The success rate of IVF depends on a number of factors, the most important of which is the woman’s age. It is also important to realize whether a cli ic is referring to a pregnancy rate as confirmed by a Beta HCG test or a live birth rate. In the U.S., live birth rates are usually referred to. According to The Society For Assisted Reproduction Technologies (SART), the averagelive birth rate in the U.S. is: 40% for women under age 35 38% for women ages 35 to 37 29% for women ages 38 to 40 19% for women ages 40 to 42 9% for women over 42