Theories on phases of development

What are teratogens? Give a brief description of the process by which teratogens affect an unborn baby. Explain specific theories on phases of development that could be applicable in this discussion.

This is what I have so far, but can not pinpoint theories on phases of development.

1.)  Teratogens are considered to be harmful external agents. Male fetuses tend to be more sensitive to them than female fetuses. Teratogens include opioids and alcohol that affect the baby’s chance to survive after birth. One cause of this can be sudden infant death syndrome (SIDS). A baby who is born after having been hosted by a mother who has used alcohol or opioids will have a higher rate and a wider range to have developmental disabilities which include attentional disorders (ADHD) and an autism spectrum disorder. A mother who uses alcohol and/or opioids can cause their child to be born addicted to the opioid or cause them life-long harm by causing them to be disabled or be on the autistic spectrum. They may also face the cause of sudden infant death syndrome. While the fetus is unborn, the effects of the opioids the mother uses also effects the brain development and possible growth of the fetus. This will cause more issues when it comes to being brought into the world, with the previous information provided.