i of course dont have the injection myself, but cant help my worries about contraception.

my girlfriend can be quiet selfish at times so im here to get my own answers.

if she happens to get pregnant and then gets the injection after (maybe we dont realize shes pregnant) what will happen, ive heard it kills the fetus/gives wrong pregnancy test readings etc?

im persuading her to to have a quick pregnancy test when shes getting the injection just to make sure, but would the injection itself from the previous month make the test inaccurate?

all answers are appreciated, Dave