Today, numerous tests are available to expectant mothers to check on the health of their unborn child.
In the first trimester, ultrasound can provide information on the correct implantation of the pregnancy, the viability of the fetus and, in some cases, on multiple pregnancy.
It should be noted, however, that the earliest diagnosis of pregnancy is obtained through a urine test to detect the placental hormone beta-hCG, which can already be detected just a few hours after a missed period.
For a proper ultrasound visualization, two to three weeks of delay are needed, bearing in mind that while the date of the last menstrual period is known, the date of ovulation and consequent conception is not known with precision. In fact, the estimated due date calculated on the basis of the menstrual cycle frequently does not match the more precise one provided by transvaginal ultrasound.
It is called the estimated date because it marks the completion of 40 weeks; a physiological birth can begin anywhere between 38 and 42 weeks.
Once the pregnancy has been confirmed to be developing normally, it is already time to think about prenatal diagnosis of chromosomal conditions.
The trisomies: trisomy 21, or Down syndrome, trisomy 13, trisomy 18, and alterations in the number of sex chromosomes.
CHORIONIC VILLUS SAMPLING AND AMNIOCENTESIS ARE INVASIVE TESTS. To obtain fetal cells from the chorionic villi or from the amniotic fluid, it is necessary to enter the «fetal space», which carries a risk, albeit a small one, of complications.
The diagnosis, however, is reliable, because it allows the chromosomes of the future baby to be mapped.
NON-INVASIVE tests carry no risks but provide probabilistic results, even if with a high degree of reliability. If they indicate a probability of a condition, they must be confirmed with chorionic villus sampling or amniocentesis.
NUCHAL TRANSLUCENCY is an ultrasound examination that can be performed around the 12th week to measure the space beneath the skin at the back of the baby's neck, which is increased in cases of Down syndrome and other fetal conditions. Visualization of the nasal bone increases the reliability of the diagnosis. Normal results for these two measurements allow around 80% of affected fetuses to be identified.
Combining the ultrasound with a maternal blood test measuring two substances produced by the placenta, beta-hCG and PAPP-A, raises the diagnostic accuracy to 90%. This combined test is known as the COMBINED TEST, DUO TEST, or DUO SCREEN.
A study of fetal DNA, obtained through a maternal blood sample, is also available today.
The detection rate for Down syndrome using this test rises to around 99%, and it is also highly reliable for the other trisomies, 13 and 18. It also makes it possible to determine the fetal sex and detect abnormalities in the number of fetal chromosomes. Information can also be obtained about microdeletions, meaning the absence of small portions of a chromosome; in this case, however, reliability is lower and the cost is higher.
Choosing which test to undergo is not always easy. It should be noted that these tests are recommended but not mandatory, and only cover the conditions mentioned above.
You should not settle for a few pieces of information given hastily, nor rely solely on the internet on your own.
It is a good idea to discuss the matter with professionals (a gynecologist, a geneticist), asking all the questions and raising all the doubts that come to mind, in order to make the best decision and clearly understand both the opportunities offered and the limitations of the tests to be performed.
The MORPHOLOGY SCAN at 20 weeks will then provide further information on the health of the fetus.