If the fetus is viable, the procedure is performed close to an operating room in case an emergency cesarean section is necessary due to complications caused by the procedure. Currently, there is no definite age of viability because this depends on the fetus’ ability to survive outside the womb, which in cases of premature births, can depend on access to medical care and technology needed to keep the fetus alive through the neonatal stage. Fetal viability typically occurs at about 24 to 25 weeks of gestation. When the fetus is in between the ages of 24–34 weeks, a glucocorticoid is given to the patient about 24 hours before the procedure to stimulate lung maturity. An ultrasound is performed before the procedure to view the position of the fetus and may be used during the procedure to help guide the needle. The mother’s<unk>  is drawn for comparison against fetal<unk> , and intravenous access is established in the mother in order to supply medications as needed. To reduce the risk of intraamniotic infection, antibiotics are supplied through the intravenous access about 30–60 minutes before the procedure. If movement of the fetus is a risk to the success of the procedure, the fetus may be paralyzed using a fetal paralytic drug. This image shows anterior<unk>  sampling from the<unk> <unk> . This image shows posterior<unk>  sampling from the<unk> <unk> . A 20 or 22 gauge spinal needle is typically used in PUBS and may be prepared with an anticoagulant, which helps to reduce the risk of clot formation. During the procedure, the first step is to locate a relatively stable segment of the<unk> <unk> . A typical sampling site would be where the segment of the<unk> <unk>  is closest to the placenta. However, there is a risk of maternal<unk>  contamination at this site.<unk>  sampling may be achieved with more ease if the placenta is in the anterior position. However, if the placenta is in the posterior position, the fetus might block direct access to the<unk> <unk> . Once the<unk> <unk>  is reached and the correct position of the needle is confirmed, the fetal<unk>  is drawn. The needle is removed after all necessary samples are taken. The site of puncture is monitored after the procedure for bleeding. Also, if the fetus is viable, fetal heart rate is monitored post-procedure for one to two hours. After the<unk>  samples are obtained, they are placed into tubes containing anticoagulants in order to stop the<unk>  from clotting. If the<unk>  sample was obtained at the site close to the placenta, a fetal<unk>  confirmation test should be done to ensure no mixing of fetal and maternal<unk>  occurred before the diagnostic tests are done on the<unk> . Fetal red<unk>  cells (RBC) are usually bigger than maternal RBCs, and the average volume of RBCs, the mean corpuscular volume (MCV), is one of the methods used to determine whether or not the fetal<unk>  has been contaminated. Another method, human chorionic gonadotropin (hCG) determination, can detect maternal<unk>  because maternal<unk>  has high levels of hCG. The hemoglobin alkaline denaturation test (Apt test) can detect the presence of maternal<unk> , which is indicated by a color change from red to brown when the sample is added to alkali reagent.<unk>  typing would also detect maternal<unk> , as the I antigen only occurs in adults. The Kleihauer–Betke test can detect very small amounts of maternal<unk>  before the third trimester of pregnancy by monitoring hemoglobin elution in acid because adult and fetal hemoglobin elute differently in acid. Finally, a white<unk>  cell count can detect maternal<unk>  in the sample, as fetal white<unk>  cells are primarily leukocytes, while maternal white<unk>  cells are mostly neutrophils. If amniotic fluid infiltrated the sample, then there would be a reduction in the volume of RBCs, white<unk>  cells, and platelets in the sample. Also, patterns consistent with amniotic fluid would be visible in the sample.
Percutaneous umbilical cord blood sampling
Fetal scalp blood testing
Fetal echocardiography
Amniocentesis
Fetal EEG
Fetal scalp stimulation test
Chorionic villus sampling
Apgar score