Number of oocytes retrieved and resulting pregnancy. Risk factors for ovarian hyperstimulation syndrome

To test whether the risk of developing clinically significant ovarian hyperstimulation syndrome (OHSS) is related to the number of oocytes retrieved by puncture and the resulting pregnancy and to determine the most suitable cutoff limit of the number of oocytes in predicting OHSS.

The study included 973 patients who underwent ovarian stimulation for in vitro fertilization or intracytoplasmic sperm injection. Using the classification of Schenker and Weinstein, we identified patients who developed moderate and severe OHSS. By multiple logistic regression we established the risk of moderate or severe OHSS development in relation to the number of oocytes retrieved and the resulting pregnancy. A receiver operator characteristic curve was constructed to describe the relation between sensitivity and the false positive rate for the number of oocytes retrieved in the prediction of OHSS.

We identified 35 (3.6%) patients who developed OHSS, 8 (0.8%) severe and 27 (2.8%) moderate. The risk of developing OHSS increased with the number of oocytes retrieved (odds ratio = 1.14) and with pregnancy (odds ratio = 1.14). The most suitable limit for predicting OHSS was 10 oocytes, with 81.9% specificity and 48.6% sensitivity. The risk of OHSS development in cycles with < or = 10 oocytes and no conception was 1.31% and, with conception, 5.12%. The risk of OHSS development in cycles with > 10 oocytes and no conception was 4.43% and with conception, 15.93%.

The risk of OHSS development increases with the number of oocytes retrieved and with pregnancy. The most suitable limit for predicting OHSS is 10 oocytes; however, due to low sensitivity, it is also necessary to consider other factors when establishing the increased risk of OHSS.