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Maternal and fetal blood cells may mix during an amniocentesis and, as a result, patients with rhesus (RhD) negative blood types carrying a RhD positive fetus are at risk of Rh sensitization. [42] [1] Rh sensitization is a process in which maternal antibodies form against red blood cell RhD antigens. [20]
This can be done earlier than amniocentesis, but may have a higher risk of miscarriage, estimated at 1%. After 10 weeks More invasive Amniocentesis: This can be done once enough amniotic fluid has developed to sample. Cells from the fetus will be floating in this fluid, and can be separated and tested.
Secretion of hCG can occur as soon as 6 days following ovulation and on average 8–10 days following ovulation; this is the earliest hCG can be detected in a blood sample. [7] [5] [8] The hCG concentration in blood is higher than in urine. Therefore, a blood test can be positive while the urine test is still negative. [9] [10]
Finally, a white blood cell count can detect maternal blood in the sample, as fetal white blood cells are primarily leukocytes, while maternal white blood cells are mostly neutrophils. If amniotic fluid infiltrated the sample, then there would be a reduction in the volume of RBCs, white blood cells, and platelets in the sample. [9]
Isoimmunization occurs when the maternal immune system is sensitized to red blood cell surface antigens. The most common causes of isoimmunization are blood transfusion, and fetal-maternal hemorrhage. [13] The hemolytic process can result in anemia, hyperbilirubinemia, neonatal thrombocytopenia, and neonatal neutropenia. [7]
The common autosomal trisomies (21, 18, 13) made up a smaller number of cases of mosaicism detected on CVS, but were more often confirmed in fetal tissue (19%). [3] On the other hand, the uncommon autosomal trisomies accounted for a greater number of placental mosaicism cases, but were less often confirmed in fetal tissue (3.2%). [3]
A Rhc negative mother can become sensitised by red blood cell (RBC) Rhc antigens by her first pregnancy with a Rhc positive fetus. The mother can make IgG anti-Rhc antibodies, which are able to pass through the placenta and enter the fetal circulation. If the fetus is Rhc positive alloimmune hemolysis can occur leading to HDN.
However, publications have shown that in comparison with flow cytometry methods, the KB Test overestimates FMH due to false positive results when F-cells are present in the maternal blood sample. Background counting errors can result in estimates of as much as 5 mL fetal blood loss when there actually is no such blood loss, but standard methods ...