Why Does the Woman Taking Oral Hypoglycemic Agents to Control

Why does the woman taking oral hypoglycemic agents to control diabetes mellitus need to take insulin during pregnancy?

A) Insulin can cross the placental barrier to the fetus.
B) Insulin does not cross the placental barrier to the fetus.
C) Oral agents do not cross the placenta.
D) Oral agents are not sufficient to meet maternal insulin needs.