Pregnancy rate in IVF patients with unexpected poor response to ovarian stimulation.

Objective: To evaluate whether an unexpected poor response (cases with ≤3 oocytes) leads to a reduction in the pregnancy rate in IVF cycles compared to a suboptimal response (controls with 4-9 oocytes) in women with adequate ovarian reserve.

Methods: A nested case-control study performed in a retrospective cohort of couples undergoing IVF at the Infertility Unit of the ASST Lariana. Cases and controls had adequate ovarian reserve and were matched 1:1 for female age and number of previous cycles. Cumulative clinical pregnancy rate per oocyte retrieval was the main outcome.

Results: Overall, 113 cases and 113 matched controls were included; the median number of available oocytes was 2 and 6, respectively. The cumulative pregnancy rate per cycle was significantly reduced in cases compared to controls with a crude odds ratio = 0.45 [95% Confidence Interval: 0.28-0.82]. A binomial logistic model indicated that an increase in one oocyte increases the odds for cumulative pregnancy rate per cycle by 1.27 in women with 9 oocytes or less. The cumulative pregnancy rates per cycle in cases and controls, according to female age were respectively: 29% versus 54% in patients aged <35 years ( = 0.036); 22% versus 43% in patients aged 36-39 years ( = 0.048) and 11% versus 13% in patients 40-45 years old ( = 0.72). Patients belonging to older age groups showed decreasing probability of cumulative clinical pregnancy rates both among cases and controls group ( < 0.05).

Conclusions: The number of available oocytes significantly affects the probability of success in IVF cycles with unexpected impaired ovarian response.