It depends on the age of the patient. Unknown sterility implies that a couple has tried to get pregnant for at least 1 year without results and has done a basic infertility study which results in all values within normal range (hormones, ultrasound, seminogram, tubal permeability).
In these cases, if the woman is under 37-38 years of age, she can begin by artificial insemination 3-4 attempts (possibility of gestation of 15% for each attempt) vs. IVF (possibility of gestation of 50%).
In situations of patients of 38 years or more it is not recommended "to lose time" and, for this reason, it is indicated to make directly an IVF that will contribute a better rate of pregnancy in the smaller possible time and the possibility of leaving some embryo vitrified in case later the couple decided to extend the family.
Suggested for you: What Is Unexplained Infertility? – Causes, Diagnosis & Treatment.