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
Catalogue details

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.

    26/80 (page 18)
    Methods of prenatal diagnosis Amniocentesis Fig 7. Fall in the birth-rate or infants with thalassaemia major associated with several thalassaemia control programmes [32]. Table 7. Present fetal sampling procedures, risks and time required to obtain a diagnosis Obstetric aspects Time to diagnosis Sampling procedure Weeks’ gestation Risk to pregnancy (%) Karyotyping Culture Rapid Biochemistry Culture Direct DNA Culture Direct Amniocentesis 14-17 0.5-1 2^4wk — 2-4wk — 5wk >10d a Fetal blood sampling >18 1-7 — 3d — 2-7d lOd Chorionic villus sampling >9 2-4 2wk 2d 2wk Id lOd Ultrasound ~ 9 + b Time to a definitive ultrasound diagnosis depends on many variables. Rapid karyotyping may be required. a New DNA methods promise to reduce the time to diagnosis to 1-2 days. b The risk is of false positive diagnosis leading to abortion of a healthy fetus. 2.33 Present methods of obtaining fetal material for analysis, with their advan tages and disadvantages, are listed in Table 7. 2.34 Amniocentesis should be carried out under real-time ultrasound guidance by an experienced obstetrician. It is usually carried out at around 16 weeks of pregnancy and although it is a relatively simple technique, it continues to evolve, with better ultrasound monitoring and the use of disposable needles. 2.35 There is still some uncertainty about the exact risk to the pregnancy from amniocentesis [15] largely because the risk is so low that it is extremely difficult to measure. The best studies suggest a 1% excess risk of spontaneous abortion following amniocentesis and a slightly increased incidence of mild respiratory problems in the newborn. One study suggested an increased incidence of club-foot,