Sometimes, patients who go through ovarian stimulation and IVF do not respond well. These patients have low estrogen levels, few eggs retrieved, and fewer embryos to transfer back to the uterus. Overall, they have lower pregnancy rates than other patients. It is not clear which medication protocol would give them the highest chance of pregnancy. Two protocols, one called the "E2/antagonist" protocol and the other called the "OCP/microdose" protocol, are routinely used in poor responder patients. But, they have never been prospectively compared so it is not possible to say whether one approach is better.