What is Amniocentesis?

Amniocentesis consists of the extraction of a small amount of the amniotic fluid via the abdominal route, which envelops and protects the fetus during growth and development.

In the womb, the fetus is housed inside a sac, called the amniotic sac or amnios, filled with a fluid - the amniotic fluid - that protects it from impacts, temperature changes and pressures of various kinds.

Why is it performed?

Amniocentesis is a minimally invasive medical procedure, mainly used for prenatal diagnosis of chromosomal abnormalities, infections and fetal developmental disorders, such as spina bifida and Down syndrome . In fact, the amniotic fluid contains cells, called amniocytes, which come directly from the fetus; once isolated, these cells can be multiplied and used in the laboratory for cytogenetic and / or molecular analyzes.

Index Further information

Technique and risks of amniocentesisWhen will I receive the results? When is amniocentesis performed? What are its indications? What happens if amniocentesis shows anomalies?

Technique and risks

As a rule, amniocentesis is performed starting from the fifteenth week of pregnancy, when the amniotic cavity has reached such dimensions that it does not constitute particular risks for the fetus during the examination. These risks are further reduced by a prior ultrasound scan showing the position of the fetus and the placenta. If the expectant mother is suitable for the exam - which is for example contraindicated in the presence of fever or other infections - the skin of the abdomen is disinfected with an antiseptic solution. Under constant ultrasound guidance, the specialist in obstetrics and gynecology inserts a very thin needle through the skin that covers the underlying uterine cavity, in order to reach the amniotic cavity and take about 15 ml of the homonymous liquid. Consider that at the 14th week of gestation this liquid occupies a volume of about 100 ml, which rises to 150-200 ml 15/30 days later and to 500 ml around the twentieth week. Ultrasound monitoring does not produce ionizing radiation, it is absolutely harmless and as such does not cause any harm to the fetus, on the contrary, it allows to control its position and that of the needle, minimizing the risk of complications.

In the laboratory, a small part of amniotic fluid is used to perform direct biochemical tests, while from the remainder the fetal cells are isolated, subsequently cultivated to obtain a sufficient numerical sample for the evaluation of the karyotype.

The examination is not painful (at the most annoying), lasts a few minutes and does not require special anesthesia or hospitalization; at the end of the amniocentesis it is however necessary to stay for 30-60 minutes in the health center. During the 2/3 days following the examination it is advisable to refrain from heavy physical activities; furthermore, if you experience prolonged abdominal pain or the onset of fever or strange vaginal discharge, it is important to immediately inform your healthcare assistants.

Like all invasive procedures, even if practiced by experienced and well-equipped personnel, amniocentesis has a certain percentage of abortion risk, roughly quantifiable in one out of 200 possibilities. More recent studies, dated 2006, indicate that the additional risk of abortion, compared to women not subjected to amniocentesis, it is particularly low (0.06%) or even zero. It is therefore a safe procedure, characterized by a very small percentage of risks and complications. One of these is canceled by administering to non-immunized Rh negative pregnant women, with Rh positive partner, anti-D immunoglobulin; the injection of these antibodies is necessary for the possible passage of fetal blood into the maternal circulation, with consequent production of immunoglobulins which could damage the baby.

Theoretically, the abortion associated with amniocentesis can be traced back to the development of amniotitis (infection of the amniotic fluid), the rupture of the membranes or the appearance of contractile activity that cannot be controlled with medical therapy. Diagnostic errors and cultural failures that require repetition of the test are extremely rare (<0.2%). Because of these risks it is absolutely necessary that amniocentesis is preceded by the signing of the informed consent by the expectant mother, who has the right to obtain prior all kinds of explanations on methods, diagnostic limits and risks of the procedure.

Considering the costs and above all the rare, but still possible, complications, amniocentesis is not carried out in the case in which the parents exclude a priori any hypothesis of gravidic interruption, unless they want to perform it for the sole purpose of preparing with greater awareness to the birth of a child suffering from some anomaly. Furthermore, it is not a routine examination, but a diagnostic investigation to which only consenting mothers considered at risk are subjected. Beyond this, amniocentesis remains an absolutely optional exam and parents are the only ones responsible for their choice.