The ovulation inducing substance (ovitrelle or pregnyl) has to be taken exactly 36 hours before the planned oocyte pick-up. If you take it too early, ovulation will already have occurred when you arrive at the clinic. If you take it too late, the oocytes will not be ready for aspiration. In case you have forgotten to take the ovulation induction, please call us directly and ask for instructions. Often, it can be done 24 hours later.