Fertilization. An embryologist (a scientist who specializes in eggs, sperm, and embryos) will examine your eggs before combining them with your partner's sperm and incubating them overnight. Fertilization usually happens during this time, but eggs that aren't normal may not be fertilized. (If sperm quality is poor, or if fertilization was unsuccessful during previous IVF cycles, your doctor may recommend using a technique called intracytoplasmic sperm injection (ICSI). With ICSI, a single sperm is injected directly into each mature egg.)
Success varies with many factors. The age of the woman is the most important factor, when women are using their own eggs. Success rates decline as women age, specifically after the mid-30’s. Part of this decline is due to a lower chance of getting pregnant from ART, and part is due to a higher risk of miscarriage with increasing age, especially over age 40.
Luteal support is the administration of medication, generally progesterone, progestins, hCG, or GnRH agonists, and often accompanied by estradiol, to increase the success rate of implantation and early embryogenesis, thereby complementing and/or supporting the function of the corpus luteum. A Cochrane review found that hCG or progesterone given during the luteal phase may be associated with higher rates of live birth or ongoing pregnancy, but that the evidence is not conclusive. Co-treatment with GnRH agonists appears to improve outcomes, by a live birth rate RD of +16% (95% confidence interval +10 to +22%). On the other hand, growth hormone or aspirin as adjunctive medication in IVF have no evidence of overall benefit.