When is it done?
The method developed for determining fetal sex has an excellent sensitivity and high specificity, making it suitable for routine use. There are studies which show that it is possible to detect fetal DNA in maternal blood from the 5th week of pregnancy. However, the sensitivity for determination of fetal sex in maternal blood increases between the 5th and the 10th week of pregnancy, with its peak at the 10th week.
From the 8th week of pregnancy, the sensitivity is very high and the test reliability is more than 99% (see table below).
Any pregnant woman can take the fetal sex determination test, preferably
from the 8th week of pregnancy on.
Pregnacy Stage
(Weeks) |
N |
Test Result
|
Female |
Male |
< 8 |
20 |
74,00% |
> 99,00% |
8-12 |
79 |
99,00% |
> 99,00% |
13-17 |
68 |
99,00% |
> 99,00% |
> 17 |
45 |
99,00% |
> 99,00% |
TOTAL |
212 |
|
(Levi et al, 2003) |
N - number of analyses |
As shown in the Table above, when gestational age is less than 8 weeks, the reliability is lower for female results (74%).
Therefore, we recommend that the sample for this test is always collected from the 8th week of pregnancy.