Prenatal diagnosis: fetoscopy, triple blood test

Parents who have an increased risk of having offspring with congenital deformities are offered prenatal diagnostics, according to the results of which an acceptable treatment plan can be developed to minimize the consequences of the fetal defect or to give the future parents the opportunity to terminate a pregnancy that will end in the birth of a child with significant deformities.

The high-risk group includes women over 35 years of age (chromosomal defects); those who have already given birth to children with deformities or have a family history of hereditary diseases; representatives of a high-risk population (sickle cell anemia in Caribbean people of African descent).

Problems of prenatal diagnostics

• Stress and anxiety when receiving false positive screening test results.
• Unjustified termination of a normal pregnancy, for example, a situation where a male fetus is aborted while the hereditary disease is linked to the X chromosome.
• Most congenital anomalies seen in low-risk groups are not detected by random screening.
• Availability of medical services varies across regions.

Determination of alpha-fetoprotein

Maternal serum is tested for alpha-fetoprotein at 17 weeks of pregnancy. Its level is elevated if the fetus has an open (but not closed) neural tube defect or umbilical hernia, or when, in twin pregnancies, defects such as posterior urethral valves and Turner syndrome are present. Alpha-fetoprotein levels are low in pregnancies with Down syndrome and in mothers with diabetes. Because the test is non-specific, it is used for preliminary screening: those who test positive may be offered further testing.

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Triple Blood Test

Determination of maternal serum levels of alpha-fetoprotein, unconjugated estradiol, and human chorionic gonadotropin is performed in relation to maternal age, body weight, and gestational age. This allows the risk of neural tube defects and Down syndrome to be assessed. If this test and subsequent screening of mothers at risk were available to all mothers, early recognition of Down syndrome would increase from 15 to 50% (Scheurmier hypothesis), as shown in a large prospective study (N = 12,603).

Amniocentesis

Amniocentesis is performed under ultrasound control at about 18 weeks of pregnancy. The frequency of fetal loss after such manipulation is about 0.5%. The content of alpha-fetoprotein is determined in the amniotic fluid (this is a more accurate study for detecting neural tube defects than determining alpha-fetoprotein in the mother's blood serum), and the cells of the amniotic fluid are cultured to study the karyotype, determine the activity of enzymes for gene analysis. The study of the cell culture takes 3 weeks, so an abnormal pregnancy can be terminated somewhat later.

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Chorionic villus sampling

At 8-10 weeks, samples of the developing placenta are collected for testing using a transcervical catheter or transabdominal needle under ultrasound guidance. Karyotyping takes 2 days, enzyme activity and gene analysis take 3 weeks, so the opportunity to terminate an abnormal pregnancy is provided earlier, with greater safety and less stress than after amniocentesis. The incidence of fetal loss after chorionic villus sampling is about 3% (0.8% higher than after amniocentesis). This procedure does not detect neural tube defects in the fetus,

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High Resolution Ultrasound

From 18 weeks onwards, an experienced specialist can identify an increasing number of external and internal structural anomalies.

Fetoscopy

It is performed starting from the 18th week under ultrasound control. External fetal malformations can be detected, fetal blood samples and organ biopsies are taken. The frequency of fetal loss is about 4%.

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