Reproductive Systems Gametogenesis and Early Development
In the late 1960s, a drug called thalidomide, ironically prescribed for morning sickness, was responsible for the malformation of several babies. In general, at what time during pregnancy would it be most dangerous to take a drug that is toxic or harmful to the developing child?
|A||During the zygote stage|
|C||During the embryonic stage|
|D||During the fetal stage|
The worst effects of any teratogenic (birth-defect causing) drug would occur during the embryonic stage (week two to the end of month two). This is because all of the major events of organogenesis, germ tissue formation, and differentiation occur during this stage. If the drugs were ingested earlier than implantation (choices A and B), the negative effects would likely terminate the zygote or morula before it could implant, or might not harm them at all, depending on the drug. While drugs can certainly harm a fetus, it is usually less severe because all of the major organs have been formed and the general body layout is complete by this stage (choice D).