Prenatal Care and Genetics

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Prenatal Care and Genetics

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What is prenatal diagnosis?

Usually, at the beginning of a pregnancy, the parents’ enthusiasm makes them unaware of the fact that their child might suffer from various conditions since fecundation. In any pregnancy and at any age there is a risk of physical (3%) and chromosomal (0.5%) malformations. Parents should also bear in mind that apart from this natural risk, there is also an additional one which depends on the mother’s age and on both her own and her direct relatives medical history. Prenatal diagnosis consists of diagnosing physical and chromosomal malformations in the foetus as soon as possible, preferably between the first and the second trimester of the pregnancy. These tests have undoubtedly a reassuring objective for the parents.

FIRST TRIMESTER

TRIPLE SCREENING TEST (multiple-marker screening test)

Biochemical markers can indicate a high risk of chromosomal abnormalities. Thus, this test is not a definitive diagnosis. It is complemented with an ultrasound scan to identify a series of foetal modifications that can be associated with chromosomal abnormalities (neural fold, etc…). If these modifications in the structure of the foetus are observed, a further chromosomal study might be recommendable. The test consists of analysing a blood sample from the mother to measure some biochemical markers (alpha-fetoprotein, human chorionic gonadotropin or HCG …) that assess the risk of foetal malformations because of chromosomal abnormalities. There are also other causes that make the natural risk of having a child with a congenital disorder increase.

CHORIONIC VILLUS BIOPSY (Genetic study – Karyotype)

This test is performed between the 10th and 13th week of pregnancy. It consists of obtaining little fragments of the placenta (chorion) using a pair of biopsy forceps through the uterine neck or alternatively, by transabdominal puncture with a biopsy needle. Its main advantage is that it can be performed at a very early stage (10th-13th week) and it only takes 10 to 12 days to obtain the chromosomal study (karyotype). The risk of complications is low and similar to that of the amniocentesis (0.5-0.8%)..

SECOND TRIMESTER

AMNIOCENTECIS

It is a prenatal diagnosis test to obtain the karyotype of the foetus.

How is it performed?

It consists of practising a little puncture with a thin needle through the mother’s abdomen just above the pubic area, penetrating the uterus and finally reaching the amniotic sac to obtain 14 to 18 cc of amniotic fluid. It is carried out under permanent ultrasound scan monitoring. As amniotic fluid is constantly generated, this quantity is spontaneously replaced in a few days without any risk for the foetus. In this amniotic fluid, cells from the foetus can be found, they are isolated and cultivated in the laboratory for 2 or 3 weeks until their genetic content (karyotype) can be analysed.

What is a karyotype?

The karyotype is the chromosomal map of the foetus that is determined at the moment of fecundation. Chromosomally normal humans have 46 chromosomes. 44 of them correspond to the so called autosomes and the other two are the sex chromosomes which for females are called XX and for males XY.

Is there any risk?

The risk of complications because of an amniocentesis is low, under 0.5%. To perform the test, the amniotic sac must be penetrated by the puncture needle and that means that a little hole will remain. This puncture though will later close spontaneously.

FUNICULOCENTESIS

Funiculocentesis is performed to rule out infections and to carry out foetal genetic tests. It is a prenatal diagnosis technique which consists of obtaining and analysing a blood sample from a vessel of the umbilical cord with the help of a thin needle.It is usually performed after the 18th week of pegnancy and when the sample obtained from a previous amniocentesis does not provide clear results. Exceptionally, it can be performed to transfuse blood to the foetus. It cannot be performed before the 18th week of pregnancy. Its risks are similar to those of amniocentesis. However, the percentage of miscarriage or foetal loss is higher, between 5 and 10%.
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