Fetal Anomalies: Key Information for an Informed Pregnancy

Expecting a child is a time of great illusions and expectations, but it can bring with it a lot of uncertainty. Pregnancy monitoring involves a series of tests to ensure the mother’s well-being and the baby’s proper development. Between 3 and 5% of fetuses have serious fetal anomalies, some of which can be identified as early as the first trimester.

What are fetal anomalies?

Fetal anomalies, also known as congenital defects, are structural, functional or metabolic alterations that occur during fetal development. Some of them are amenable to postnatal treatment, while others are incompatible with life and account for 20-30% of perinatal mortality worldwide.

There are different classifications for congenital defects, depending on their clinical relevance (major or minor CD), the stage of development where they occurred or their clinical presentation. As for their etiology, according to the WHO, in approximately half of all children born with congenital defects it is possible to determine their cause. In 25% of cases the origin is genetic and in 15% the anomalies are caused by environmental factors.

Fetal anomalies due to genetic causes can be divided into 3 main groups:

1.Chromosomal abnormalities: Alterations in the number or structure of chromosomes detectable in the karyotype.

• Numerical: Aneuploidies and Polyploidies. E.g. Down syndrome
• Structural: Deletion, duplication, inversion, Translocation, etc. (E.g. Cri du Chat syndrome)

2. Submicroscopic abnormalities: Alterations involving fragments between 10Kb and 10Mb. They are not generally identified in the karyotype.

• Microdeletions, microduplications and copy number variation (CNVs). E.g. DiGeorge syndrome and 15q13.3 microduplication syndrome.

3. Monogenic diseases: Point variants in genes of Mendelian inheritance.

• Autosomal dominant: Caused by a mutation in a single allele of a gene. E.g. Noonan syndrome, neurofibromatosis, Huntington’s disease, etc.

• Autosomal recessive: Caused by a mutation in each of the 2 alleles of a gene, requiring both parents to be carriers. E.g. Cystic fibrosis, beta-thalassemia, Gaucher disease, etc.

• X-linked: Caused by a mutation located on the X chromosome, usually affecting males. E.g. Fragile X syndrome, Duchenne muscular dystrophy, Hemophilia A and B, etc.

Risk factors and screening tests

There are several factors that may increase the risk that the fetus may have abnormalities, such as advanced maternal age, family history of genetic abnormalities, maternal illness, or exposure to teratogens (substances that can cause birth defects).

The detection of fetal anomalies during pregnancy is performed through different prenatal tests, such as ultrasound scans, screening tests and diagnostic tests. During the first trimester, combined screening is performed to assess the risk of certain genetic conditions and to monitor the health of the fetus and the mother. This monitoring includes the evaluation of the mother’s medical history together with an ultrasound study and the analysis of certain hormones in the maternal blood. It is also possible to additionally screen for aneuploidy in maternal blood, which provides better performance data.

In the second trimester, a detailed morphological ultrasound is performed to detect fetal malformations and analytical studies that will allow detection of gestational diabetes. Finally, within the third trimester, a set of tests including an ultrasound, blood tests and a culture are carried out, with the aim of assessing maternal-fetal well-being, and preparing for the final phase of pregnancy and delivery. If during these examinations, any signs of elevated risk or abnormalities are found, diagnostic tests requiring a sample of amniotic fluid or chorionic villus sampling or chorionic villus biopsy should be performed. In our blog Prenatal diagnosis, what is it and what is it for? We explain more about these diagnostic tests and the different samples they require.

Benefits of advanced prenatal diagnosis

Prenatal diagnosis has undergone great advances thanks to the evolution of genetics. Nowadays, analysis techniques allow a complete evaluation of fetal genetic material. Among the most outstanding advantages are:

• It allows a comprehensive analysis of fetal anomalies, including chromosomal, genetic and point mutations in specific genes.
• The diagnosis allows identification of the cause of possible anomalies detected on ultrasound or screening tests.
• It provides crucial information so that parents, together with their physicians, can make informed decisions about pregnancy management.

In the face of a high-risk pregnancy, it is essential that families and the specialist have genetic information to assist in the screening or diagnosis of possible fetal anomalies, which facilitates informed decision making and the development of an appropriate management plan.

If your pregnancy has been classified as high risk, we recommend that you consult with a genetic specialist. This professional will be able to evaluate your specific case, explain the prenatal screening and diagnostic options available, and help you understand the risks and benefits of each test.

At Veritas we aim to accompany parents from conception to the birth of the baby. This is why we offer different tests for pre and post natal care, such as PregnancyLoss, myPrenatal, PrenatalWES and myNewborn.