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Fetal Tissue Biopsy
The concept of using ultrasound guidance for taking a sample of fetal tissue as a means for prenatal diagnosis was initially described in the 1970s. This procedure is used to detect hereditary conditions of the fetus that cannot be identified through more conventional methods such as amniocentesis or chorionic villus sampling of the placenta. For example, fetal skin biopsy is an important diagnostic tool that permits patients who carry an abnormal gene for a severe skin disease to have a pregnancy with the knowledge of whether or not their fetus is similarly affected.
When is it performed?
The biopsy is typically performed between 17-20 weeks gestation. A local anesthetic is used to anestheize the maternal skin. The physician inserts a sheath (trocar) into the mother’s abdomen and through the gestational sac to reach the fetus under continuous ultrasonic guidance. The trocar permits passage of biopsy forceps that is used to obtain a fetal skin sample – typically from the thorax, back, buttocks, or sometimes the scalp. A small amount of intravenous sedation (e.g. diazepam) is used for the mother as needed. Other diseases can also be similarly diagnosed in this manner by sampling fetal liver or muscle. Biopsies of the fetal liver or muscle are performed using a thin needle (typically 16.5 percent gauge) – again, under local anesthesia and light maternal intravenous sedation as needed.
Results and risks
Tissue specimens can be analyzed by using a microscope (e.g. light and electron microscopy) as well as with a variety of other tests such as enzymes. Fetal tissue biopsies are used to detect skin disorders such as bullous disease, pigment cell disorders, and problems with proper development of epidermal appendages (e.g. ectodermal dysplasias). Over time, fetal tissue biopsies will become less common as we improve our understanding of how inherited diseases that are linked to specific genes and how mutations can be characterized by using sophisticated DNA analysis of amniotic fluid, placental tissue, or possibly fetal cells in the maternal circulation.
For example, the prenatal diagnosis of ornithine transcarbamylase deficiency has recently been made easier by the discovery of specific gene mutations. Although this discovery now allows the prenatal diagnosis of this disease by DNA analysis of amniotic fluid or placental tissue, there are still some cases where conventional DNA studies will not be informative for the detected mutation. Fetal liver biopsy could then be used as an alternative diagnostic test.
The main risks associated with fetal tissue biopsies are spontaneous miscarriage, infection, preterm delivery and possible hemorrhage. In experienced centers, the incidence of fetal loss from skin biopsy has been reported to be less than 5 percent.