9.3 Prenatal diagnostics

• Introductory remarks
  
• Non-invasive methods
  
  • Ultrasound as the standard
    
  • The times for ultrasound examinations
    
  • Symphysis-fundus uteri distance
  • Cardiotocogram (CTG)
• Invasive methods
  
  • Chorion biopsy
  • Amniocentesis
  • Umbilical blood sampling
• Prenatal therapy
  • Fetal surgery
  • Prophylaxy
  • Gene therapy
  • Medical therapy

The times for ultrasound examinations

The first ultrasound examination is made at the beginning of the fetal period, i.e., in the 8th –10th week of pregnancy (WoP: 10 – 12 weeks after the LMP). Normally, it is made trans-abdominally, but in case of maternal obesity or a retroverted uterus it can also be made trans-vaginally.

Fig. 10
In this picture, a fetus at the end of the embryonic period is shown in a median sagittal section. This image is suitable for determining the crown-rump length of the fetus.
In practice, the doctor utilizes checklists so that no parameter is overlooked.

The second ultrasound examination takes place in the 18th – 21rst WoP (20 – 23 weeks after the LMP). Normally, in the second and third trimenon the examinations are performed trans-abdominally.

The main aim of this examination lies in adjudging the fetal anatomy. With fetometry it is possible either to display fetal malformations directly or detect them due to indirect clues. At the same time, the volume of the amniotic fluid and the position and morphology of the placenta are gauged.

In high-risk pregnancies and with unclear findings, supplementary ultrasound examinations are indicated.