Antenatal diagnosis is the number of available methods and techniques to control the development of the foetus before birth. Every pregnant woman must undergo an individual study, making sure the correct method or technique is applied.
To comprehend these diagnosis methods, we have divided them into two groups:
Non invasive techniques
- Clinic. After writing the patients clinical history, a number of situations may arise in which invasive tests may need to be carried out: advanced age, records of abnormal pregnancies or brain damage, parents with chromosome anomalies, family records of malformations, etc.
- Fetus DNA test in the mother's blood. The test can be performed from week 10, with the ability to know in two weeks the risk of suffering Trisomy of the 21 chromosome (Down Syndrome), Trisomy of the 18 chromosome (Edwards Syndrome) and Trisomy of the 13 chromosome (Patau Syndrome). With a simple blood sample from the mother, some fetal DNA is obtained and can be identify and quantify through an advanced technological process:massively parallel sequence. Finally, a statistical analysis of suffering any of the anomalies mentioned is obtained. The sensibility or reliability of the test is very high, as it has screening rates higher than 99% with false positives lower than 0,1%. Is not useful in multiple pregnancies but it can be applied in all other pregnancies achieved after assisted reproduction treatments, included the egg donation ones.
- Blood test. Between weeks 9 and 12 pregnancy proteins can be accounted for. Beta-HGC and PAPP-A (plasmatic protein A), are proteins that must be kept controlled given that any increase or lack of them may be related to chromosome illnesses.
- Ultrasound. This method is a very important one for the exploration of antenatal diagnosis and has to be done at specific times during pregnancy:
- First trimester. It allows us to capture images considered “chromosomal abnormality markers”. The most reliable and accepted one is known as “nuchal translucency”, this structure can be visualized at the skin fold behind the nape of the neck between weeks 11 and 14. If it exceeds certain dimensions, (3mm), we will offer you an invasive test. Equally important is to measure the nasal bone since lacking it could be related to Down’s syndrome.
- Second trimester. Especially around week 20, time when most anatomic abnormalities can be detected. This must be performed by highly trained professionals. Equipment is also a very important factor as it allows us to detect, through the latest technology: colour Doppler ultrasound and 3-D & 4-D ultrasound, very precise details of foetal anatomy.
- Combined studies. This is called the combined test of the first trimester or EBA-Screening (ultrasound and aneuploide biochemical screening). It consists of a computerized study that calculates the level of risk of any chromosomal abnormality (especially Down’s syndrome), using the age of the pregnant woman, blood test markers (mentioned above) and the measurement of the nuchal translucency. The results show a rate of detection very close to 90%, with an acceptable rate of false positive results of a 3%.
- Pre-implantation Genetic Diagnose (P.G.D.).
- Chorionic villus sampling. Its main objective is to remove a small sample of tissue (Chorionic villi) from the uterus during early pregnancy to screen the baby for genetic defects. This is obtained via the abdomen or via transcervical. DNA and foetal enzymes are also studied. It presents a clear advantage over amniocentesis: it can be done much earlier, in weeks 11 and 12, and the rate of complications is similar.
- Amniocentesis. It’s the extraction of amniotic liquid that surrounds the foetus, through the mother’s abdomen. It’s usually don between weeks 15 and 18 Molecular Biology’s latest developments make possible the detection of specific chromosomal alterations within the amniotic liquid. This technique is known as Fluorescent In Situ Hybridization (FISH) and it allows us in a term of 24-28 hours, and with same technique to obtain amniotic liquid, and the same quantity, to analyze the chromosomes involved in the most frequent numerical alterations in newborns.
- Cordocentesis. Also known as Percutaneous Umbilical Cord Blood Sampling (PUBS), it’s the extraction of foetal blood. Guided by the ultrasound the doctor uses a thin needle which is inserted into the umbilical cord to retrieve a small sample of blood. The test is done between weeks 19-20 it examines blood and searches for chromosomal abnormalities and blood disorders.
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