The first trimester is a period of intense growth for the unborn baby as every major body system, including neurological, circulatory, and skeletal, are developing. Because these important systems are forming in the first trimester, unborn babies are most susceptible to harm during this time. You can protect your unborn baby by avoiding substances such as alcohol, drugs, certain medications, and illnesses such as rubella (German measles). These harmful substances are called teratogens, which are agents that can cause a birth defect. A teratogen is usually something in the environment that the mother may be exposed to during her pregnancy.

The following information discusses ways to avoid some of the most common and most harmful teratogens:

Alcohol consumption by a mother is a leading cause of preventable birth defects, as everything a mother drinks also goes to her unborn baby. Alcohol is broken down more slowly in the immature body of the unborn baby than in an adult's body. In addition, the risk of miscarriage increases with alcohol consumption. It is best to completely avoid alcohol during your entire pregnancy.

Smoking can be damaging to unborn babies in several ways, including increasing the risks of birth defects, low birthweight, preterm birth, and stillbirth. Women who smoke during pregnancy may also be at increased risk for placental complications, preterm labor, and infections in the uterus. In addition, even if you do not smoke, you may be exposed to secondhand smoke in the household, workplace, or in social settings, which also puts you and your baby at risk.

Always check with your physician before taking any prescription or over-the-counter medication, especially in the first trimester. If you take medications for a pre-existing medical condition, such as epilepsy, high blood pressure, anxiety, or depression, you should check with your physician before continuing to use that medication while pregnant.

The effects of illegal drugs, such as cocaine, can be devastating to an unborn baby. Most illegal drugs, including marijuana and cocaine can cross the placenta. If you use such drugs, seek help immediately. If a woman stops taking illegal drugs during her first trimester, she increases her chances of having a healthy baby.