The next step in your IVF treatment is triggering the oocytes to go through the last stage of maturation, before they can be retrieved. This last growth is triggered with human chorionic gonadotropin (hCG). Brand names for this include Ovidrel, Novarel and Pregnyl.
Timing this shot is vital. If it's given too early, the eggs will not have matured enough. If given too late, the eggs may be “too old” and won't fertilize properly. The daily ultrasounds at the end of the last step are meant to time this trigger shot just right. Usually, the hCG injection is given when four or more follicles have grown to be 18 to 20mm in size and your estradiol levels are greater than 2,000pg/ML.
This shot is typically a one-time injection (yeah!). The timing of the shot will be based both on your ultrasounds and blood work and when your clinic schedules your retrieval.
If not enough follicles grow or if you're at risk for severe ovarian hyperstimulation syndrome, your treatment cycle may be canceled and the hCG shot will not be given. If treatment is canceled because your ovaries didn't respond well to the medications, your doctor may recommend different medications to be tried on the next cycle. While not common, a cycle may also be canceled if ovulation occurs before retrieval can take place. Once the eggs ovulate on their own, they can't be retrieved.
Cancellation happens in 10 to 20% of IVF treatment cycles. The chance of cancellation rises with age, with those older than age 35 more likely to experience treatment cancellation.