The efficiency of the human oocyte after ovarian stimulation.

Introduction: Live birth per cycle and live birth per embryo transfer are commonly
used outcome measures for in-vitro fertilization treatments. By contrast,
the evaluation of the reproductive efficiency of human oocytes fertilized in
vitro is seldom performed on an egg-to-egg basis. This approach of evaluating reproductive outcome may however gain importance due the foreseen wider
use of oocyte cryopreservation, as the technique is becoming more established.
The aim of the current study is to quantify the reproductive efficiency of the
oocyte according to ovarian aging and ovarian response.
Methods: The current analysis is based on all consecutive ICSI data, collected
prospectively over a period of 18 years from 1992 until 2009, and stored in the
database of our academic reproductive medicine centre. Only ICSI cycles were
included in order to have the opportunity to examine mature oocytes. The outcome
of primary interest was oocyte utilization rate, computed as the number of
live births per mature oocyte retrieved, and expressed as a percentage. Oocyte
utilization rates were calculated by age at oocyte retrieval, starting at age 23
and stopping at age 43, and by ovarian response, categorized in three mutually
exclusive groups (1-5, 6-10, or 11or more mature oocytes). Multiple regression
modeling was used to quantify the independent impact of age and ovarian
response on oocyte utilization rate.
Results: The current analysis reports the outcome of 207.267 oocytes retrieved
in 23.354 ovarian stimulation cycles performed consecutively in a single centre
over an 18-years period from 1992 until 2009. Overall, 3.83% of aspirated
mature oocytes resulted in a live birth. The oocyte utilization rate between the
age of 23 and 37 remained fairly constant, with a mean of 4.47% live birth per
mature oocyte (95% CI, 4.32 to 4.61). In this 23-37 years age group the oocyte
utilization rate was highly dependent on ovarian response: compared to the referent
ovarian response group with 11 or more mature oocytes, the oocyte utilization
rate was 1.7% higher in the response group with 6-10 mature oocytes,
and 2.8% higher in the response group with only 1-5 mature oocytes, with absolute
rate differences adjusted for age of 1.6% (95% CI, 0.9 to 2.4%; Pand 2.8% (95% CI, 2.1 to 3.5%; Ponwards, a significantly lower oocyte utilization rate was noted, declining from
3.80% at the age of 38 to 0.78% at the age of 43 years old (P38-43 years age group, oocyte utilization rate was no longer dependent on ovarian
response rate (P = 0.87).
Conclusions: The study shows that the live birth rate per oocyte and the number
of oocytes per live birth remain remarkably stable between the age of 23
and 37 years. A marked decrease in oocyte utilization rate is observed from
the age of 38 onwards and a dramatic drop is seen after the age of 40 years.
Between 23 and 37 years of age oocyte utilization rate depends largely on ovarian
response and to a much lesser extent on age. From the age of 38 onwards,
on the other hand, utilization rate depends largely on age and to a much lesser
extent on ovarian response. In view of recent studies reporting pregnancy rates
from cryopreserved oocytes comparable to those achieved following fresh IVF,
these data provide information on the expected outcome in women undergoing
fertility preservation. Moreover, considering the time delay between oocyte
harvest and the effective use of cryopreserved oocytes in clinical practice, it
is crucial to provide precise estimates for the number of oocytes needed to
achieve a live birth.