During pregnancy, it can be definitively diagnosed whether the child has a genetic disease. In this regard, the expectant mothers are evaluated from the first examination and a specific risk assessment is made for each of them. It is important to determine the risks of all expectant mothers by assessing their current condition and performing detailed ultrasound screening from the first trimester onwards, and applying screening or definitive diagnostic methods for specific risk groups depending on their condition.

Expectant mothers who belong to a higher risk group:

• High maternal age: Expectant mothers older than 35 years of age.
• Expectant mothers with a history of repeated pregnancy loss
• Couples with a history of anomalies at birth
• Couples with a family history of genetic or metabolic disease
• Couples with a family history of hereditary diseases

GENERAL APPROACH IN PREGNANCIES

1. Assessment of the Expectant Mother and Father:

If the expectant mother and father or their families have been diagnosed with genetic diseases, the family pedigree and genetic history will be collected. Accordingly, a risk analysis for possible genetic disease in the child will be performed.

2. Screening tests
   1. Dual/combined screening test (11-14 weeks), triple or quadruple screening test (15-20 weeks): They allow screening for trisomies and neural tube defects depending on the week of gestation. The components are age, blood tests, and an ultrasound examination. These tests do not provide a definitive diagnosis; the result allows a risk analysis and is not definitive.
   2. Cell-Free Fetal DNA Test in Mother’s Blood:
      It is performed with blood taken from the mother after the 10th week of pregnancy. It is a very informative screening test that detects free DNA particles of the baby circulating in the mother's blood. It is a method that has different names depending on the company, such as free fetal DNA in maternal blood, cfDNA (Cell Free DNA), non-invasive prenatal test (NIPT test). The cfDNA test can detect Down syndrome (trisomy 21) in over 99%, trisomy 18 in 96% and trisomy 13 in 92% of cases. It can also be used after treatments such as IVF, ICSI or egg donation and in twin pregnancies. Sometimes results are not obtained due to an insufficient amount of free fetal DNA or other reasons. If a chromosomal abnormality is detected, it must be confirmed by amniocentesis or CVS. Thus, it is not a substitute for amniocentesis. However, it significantly reduces the number of pregnancies in which amniocentesis is required.

3. Ultrasound Examination:
   Ultrasonography is our primary tool for evaluating structural and some functional abnormalities. This is also categorized by weeks of gestation:
   1. Early detailed ultrasound examination and genetic screening consultation at 11-14 weeks of gestation,
   2. Detailed fetal ultrasound examination between 20-23 weeks of gestation;
   3. Sometimes fetal examination at 28 to 32 weeks of gestation is required to assess appropriate fetal development.
      • Success of ultrasound and screening tests in detecting Down syndrome:
   4. Despite the above screening tests and ultrasounds to identify pregnancies at high risk for genetic abnormalities, not all fetuses with Down syndrome can be diagnosed during pregnancy. Fetuses/babies with Down syndrome can be detected:
      • About 90% of them with the dual/combined test;
      • About 80-82 % with the quadruple screening test;
      • About 65-70% with the triple screening test;
      • About 80% of them with detailed fetal ultrasound screening.

4. Prenatal Diagnosis
   Prenatal diagnosis is the use of definitive diagnostic tests during pregnancy when the fetus is at high risk for possible structural and genetic disorders.

• • Which expectant mothers should undergo definitive prenatal diagnostic testing?
    • Expectant mothers who are determined to be at risk by double (combined), triple, and quadruple screening tests;
    • Expectant mothers whose cfDNA test results suggest an abnormality;
    • Expectant mothers with structural anomaly(s) detected on detailed fetal ultrasound examination;
    • Expectant mothers with marker(s) that increase the risk of chromosomal anomaly detected on detailed fetal ultrasound examination.
    • Expectant mothers who have had a child born with chromosomal anomaly in a previous pregnancy;
    • The expectant mother or father is a carrier of chromosomal anomaly;
    • The expectant mother's fears and desire for a definitive diagnosis for various reasons.

 

• Some examples of structural pathologies that require prenatal diagnosis after detailed ultrasound examination:
  • Severe growth retardation
  • Amniotic fluid disorders (oligohydramnios – too low; polyhydramnios – too much)
  • Fluid accumulations in different parts of the fetal body: cystic hygroma, nonimmune hydrops fetalis (NHHF), pleural effusion,
  • Alterations of the fetal nervous system and neck: Hydrocephalus, ventriculomegaly, nuchal edema
  • Cardiac anomalies
  • Alterations of Fetal digestive system and abdominal wall: Duodenal atresia, omphalocele
  • Alterations of urinary tract: Obstructive uropathy.
• Which diagnostic tests are performed according to the gestational week?
  • Chorionic Villus Sampling (CVS): In CVS, a small sample is taken from the fetal placenta and the fetal tissue is examined by genetic analysis. Genetic diseases can be diagnosed from the 11th week of pregnancy.
  • Amniocentesis: A sample (usually 15-20 cc) is taken from the amniotic fluid containing the baby. Generally, this procedure is performed between 16 and 23 weeks.
  • Cordocentesis: Cordocentesis is performed in the later weeks of pregnancy by taking some blood (usually 2-3 cc) from the baby's umbilical cord. This test, which is performed after the 20th to 22nd week of pregnancy, is used to diagnose various diseases.

For a more detailed list of genetic diseases, please click on the link below:

https://en.wikipedia.org/wiki/List_of_genetic_disorders