Dear Mr./Ms. Bossname,
I’m pregnant! You have been so supportive of my family’s goals since day one at XYZ Company that I wanted you to be the first to know. As planned, I will now be resigning. I’m happy to stay on until the end of the month if you’d like.
I can’t tell you how much I value the opportunity to work for a company that offers benefits to part-timers, and that the coverage includes IVF treatment. I have been struggling with infertility for so long, but could not afford the procedures until joining XYZ.
As much as I know you appreciate my transparency about joining XYZ for the IVF benefits, please know that I equally appreciate your understanding that I will now be leaving. Thanks again.