as follows: i Because the organ-systems must be adequately developed before abnormalities can be seen, many congenital malformations cannot be diagnosed before the 19th week of gestation. ii Some diagnoses (eg of fetal infections and immune deficiencies) depend on measuring products of the fetal immune system. Since the fetal immune system is not always functional before 20 weeks’ gestation, these diagnoses cannot be made before this stage. iii W omen are sometimes slow to recognise that they are pregnant, or may present relatively late at the antenatal clinic. The high-risk ones among them will therefore be recognised relatively late. iv Even with early recognition of risk and early fetal sampling, laboratory diagnosis sometimes takes several weeks. 2.47 As a rule, prenatal diagnosis can be completed by 24 weeks of pregnancy. Pressure to complete all prenatal diagnoses earlier, eg before 20 weeks of pregnancy, would exclude many people who need it and would lead to inequity in service delivery. The pressure generated would also militate against the high standard of practice recommended at the beginning of this chapter and would lead to avoidable errors. 52.1 Although it will never be possible to identify everyone at risk, with present technology the potential exists for a great reduction in births of infants with severe congenital and genetically determined disorders. 52.2 Prenatal diagnosis involves an invasion of many seemingly normal preg nancies in the search for uncommon abnormalities, and so must be practised to the highest possible standard. 52.3 Existing evidence indicates that with an appropriate obstetric ultrasound service, many major congenital malformations can be detected during the second trimester of pregnancy. 52.4 Obstetric ultrasound and its applications are important parts of the emerging sub-specialty of fetal medicine. Obstetric ultrasound is an integral part of good obstetric care at all levels, and full information, advice and support, and rapid obstetric back-up must be available on the spot. Expert fetal medicine centres should be associated with clinical genetics centres. 52.5 If all mothers over 35 were to undergo fetal karyotyping and consequent selective abortion, the birth-rate of infants with severe chromosomal abnormalities would be reduced by only 35%. Better methods of primary screening to predict more accurately the presence of a fetus with Down’s syndrome are described in Chapter 3. 52.6 Developments in DNA analysis are constantly increasing the range and accuracy of prenatal and carrier diagnosis for inherited diseases, and can be used at any stage of embryonic development. Since prenatal diagnosis using DNA often depends on analysing DNA from an affected relative, it is now essential to obtain and store DNA from individuals with major inherited diseases, for the future benefit of other family members.