"If Jennifer wants to reduce the risk of having a baby with a birth defect caused by an environmental substance like drugs or alcohol, she should understand that exposure to teratogens can cause the most damage during?"

Jennifer should understand that exposure to teratogens can cause the most damage during exposures such as the duration of exposure, the amount of teratogenic substance, and the stage of development the embryo or fetus is in during the exposure.

Explanation:

Teratogens may affect the embryo or fetus in a number of ways, causing physical malformations, problems in the behavioral or emotional development of the child, and decreased intellectual quotient (IQ) in the child. Additionally, teratogens may also affect pregnancies and cause complications such as preterm labors, spontaneous abortions, or miscarriages. Teratogens are classified into four types: physical agents, metabolic conditions, infection, and finally, drugs and chemicals.

DURING THE EMBRYONIC PERIOD.

Explanation: Teratogens are agents which can cause a birth defect. They are usually something in the environment that the mother may be exposed to during her pregnancy. Teratogens could be a prescribed medication, a street drug, alcohol use, or a disease present in the mother which has the tendency to increase the chance for the baby to be born with a birth defect. About 4 to 5 percent of birth defects are caused by exposure to a teratogen.

When a baby is developing, there are certain organs of the body forming at certain times.

If a teratogen has the potential to interfere with the closure of the neural tube, for example, the exposure to the teratogen must occur in the first 3.5 to 4.5 weeks of the pregnancy (Embryonic Stage), since this is when the neural tube is closing.

Most teratogens are harmful only during a critical window of development example thalidomide (cancer drug) is teratogenic only between days 28 and 50 of pregnancy.

Teratogenic agents inhibit specific receptors or enzymes or disrupt specific developmental pathways example some agents show neurotropism or cardiotropism.

oxygen +1 most likely