Thursday, July 28, 2011

Super-Nerd Trigger Calculator

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.


  1. oh i have been googling this all moring. i had 1500 iu then 4 days later had another 1500 iu and now its 7 days past my last booster and wondering if my faint line is a false bfp..aaarrgggghhhh.. so ur not too much of a worrier... your just smart..haha

  2. LOL!! This is awesome! I have no idea what the technical mathematical jargon means, but it sounds smart!! :P

  3. Hey Lindsey,

    It is Jo from Love at move the stars. sorry my email bounced back so putting it out there on here..

    Thank you so much for helping me, you are very clever setting up a formula... i would have no idea where to start.

    so here is my list.

    - egg collection, Friday 19th july

    - first trigger 1500 iu, Tuesday 19th july

    -Transfer of 5day blast,Wednesday 20th of july

    -last booster 1500iu, Friday 22nd of july

    HPT- 27th, 29th and 30th of july all slightly bfp ??? what are your thoughts. let me know if you need any more info. and thanks so much... i think im going to poas everyday from now til bt anyways..haha

  4. I love your nerdiness! I'm right there with you :)

  5. Oh my how I love you! Such a dork! ;)

  6. That is GENIUS!!!!! Want! Want much! meiermadness at gmail dot com

  7. I would love a copy of this if you are still checking this and could send it! amydrossie at gmail dot com.

    Thank you!


  8. Hello- i would also like a copy if you don't mind!! Thanks for putting it together.

    Lelia dot Kate15 at gmail

  9. Did you ever put together a booster shot function?

  10. I am pretty sure I added a booster function. Email me at Lindsey dot L dot hunter at gmail dot com and I'll send it over!

  11. I'm intrigued. I'd love a copy. Amanda1980hoffman at gmail