Clinical information
Diagnostic Utility:
Determining the fetal sex from the DNA found freely in the plasma of pregnant women (cell-free DNA) allows for an early and non-invasive identification of the fetus's sex.
- In pregnant women carrying a mutation in a gene linked to X chromosome-related diseases, such as haemophilia or Duchenne Muscular Dystrophy, among others, this determination allows for the early identification of male fetuses, and therefore, those potentially at risk of the disease. Only in this case, is it necessary to perform an invasive test to further study and determine if the fetus carries the mutation or not. Female fetuses have two copies of the X chromosome and therefore can only be carriers but will not develop the disease.
- In cases of pregnancies at risk of congenital adrenal hyperplasia in the fetus, the pregnant woman receives treatment with corticosteroids from the knowledge of the pregnancy, aiming to prevent virilization of female fetuses. Early determination of fetal sex allows for discontinuation of the treatment for the pregnant woman in the case of a male fetus.
Method:
Prior to determining fetal sex in maternal plasma, DNA extraction is necessary from a plasma aliquot separated under conditions suitable to minimize the risk of contamination.
The determination is carried out using the real-time PCR technique, using specific TaqMan primers and probes for two specific markers of the Y chromosome, the SRY gene (single-copy marker) and DYS14 (multi-copy marker).
Reference Values
The possible results are: Male Fetus / Female Fetus.
In cases where the result is a female fetus, within a family context of an X chromosome-related disease, the result is reported, and a new sample from the pregnant woman is requested to repeat the determination and confirm the result.
Diagnostic Algorithm: Not Applicable
Turnaround Time: 15 days
Specimen information
Sample: Total blood (sample obtained from week 8 of gestation)
Tube: EDTA K3 10 ml tube
Minimum Volume: 8 ml
Precautions:
- Sample extracted exclusively for this determination
- Untouched vacutainer tube
- It is important that the request specifies if the determination is requested due to the risk of disease transmission linked to the X chromosome.
Stability:
- At room temperature: 3 days
- In refrigeration: 3 days
Transport Instructions: room temperature
Reasons for rejection:
- Sample arrived at the laboratory > 3 days post-extraction.
- Highly hemolyzed sample
- Sample with insufficient volume
Administrative information
BST Code: 4951
Test Description: Determination of fetal sex in maternal plasma
Synonyms: Fetal sex
Section: Immunohematology
BST Rate: Check the updated rates here.
Profiles:
Test 4951 is not included in any profile.
References
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Fernández-Martínez, F., Galindo, A., Garcia-Burguillo A., Vargas-Gallego C., Nogués N., Moreno-García M., Moreno-Izquierdo A. Noninvasive fetal sex determination in maternal plasma: a prospective feasibility study. Genet Med 14, 101-106 (2012) doi:10.1038/gim.2011.8