The placenta produces human chorionic gonadoptropin, or hCG, during pregnancy to increase the lining of your uterus so your baby can implant there. It is also responsible for producing progesterone, which will eventually take over the job of maintaining your corpeus luteum, the lining of your uterus. HCG also has properties that trigger your ovaries to release eggs, thus the name "trigger shot" for an injection of the synthetic form of this hormone that will prompt ovulation.
Synthetic hCG is marketed under the brand names Novarel, Pregnyl, Ovidrel and Profasi. The website TwoMommys.com indicates that the average cost per injection is between $35 and $75 and that some health insurance companies cover the expenditure.
Trigger shots can narrow down your best time for conception. Even if your aim is natural conception as opposed to intrauterine insemination or in vitro fertilization when timing is most crucial, an hCG trigger shot might be recommended if you don't ovulate or if you have irregular periods, making it difficult to know when or even if you are fertile.
The process of an hCG trigger shot begins three days after your period starts, according to the Advanced Fertility Center of Chicago. Most controlled ovarian stimulation cycles start with the injection of follicle stimulation hormone–FSH–at this time. FSH spurs your ovaries to begin developing eggs. You will continue to receive FSH shots over the next week or so and your doctor will monitor the progress of your follicles. A series of transvaginal ultrasounds will allow your doctor to know when your eggs are mature. Each follicle should measure between 16 and 20 mm for optimal ovulation. Then an hCG shot will trigger your ovaries to release those eggs.
When your follicles are ready, your doctor will send you home with an hCG injection that you can either administer yourself or have your partner administer for you, either intramuscularly or subcutaneously, according to JustMommies. Your ovary should release its eggs within 36 to 46 hours after you take the hCG shot, according to the Advanced Fertility Center of Chicago. Your doctor will tell you exactly what time to take the shot, especially if you are undergoing an IUI or IVF when your doctor will need to know exactly when you are likely to ovulate in order to schedule the procedure. If you are trying for timed intercourse, the Advanced Fertility Center recommends the morning on the second day after you received your hCG trigger shot.
TwoMommys.com reports that some women experience headaches, fatigue, sore breasts, abdominal discomfort, irritability and water retention just after an hCG trigger shot. Unfortunately, these are also signs of early pregnancy and there's no way to tell for approximately two more weeks which is causing the symptoms.
Fertility Today advises waiting to take a pregnancy test until at least 10 days after you receive the trigger shot. Pregnancy tests measure for natural hCG in your urine, which occurs after you conceive. There is no way to differentiate between the synthetic hormone you were given and the real thing, so you'll have to wait for the synthetic hCG to dissipate from your system before a pregnancy test will be accurate.