How does lack of parental care harm a child of a teenage pregnancy?

>risk for both. Absence of prenatal care puts mom & baby into the risks of pregnancy before 1900 when childbirth was a leading factor in maternal death. Teens have >risk of toxemia in pregnancy, (>bp+seizures), some types of birth defects etc. Absence of prenatal care >risk of avoidable baby complications and complicated birth. Advanced medical care during labor/delivery or later may not save you from bad choices.
Problem. Unexpected pregnancy is always a family problem. Teenager is not prepared to become a parent, she is still growing up , going to school and let the mother take care of the child.Unhappy parents learn to accept the situation and do the best they can. A lot of counselling is needed.