Prenatal Diagnosis
There are several tests that allow us to discover a great variety of pathology that could affect the fetus and we call them Prenatal diagnosis:
- 11-13 weeks ultrasound scan: The nuchal translucency (ultrasound image of some subcutaneous fluid in the nuchal of the fetus) at 11-13 weeks scan in combination with the maternal age is an accurate screening of Down syndrome.
It gives us, as well, confirmation of pregnancy viability, exact gestational age, early diagnosis of major fetal anomalies and to see the chorionicity, highly important in multiple pregnancies. - EBA Test: It’s a maternal serum screening taken between 11 and 13 weeks of pregnancy. It works with some hormonal results that together with maternal age, weight, gestational age, nuchal translucency and CRL, will give us a risk index for Down Syndrome and Edward Syndrome. The detection rate is about 85-90%.
- Noninvasive prenatal diagnostic test: since early 2013 is available in Spain a new screening test to assess noninvasively alterations in chromosomes 13,18, 21 and sex chromosomes. This test is a maternal blood test to rule out Patau, Edwards, Down and Turner syndromes, respectively, also allows the detection of fetal sex. It has the advantage of greater sensitivity and specificity than the EBA test and it is also a noninvasive test (without any risk of miscarriage).
- Amniocentesis: Performed from 15 weeks of pregnancy onwards. The technique is the introduction of a thin needle, under ultrasound guidance, in the amniotic sac and the extraction of 20cc. of amniotic fluid. It’s the most accurate test to diagnose chromosomal anomalies (close to 100% fiability) but the risk of miscarriage is about 0,5%.
After this test it is essential to do complete rest for about 48hr. The results take 20 days to come back from the lab, but there is a quick result in 24-48hr (FISH for the 13, 18, 21 and X, Y Chromosomes) that you can ask for at the same time.
In the actual guidelines of prenatal diagnosis of the ICS, maternal age is Not a determinant factor to do an amniocentesis, the age of the patient is included in the EBA test.
- Chorionic Villous sampling: It is the subtraction of chorionic villous to do some fetal analysis. It’s done from 11 weeks onwards (between 11 and 14 weeks) and it can be done through the abdomen or the vagina depending on the placental site. It gives us the same information that the amniocentesis but it can be performed earlier.
After it, the patient must rest for 48 hr. The miscarriage rate is about 1-2%. The preliminary results are at 48-72 hr but the definitive ones at 20 days.