According to the Centers for Disease Control (CDC), one in 33 babies is born with a congenital disability. Any agent that can cause an abnormality in an embryo or fetus is called a teratogen. These agents can lead to physical malformations, neurological problems, or even miscarriage or stillbirth. Various factors influence how teratogens can affect a pregnancy, including the genetic susceptibility of the mother and fetus, the route and dose of exposure, and the stage of pregnancy at exposure.

Classes of Teratogens

There are four classes of teratogens. Maternal illnesses such as diabetes can affect the development of the fetus, as can physical teratogens such as heat exposure or radiation. Chemicals such as certain medications, drugs, and toxins, can be teratogenic as well. The final class of teratogens is infections during pregnancy, which can include sexually transmitted infections, chickenpox, shingles, and other viral, bacterial or fungal infections.

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The teratogenic effects of alcohol during pregnancy depend on how much alcohol the pregnant woman ingests over a period of time. Fetal alcohol syndrome (FAS) describes a range of challenges newborns inherit due to maternal alcohol consumption. Babies with FAS have facial abnormalities as well as microcephaly, where the skull is abnormally small and leads to poor brain development. Additionally, many have learning and behavioral problems due to changes in the various parts of the brain.

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Excessive Heat

In a study of almost 24,000 pregnant women, doctors found that hyperthermia — a body temperature of 101 degrees Fahrenheit or higher — was a teratogenic risk. Abnormally high temperatures disrupt protein synthesis in the embryo, causing premature cell death and interrupting the blood supply from the placenta. Because of this, babies can be born with malformations of the heart, brain, spine, and spinal cord. While fevers are unavoidable, pregnant women are cautioned against spending more than 10 minutes at a time in hot tubs and saunas.

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ACE inhibitors

Many people use a class of medication called angiotensin-converting-enzyme of ACE inhibitors to control blood pressure. Taking ACE inhibitors, particularly after the first trimester, is known to cause significant harm to the fetus. These drugs reduce the amniotic fluid surrounding the baby. As a result, problems in the lungs, kidneys, or skull can develop, and in some cases, can lead to stillbirth. While some experts believe these medications are safe during the first trimester, there is evidence that even at that early stage, antihypertensive drugs should be avoided.

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Tobacco smoke increases the risk of premature labor, which can lead to numerous health problems in infants. Quitting tobacco early in pregnancy can lower this to that of a non-smoker. Other significant risks from tobacco use include low birth weight, problems with the placenta, and sudden infant death syndrome (SIDS). Studies show that prenatal smoking also increases the risk of mouth and lip defects, such as oral clefts.

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Vaccination for measles-mumps-rubella (MMR) is a part of the standard immunization protocol for children younger than three years and is between 88 and 97 percent effective against the diseases. A drop in MMR vaccination rates has led to an increased risk of rubella, which is highly contagious. Pregnant women infected with rubella during the first trimester have a 90% chance of passing it to the fetus, leading to fetal death or congenital rubella syndrome or CRS. Children born with CRS have a host of health problems, including heart defects, autism, and diabetes.

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Zika is a viral infection that comes from being bitten by an infected mosquito. Women who were bitten while pregnant may deliver babies with congenital Zika syndrome, a condition characterized by a unique combination of issues including microcephaly. Other possible complications from this condition include developmental challenges, seizures, and vision problems.

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High Blood Sugar

Statistics from the CDC show that between one and two percent of pregnant women in the US have diabetes, while between six and nine percent develop gestational diabetes. Most women with well-controlled blood sugar can have healthy pregnancies, but uncontrolled high blood sugar places the fetus at risk for birth defects and labor complications. Maternal high blood glucose can cause congenital disabilities that affect many organs, including the spinal cord and heart. Labor complications can arise from preterm labor, a baby too large for the birth canal, or preeclampsia (dangerously high blood pressure in the mother).

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Iodine Deficiency

T4 or thyroxine is a thyroid hormone that plays a significant role in fetal development and is essential for normal brain development before and after birth. Maternal iodine deficiency reduces T4 levels and causes changes in parts of the fetus' brain, such as the cerebellum, which can result in congenital deafness and mental disability.

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Lithium is a medication for people with bipolar disorder. Pregnant women who use the drug during their first trimester risk having babies with Ebstein's anomaly, a malfunction of the valve between the two right heart chambers. Ebstein's causes blood to leak back into the heart, leading to congestive heart failure. Though lithium's teratogenic tendencies are well-known, pregnant women with bipolar disorder may not have another viable medical alternative.

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