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

Introductory remarks

Today there are various possibilities for examining the embryo and fetus. This prenatal diagnostic is a special area of genetic counseling. One differentiates between non-invasive and invasive examination methods.
With invasive methods there is always the risk of injuring the fetus, and thus provoking an abortion or a miscarriage. Such an examination is always called for, though, when a risk exists for a definite genetic ailment that can be detected either in the cells, in the amniotic fluid, in the blood, or in the morphology of the fetus.
Prenatal diagnostic examination can only take place following a comprehensive explanation and counseling of parents that must be documented. In these, ethic/moral as well as legal aspects must be considered. The goal should be to find solutions with the parents in which responsible decisions according to the best knowledge and conscience can be made.

Non-invasive methods

Among today's non-invasive methods for prenatal diagnostics ultrasound stands at first place. Further possibilities, especially in advanced stages of the pregnancy and at the time of delivery, consist in the symphysis-fundus uteri distance (SFD) as well as the cardiotocography (simultaneous recording of infantile heart beats and maternal labor activity). Moreover, the first infantile movements, with those giving birth for the first time (primipara) after the 18th week (20th week after the LMP), with those giving birth again (pluripara) after the 16th week (18th week after the LMP), can yield a surprisingly precise due-date.

Ultrasound as the standard

Like no other method an ultrasound examination makes it possible to obtain information - non-invasively - about the gestation age and thus about the upcoming date of birth, as well as about the intactness of the gravidity.

The ultrasound examination primarily serves embryo/ fetometry. In the initial ultrasound examination, one attempts to ascertain as precisely as possible the date of birth. As a first sign of an incipient pregnancy an echo-yielding zone only a few mm in diameter is thereby visible shortly after the implantation.

Fig. 7
An echo-yielding zone of a few millimeters indicates an incipient pregnancy.
This picture shows the young embryo shortly after the implantation.

Fig. 8
Ultrasound image from a triplet pregnancy in the 11th week.

As the further development continues, the first heartbeats, fetal movements and the long bones of the skeleton can soon be observed. In the 10th to 12th week of pregnancy (WoP) the cartilage formation of the skull is so advanced that the biparietal diameter (BPD) of the head and the femoral length (FE) provide important evidence for determining the further duration of the pregnancy.

Fig. 9
With the aid of growth curves the temporal status of the pregnancy can be determined. For example, one measures the biparietal diameter (BPD) or the femoral length (FE) of the fetus. Here are depicted the 50th percentile (middle BPD and FE lines) as well as the upper and lower boundaries, where 90% of the values normally measured are to be found. Measurements should always lie more or less along the same line. A large change, e.g., a jump from the 20th to the 95th percentile can be a clue that a pathologic event has occurred.