For those of you who aren’t familiar with the HCG (human chorionic gonadotropin) trigger shot, it is a single dose intra-muscular shot given 36 hours before egg retrieval to help mature the eggs. Because this shot is made of HCG, the pregnancy hormone, it makes at home testing tricky.
If you test too early on a non-triggered cycle you won’t have any HCG in your system and so you’ll get a BFN. If you test early during a triggered cycle you may see a line on your pee stick that is just from the lingering trigger and not from a burrowing baby.
This potential false positive scares me. It scares me enough that I worried about it for other people when we were still trying au natural. I’d look at other girl’s peesticks and roughly calculate how much HCG should be left and if it might be a false BFP.
If you can’t tell I’m kind of a worrier.
One of the first things I did when I got my IVF 1.0 calendar was create and excel trigger ½ life calculator based on a 10,000 unit trigger shot and the average ½ life I was able to find on the manufacturers web site. Of course, since last cycle was cancelled I never used it.
Today I opened the spreadsheet and realized I’d used overly simple logic and I knew that would bother me. I had used linear interpolation to estimate the amount of trigger left when the equation is clearly exponential and to a math nerd like me that is very irritating.
So I rebuilt it.
I plotted the half life, 29 hours (with a confidence interval of +/- 6 hrs) and found the equations for each using a trend line. Excel is a very smart tool and did all the work for me. Now I have a fabulous calculator which allows me to enter trigger dosage and number of hours since injection and outputs the low, likely and high residual HCG in my system.
Have I mentioned I’m a huge nerd?
If anyone would like a copy of the file (which also has a beta doubling time calculator) just send me your email address and I’ll send it on over. If I get bored tomorrow or have any requests I’ll add on a booster shot function.