Darkness of test line

currently 13dpo (had an IUI on 4/20). 
Below are my tests from the past three days 11-13dpo/IUI). The bottom one being the most recent.
I know you're not supposed to over analyze the darkness of the test too much but the most recent one is slightly lighter. Hopefully nothing to worry about?
 I will go in on Tuesday morning to have a beta blood test done. Wish me luck! We've been TTC for 1 1/2 year (both 29, slight male factor motility issue). Had an early miscarriage almost exactly a year ago, so really hoping this one sticks. 
Goodluck to everyone this month!

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