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31.1. Technique of fetal blood sampling

98 Genetic Diversity and Disease Susceptibility

contamination with maternal blood is not necessary.

31.2. Complications

32. Fetal skin biopsy

32.1. Technique of fetal skin biopsy

albinism.

Fetal blood can be obtained from the umbilical vein or artery in the umbilical cord near its insertion into placenta. Fetal blood can also be obtained from the intrahepatic umbilical vein or a free loop of umbilical cord. A 22 Gauge spinal needle is used for the procedure. Ultrasound with color Doppler is used to image the site of cord insertion in the placenta. The needle is introduced under ultrasound guidance about 1 cm from the insertion site of the umbilical cord into the placenta. If the cord is punctured close to the placental insertion there are increased chances of contamination with maternal blood. After obtaining the fetal blood sample it is tested for contamination with maternal blood. Kleihauer-Betke test of acid elution with hydrochloric acid can distinguish between fetal and maternal cells. Fetal red blood cells do not get eluted with hydrochloric acid due to presence of fetal hemoglobin. Fetal Red blood

cells have a larger Mean Corpuscular Volume compared to maternal red blood cells.

Intrahepatic portion of the umbilical vein is an alternative site, which yields pure blood samples. Direct fetal cardiac sampling has been resorted to in few centers. When blood is obtained directly from the fetal heart or intrahepatic portion of umbilical vein testing for

When a needle is inserted into the umbilical vein the most common complication is fetal bradycardia. However it should be monitored and it quickly reverts back to normal after the needle is withdrawn. Sometimes a brisk spurt of blood from the puncture site into the amniotic fluid is seen lasting for 2 min. However this bleeding invariably stops and the fetus is unaffected. In cases of continued hemorrhage a bleeding disorder in the fetus should be considered. The overall fetal loss rate following umbilical blood sampling is 1–2%. There is no increased risk of preterm labor, intrauterine growth restriction or fetal congenital malformations.

Fetal skin biopsy is done between 18 and 20 weeks of gestation [35, 36]. This is indicated for the detection of genodermatoses like epidermolysis bullosa, epidermolytic hyperkeratosis, harlequin ichthyosis and Sjogren-Larsson syndrome [37, 38]. Another indication is oculo cutaneous

Fetal skin sampling is done using a special biopsy forceps, which is introduced through a trocar needle. The site of sampling is chosen according to the indication. The site of sampling is different in different indications. In suspected genodermatosis the site of biopsy is gluteal region. When occulo cutaneous albinism is suspected the skin biopsy is taken from the eyebrows and scalp. An electron microscope study of the fetal skin sample is required to confirm

Sudakshina Chakrabarti<sup>1</sup> and Nidhi Sharma<sup>2</sup> \*

\*Address all correspondence to: drbonuramkumar@yahoo.co.in

