What Causes Birth Defects to Develop in the First Trimester?


A birth defect is an abnormality in the way that an organ or a body part develops. Birth defects form as the result of genetic and/or environmental factors that affect the health of a developing baby during pregnancy.

The majority of birth defects occur during the first trimester of pregnancy. The first trimester is the most crucial time for developing fetuses, and is when they are most vulnerable to birth defects. This is because, during the initial 12 weeks of gestation, every major organ system of the fetus forms.

How Do I know Whether My Child Has a Birth Defect?

Certain birth defects can be seen and diagnosed during pregnancy. In addition, some physical abnormalities, like structural heart defects or neural tube defects, are associated with certain genetic and chromosomal disorders.

If an individual knows that they have a family history of an inherited genetic condition, or if they have a higher than average risk of having a child with a chromosomal disorder, like Down syndrome, a doctor may recommend prenatal testing.

Noninvasive prenatal genetic testing is the first test in a series of prenatal testing options that provide parents more information about their pregnancy. Noninvasive prenatal testing uses a blood sample from the mother to obtain results. This test can be performed as early as 10 weeks in pregnancy, which is one reason why it is a desirable test for women and couples expecting a child. Results obtained from a noninvasive prenatal test can indicate to a doctor the risk that a child may have a chromosomal disorder, like Down syndrome, and will help them determine additional relevant testing options.

How Do Birth Defects Occur?

There are numerous reasons why birth defects occur. However, it may not always be clear why a child develops a birth defect. Below is a guideline that outlines possible reasons why birth defects can occur in the first trimester.

Genetic Mutations and Chromosomal Abnormalities

Genetic mutations and chromosomal abnormalities are the primary cause of genetic disorders. Some conditions, like Huntington’s disease or cystic fibrosis, occur when the child inherits a gene that is associated with a specific genetic disorder from one parent (dominant disorder) or both parents (recessive disorder). Some disorders, like Down syndrome, occur randomly.

Illness in the Mother

Illnesses, like the flu, are associated with high fever. Fever in the mother during pregnancy has been linked to birth defects, like neural tube defects, that affect the brain and the spinal cord. If a mother has a fever while pregnant their body temperature will increase and can lead to hyperthermia (elevated body temperature) for the baby. The majority of the time, pregnant women who become ill and have a fever will give birth to a healthy child. However, it’s important to manage the fever properly.

Chronic Health Conditions in the Mother

Chronic health conditions in a pregnant woman increase the risk of birth defects. Scientists have discovered that high blood pressure increases the risk of structural heart defects and neural tube defects in developing babies. Smoking and alcohol use during pregnancy significantly increase the risk of developing high blood pressure. If you smoke or drink alcohol regularly, consider quitting months before planning a pregnancy.

Prenatal Care With an Obstetrician

If you’re planning a pregnancy, or if you have recently found out that you’re pregnant, make an appointment to see an obstetrician. Consistent prenatal care allows your doctor to monitor your health and the health of your baby.


Why Do Most Birth Defects Develop During The First Trimester?