The availability of rapid karyotypic diagnosis with both CVS and amniocentesis and their considerably easier utility has resulted in fetal blood sampling (FBS) now rarely being used to assess karyotype. It is now almost exclusively used for the assessment of fetal anaemia or infection. It is performed under sterile conditions with continuous ultrasound guidance. Again a single operator usually performs the ultrasound and needle insertion. A 20-gauge needle is inserted into the placental cord insertion or intra-fetally into the intrahepatic vein, with colour Doppler mapping of the vessels. There are significantly greater risks of FBS than with amniocentesis or CVS. These include fetal bradycardia, haemorrhage, cord haematoma or tamponade and fetal death. Sampling from the intrahepatic cord appears to be safer than the placental cord insertion or free loops of cord. There needs to be immediate access to laboratory facilities for analysis of the fetal blood. Because of the significantly higher density of nucleated cells in an FBS a full karyotype culture of lymphocytes should be available within 48 h.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.