Intrinsic fertility of human oocytes.

OBJECTIVE To study the intrinsic fertility of the human oocyte. DESIGN A large retrospective study of natural cycle single embryo transfer (ET) IVF cycles. SETTING Private IVF clinic, university, and private hospital. PATIENT(S) Patients were enrolled consecutively over an 8-year period in a single ET natural cycle protocol. INTERVENTION(S) A total of 13,949 oocyte retrievals with natural IVF single ET. Software package R (version 3.2.5) was used for statistical calculations. MAIN OUTCOME MEASURE(S) Live baby rate per oocyte according to age. RESULT(S) A total of 14,185 natural cycle oocytes resulted in 1,913 live babies from single ET. The number of oocytes required to make one live baby in this large series varied with the age of the female partner. For those under 35, the live baby born per oocyte was 26%. For over age 42 it decreased to 1%. These results fit very robustly with a logistic function curve, which is at first steady (horizontal), followed by a linear decline after age 35 with a 10% loss every year until age 43, and then a flattening out (horizontal) by age 44. CONCLUSION(S) The intrinsic fertility per oocyte in natural cycle is far greater than reported in hyperstimulated cycles, varying robustly from 26% to 4% with age from <35 to 42 years. The curve is relatively flat until age 34, and then declines rapidly 10% per year thereafter.