Some foetal abnormalities can be improved or resolved with foetal treatments within the mother's womb. At other times, the possibility of not continuing the pregnancy is assessed together with the parents if the foetal or maternal prognosis is harmful.

What are congenital defects?

We understand congenital defects as being those anomalies that occur during embryonic or foetal development. They can affect structural, operational or both elements, and can be mild or serious. It is estimated that they occur in 3-6% of pregnancies.

Who are prenatal diagnoses intended for?

An assessment at the beginning of pregnancy is offered to all pregnant women to identify those risk factors that may predispose the baby to developing a congenital anomaly. One of the objectives of prenatal diagnosis is to be able to identify any alteration as early as possible.

Some women have an increased risk of developing a congenital anomaly from the beginning of pregnancy:

1. Children with chromosomal alterations or other congenital anomalies.
2. One of the two parents is a carrier of genetic alterations.
3. One of the two parents is a carrier of an anatomical anomaly, such as congenital heart disease.
4. A woman with endocrine disorders that may predispose the foetus to abnormalities.
5. Exposure during pregnancy or prior to it to contraindicated drugs, radiation or toxic substances.
6. Exposure during pregnancy or a relevant infection prior to it.

What is prenatal screening?

The purpose of prenatal screening is to identify those pregnant women with a higher risk of presenting a congenital anomaly.

The main prenatal screening tests are:

• Combined first-trimester biochemical-ultrasound screening: currently, it is the first-choice screening method. It consists of the estimation of the probability that the foetus is affected by Down syndrome, Edwards or Patau (T21, T18 and T13) from the risk inherent to maternal age modified by the biochemical markers of blood analysis (bHCG and PAPP -α) and ultrasound (nuchal translucency) of the first trimester. It offers a 90% detection rate for Down syndrome. It can be done from 11 + 0 weeks to week 13 + 6.
• Combined second-trimester biochemical-ultrasound screening: consists of estimating the probability that the foetus is affected by Down syndrome, Edwards or Patau (T21, T18 and T13) from the risk inherent in maternal age modified by second-trimester biochemical markers. It offers a 75% detection rate for Down syndrome. It can be done from week 14 + 0.
• Second trimester morphological ultrasound: performed between week 19 and 22. Its purpose is to assess foetal anatomy and growth, placenta, umbilical cord and amniotic fluid.
• Third-trimester ultrasound: foetal position and growth, placenta and amniotic fluid are assessed. The foetal anatomy is again evaluated to rule out late-onset abnormalities or developmental anomalies.
• Non-invasive foetal blood test: consists of estimating the probability that the foetus is affected by Down syndrome, Edwards or Patau (T21, T18 and T13) based on the detection of the foetal DNA-free fraction in maternal blood. Offers a 99% detection rate for Down syndrome.

What are prenatal diagnostic techniques?

Once we have detected a higher risk of congenital defect in a pregnant woman, a prenatal diagnostic test must be offered to confirm the anomaly.

• Chorion biopsy: analysis of a sample of placental material obtained via an abdominal or vaginal puncture. It can be done between 11 + 0 and 13 + 6 weeks.
• Amniocentesis: analysis of the amniotic fluid obtained via an abdominal puncture. It is done from week 15 + 0.

Correct advice from professionals is important for deciding on which genetic study is most appropriate to apply in each case, considering each of their scopes and limitations (rapid study or QF-PCR/FISH, karyotype, Array-CGH, test microbiological or molecular specific).