If you and your doctor decide on the procedure in a natural cycle (or as it is called in medical terminology a modified natural cycle – since one drug is given, i.e. hCG injection), the first follicle ultrasound exam should be performed between days 6 and 10 of the cycle. The day of the first ultrasound depends on the length of your cycle, your age and expected time of ovulation. Follicle growth should be monitored, and when the follicles reach 14-17 mm in diameter you will be given a hCG injection. Sometimes a doctor may require blood tests to determine your estradiol or LH level prior to injecting hCG, in order to ensure ovulation has not yet begun. Ovulation should take place 36-38 hours after a hCG injection. Insemination or follicular aspiration is planned 1-2 hours before that period has expired. If IVF/ICSI is planned, an ultrasound exam is usually carried out immediately prior to follicular aspiration, in order to ensure a follicle has not ruptured.