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.
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.
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.
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.
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.
Symphysis-fundus uteri distance
Since in the last trimenon no ultrasound examination is routinely used, when some sort of growth disturbance is suspected, the diagnosis must be made with the aid of clinical means and these must be performed at the right time. The measurement of the symphysis-fundus uteri distance (SFD) according to Westin has proved to be the best clinical standard. This extent approximates the crown-rump length of the fetus.
For this reason, during the examination in the second trimenon, the SFD is determined when the second ultrasound examination is made and recorded on the standard curve. At each further pregnancy check-up, the SFD is documented in the same way. If it clearly deviates from the percentile band, this can be interpreted as a sign of a fetal growth disorder. In such cases a supplementary ultrasound examination in the 3rd trimenon for adjudging the fetal growth is indicated.
During birth a continuous observation of the child is attempted in order to recognize a danger to the child at the right time. The cardiotocogram is an ideal method for this and consists in a continuous derivation and recording of the fetal heartbeat frequency together with the contraction activity of the uterus during the delivery. In this way, an intrauterine hypoxia can be detected early.