Fetal anatomy screening

The screening for congenital abnormalities is one of the most important ultrasound scans during pregnancy. The given examinations is performed with the help of the abdominal probe during pregnancy weeks 20-21. At this stage of pregnancy the fetus has all organs developed and it faces the growth and maturing period. During pregnancy week 20 about half of pregnancy has passed and half is still ahead. The fetus weighs 300-350 g during this period and its length is 21-22 cm. The fetus already resembles the human being, but it cannot yet smile, as the mimic muscles of its face have not yet fully developed.

The fetus already opens its mouth and swallows and breaths amniotic fluid, feeling its smell and taste. The inner ear of the fetus has already fully developed, so that it can hear the sounds coming from the uterus: heartbeat of the mother, breathing murmur of lungs, movement of gut. At the same time it is not yet able to differentiate the sounds coming from outside the utero, e.g. father’s speech. The child’s skin is covered with little hairs and fetal ointment which protect it against the macerating impact of amniotic fluid. The fetus has already eyebrows and eyelids, but eyes are still covered by embryonic film, thus it cannot still open its eyes. The fetus has no hair or lashes, but nails are already forming on toe and fingertips. The size of the fetal heart already corresponds to the size of one euro coin and the heart beats 120-160 times a minute. This is twice as fast as the mother’s, i.e. the heartbeat of the mother and father together.

During the fetal ultrasound the size and structure of placenta and attachment of umbilical cord to the placenta is assessed. It is essential to assess that the lower edge of placenta would not cover the cervix and would not hinder the birth of the child in the future.

The amount of amniotic fluid is assessed so that there would not be too little or too much of it. By measuring the size of fetal skull, diameter of abdomen and length of the thighbone it is possible to assess the size of the baby and specify the birth date of the child. It is very important to assess the fetal organ structures in detail. Attention is paid that the brain skull were whole and the sutures and fontanels of the skull were open, so that the fetal brain tissue could grow unhindered. The brain structures and their compliance with the size of pregnancy are assessed.

Attention is paid to the baby’s eyes and their distance from each other. The entirety of the upper lip is assessed to ensure the nice smile in the future. The fetal mandible is assessed for having no problems with sucking in the future. Attention is paid to the existence or absence of ultrasound properties characteristic of the chromosomal diseases. Attention is paid to the entirety of fetal backbone and abdominal front wall and umbilical cord proceeding from the abdomen.

The entirety, position and movement of the hands and legs of the fetus are assessed. The fetus bends and stretches its hands and legs and can already close and open its hand. Attention is paid to the existence and structure of kidneys and their function whether the bladder is full and whether bladder is surrounded by the arteries of umbilical cord are assessed. Attention is also paid that the fetus could swallow and the stomach would be full and the latter would be located on the same side with the heart, on the left. Special attention is paid to the fetal heart structures: the heart should have four chambers so that the big blood vessels would proceed from the correct chambers and that the heartbeat of the fetus were regular.

In case of increased risk of prematurity (twin pregnancy, uterus anomalies, prior premature births, prior cervix operations) the length of the cervix can be measured with vaginal sensor and the risk of prematurity can be assessed on the basis of it.

During the foetal anatomical screening of the II. trimester, the risk of preeclampsia obtained during the OSCAR test may be reassessed or preeclampsia screening may be recommended for women whose preeclampsia risk was not assessed during the OSCAR test. 

During the given ultrasound the sex of the child could be also assessed, if required by the family.

At the end of the ultrasound test the results of the ultrasound are explained to the family and in case of deviations the nature, reason and prognosis for the fetus are explained in detail.

It is essential to know that most of the fetuses grow and will be born in good health, by sincerely delighting their parents in the future.

Video: Fetal anatomy scan at 20 weeks. Dr. Marek Šois