Hi!
I've been trying to find this book to no avail. It's a modern romance novel, and might be part of a series. The heroine is around 30 years old. At the beginning of the book she goes to the doctor's to have a PAP-test - this may (or may not, I'm not sure) happen on her birthday, and the doctor (who is her brother-in-law) makes a joke about her eggs getting old. Later in the book she marries (or just gets engaged) to an English man (maybe he is her co-worker, they both teach at University), who is about to be forced out of the country because he doesn't have a green card. They go live together and there is a scene with a woman sent to make a surpise visit to them to make sure they're a genuine couple.

It's muddled, I know. Whatever is written in brakes I'm not sure about; the rest, I remember. I hope you can help!

I found it on my own! It's "The Perfect Match" by Kristan Higgins, book 2 of the Blue Heron series.
In the very first chapter, the heroine has a pap test on her 35th birthday, and the doctor, who is her sister's ex boyfriend (not her brother-in-law, as I wrote above...), does make a comment about eggs getting old
I'm off to re-read it, just to see if I remembered any other details or not...!