Prenatal diagnosis

Modern methods of prenatal diagnostics 

Prenatal diagnostics is prescribed for:

• Correcting the pregnancy management plan,
• Determining the outcome of the pregnancy,
• Planning for possible complications during labor and delivery of the newborn,
• Deciding whether to continue the pregnancy,
• Identify conditions that may affect the course of the pregnancy

Prenatal diagnosis is performed by various invasive and non-invasive methods. The former involve intervention in the uterus and carry a certain risk for the further course of the pregnancy, so they are used only on strict indications and taking into account all factors. Now more and more non-invasive methods are being developed, which are quite effective and at the same time do not pose a threat to the mother and fetus. 

Invasive 

Invasive methods of prenatal diagnosis include:

• Amniocentesis - amniotic fluid aspiration, usually performed at 15-17 weeks and later in pregnancy. At this stage, the volume of amniotic fluid is about 200 ml. Amniotic fluid contains fetal cells (mostly derived from fetal skin) that can be grown in culture for chromosome analysis, biochemical analysis and molecular biological analysis, determination of fetal cytogenetic abnormalities, which helps in formulating a further plan for the management of pregnancy and labor.
• Chorion biopsy (chorionic villus sampling, CVS) - performed at least 10 weeks gestation. In this procedure, a catheter is inserted through the cervix to the developing placenta under ultrasound control. Cells selected in this way can be analyzed using a variety of methods. The most common of these is chromosomal analysis to determine the fetal karyotype, and biochemical or molecular biological analysis is also performed.
• Transcervical trophoblast cell sampling - detects chromosomal abnormalities, determines the sex of the fetus. It is carried out in the first trimester.
• Embryoscopy and fetoscopy - a probe is inserted into the uterus to observe and/or sample fetal blood and tissue. Performed in the second or third trimester.

Non-invasive 

Non-invasive methods of prenatal diagnosis include:

• Ultrasound echography is a routine procedure and is safe for the mother and fetus. The developing embryo can be seen for the first time at about 6 weeks of pregnancy. Screening for possible abnormalities is best done starting at 16-20 weeks.Ultrasound gives good visualization, helps to determine the anatomy, size and position of the fetus, assess the condition of the placenta, the amount of amniotic fluid, but often these data are not enough. Minor abnormalities may be detected only later in pregnancy. Such an example is Down syndrome (trisomy 21 chromosome), in which anomalies are often not pronounced, and can be identified only by indirect signs, such as thickening of the collar space.
• Maternal blood testing for fetal DNA - this method utilizes the phenomenon of fetal blood cells entering the maternal circulation through the villi of the placenta. The modern FISH method is used to identify specific chromosomes of fetal cells extracted from maternal blood to diagnose conditions such as trisomy or X monosomy. 
• Maternal serum alpha-fetoprotein. The developing fetus has two major blood proteins, albumin and alpha-fetoprotein (AFP). Normally, only a small amount of AFP enters the maternal blood, but when there is a fetal disruption, such as a neural tube defect, much more AFP is released into the amniotic fluid, making it possible to diagnose this severe malformation. The highest sensitivity of the method is recorded at 16-18 weeks.
• Maternal serum beta-hCG - most often used for the diagnosis of pregnancy, as well as in suspected abortion or ectopic pregnancy, since its indicators in this case will be much lower than expected. In the middle and end of the second trimester, the test can be used to detect chromosomal abnormalities such as Down syndrome.
• Maternal serum estriol - helps assess fetal viability, placental functionality and maternal well-being. Its measurement in the third trimester gives an indication of the general condition of the fetus and the presence of some developmental abnormalities.

Stages of prenatal screening 

Screening tests are done to determine how likely a baby is to have certain birth defects, many of which are genetic disorders. They include blood tests, ultrasounds, and DNA screening and do not provide a definitive diagnosis. If the results indicate an increased risk of a condition, your doctor may order diagnostic tests.
Depending on the trimester, screening tests may include different tests.

1st trimester 

• Blood tests, including tests for TORCH infections
• Ultrasound with measurement of the posterior cervical space as a marker for possible Down syndrome

2 trimester 

• Blood tests for risk of chromosomal abnormalities.
• Fetal ultrasound to evaluate possible heart, neural tube and other organ malformations

3 trimester

• Fetal ultrasound to evaluate fetal development, placenta and blood flow.

Prenatal diagnostic tests are used to confirm or refute a diagnosis and are performed when indicated.
Prenatal testing may be offered in these cases:

• Age of the mother at which the likelihood of having a child with a chromosomal abnormality increases
• Family history or previous child with a genetic condition
• Parents are known carriers of a specific genetic disease.
• Abnormal ultrasound findings
• Screening test results

The results of prenatal diagnosis enable decisions to be made about the management of pregnancy and childbirth, and to prepare the necessary measures to treat the child immediately after birth, if necessary.