Antenatal diagnosis

Content

Introduction

By prenatal diagnosis we mean a set of investigations, both instrumental and laboratory, which aim to monitor some aspects of the state of health of the fetus during pregnancy, from the early stages of embryonic development to the moments before childbirth (Video) .

In the general population, the probability of having a child with a problem present at birth (congenital) is approximately 3%; in 1% of cases they are anomalies affecting chromosomes or DNA, in the other cases of congenital malformations (for example of the heart or kidneys) or other diseases (for example, infectious diseases or enzymopathies).

All the prenatal investigations available (ultrasound scans, non-invasive tests and invasive tests) allow to identify only some diseases or pathological conditions and it is important that each couple choose with awareness whether to undergo them or not. Offering the couple an interview with a geneticist that allows them to make an informed and conscious choice is an integral part of prenatal diagnosis (read the Hoax).The assessment of the possible risk of disease by a geneticist confirms whether there is only a generic risk, equal to that of the entire population, or whether specific risk factors (for example, parents with healthy carriers of a genetic anomaly) or related risk factors are present. old maternal age (eg, Down syndrome risk) or previous prenatal screening results (eg Down syndrome risk from a combined test).

Prenatal investigations allow the early detection of diseases that can be caused by DNA abnormalities, by chromosome alterations, by infectious diseases contracted during pregnancy, such as rubella or toxoplasmosis, by taking drugs that can induce fetal malformations and other causes some of which can be cured in utero before birth Sometimes, it is also possible to identify some congenital defects, for example of the kidneys and urinary tract, which can be surgically treated immediately after the birth of the baby to avoid irreversible damage.

The main objectives of prenatal diagnosis are to provide information to all couples and, in the event of a high risk of congenital diseases, to inform them of the existence of a targeted test for ascertaining (diagnosing) the presence of specific anomalies. moreover, to identify some diseases affecting the fetus and, when possible, to establish pharmacological or surgical treatment before birth. childbirth assistance, and to arrange for an adequate medical and psychological care of the parents.

The tests

Prenatal diagnostic techniques can be invasive or non-invasive.

Non-invasive tests are 100% safe for the fetus as well as for the woman, but only provide an estimate of the risk of the presence of certain chromosomal abnormalities, particularly trisomy 21 (Down syndrome), 13 or 18 and, possibly, sex chromosome abnormalities. For this they are considered test of screening, i.e. tests that identify a possible risk of disease, the likelihood that it may be present.

Invasive tests, on the other hand, allow to ascertain the presence of anomalies related to DNA and chromosomes and for this reason they are called diagnostic tests. However, they carry a risk of miscarriage.

Non-invasive tests

  • ultrasound, a technique that allows you to check and follow the development of the embryo and fetus. It is used to guide the samples taken during invasive prenatal investigations. It is the most used technique because it is based on ultrasound which, to date, have not shown any harmful effects on the fetus. The "Physiological pregnancy" guideline of the National Guidelines System of the Istituto Superiore di Sanità recommends the execution of two ultrasound scans in pregnancy: the first, within the 14th week to verify the implantation of the embryo inside the uterus and to define the time of conception by correcting any errors deriving from the calculation based only on the date of the last menstruation; the second (called "morphological"), between the 19th and 21st week of pregnancy to evaluate the anatomy of the fetus and exclude malformations identifiable by this test. Both are offered free of charge by the National Health Service. If the attending physician requests it, during pregnancy it is also possible to perform other ultrasound scans, the most frequent being the one performed in the third trimester to evaluate fetal growth, of the placenta and the amount of amniotic fluid
  • fetal echocardiography, ultrasound examination performed in order to examine the heart of the fetus to rule out the presence of a pathology or a congenital malformation. It is carried out during the second trimester (starting from the 20th week) following a reasoned request from the doctor
  • biochemical analysis of maternal blood (combined test, tri test, integrated test), which identify a possible risk of disease. The combined test also provides for the execution of an ultrasound to evaluate the thickness of the so-called retro-nuchal fold of the fetus which, together with the results of the blood test, allows to estimate the risk of certain chromosomal abnormalities. The National Health Service offers free to all pregnant women, regardless of maternal age, these screening tests to assess whether or not to undergo invasive tests, after a documented individual risk assessment. fetal "present in the maternal blood already from the 10th week of pregnancy is also performed on a blood sample taken from the pregnant woman but, unlike the other non-invasive tests, it has not yet been included in the Essential Levels of Assistance (LEA) provided by the National Health Service because not all of the national territory has public laboratories capable of guaranteeing its provision, it is therefore an exam offered privately

Invasive diagnostic tests

  • villocentesis o Chorionic villus sampling, is performed in the first trimester of pregnancy (after the 10th week) by introducing, under ultrasound control, a needle through the maternal abdomen to collect chorionic villus cells and examine them for any DNA abnormalities. More rarely, the removal of small portions of tissue is performed through the vagina and the cervical canal. The risk of abortion related to the method is between 1-2%
  • amniocentesis, is carried out in the fourth month of pregnancy (between the 15th and 18th week) by introducing a needle, through the maternal abdomen, to withdraw about 20 cc of amniotic fluid containing fetal cells. The so-called investigation of the karyotype (chromosome map) to look for any chromosomal abnormalities. The risk of abortion related to the procedure is around 0.5-1.0%
  • cordocentesis, performed after the 16th week, consists of taking the blood of the fetus through the blood vessels of the umbilical cord. The risk of abortion related to the examination is about 2%, higher than that of CVS and amniocentesis. For this reason, cordocentesis is performed only in particular situations (for example in the case in which the woman has contracted some serious infectious diseases during the pregnancy)

In-depth link

National Guidelines System (SNLG). Physiological pregnancy

National Guidelines System (SNLG). Pregnancy agenda

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