9.3 Prenatal diagnostics

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 - Length display of an embryo  Legend

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.

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With the first ultrasound examination the following questions are answered:

  • Excluding uterine abnormalities and genital tumors
  • Location of the Implantation
  • Number of fetuses
  • Vitality of the fetus
  • Checking the gestation age by measuring the crown-rump length
  • Measuring the fetal neck edema
  • Checking the body form (head, rump, extremities)


Quiz 04


Quiz 07

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.

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Also in the second ultrasound examination the development of the fetus is established with various parameters:

  • Biparietal diameter
  • Femoral length
  • Abdominal diameter
  • Amniotic fluid volume determination: fetus: fluid = 1:1 = normal
  • Position and morphology of the placenta

A diminished or augmented volume of amniotic fluid is frequently associated with fetal abnormalities and chromosomal aberrations.

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

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