I could write this crappy story. I'll tell you exactly what is going to happen. Mary will come back from this weekend pregnant. She will decide to keep the baby but not marry the guy. She will be a modern woman and parade her bastard child all around Downton Abbey and right under Edith's nose and Edith will go off the deep end.
Seriously though, why is birth control such an important plot point to take up three scenes in one episode? (Mary urges Anna to buy it, Anna buys it, Anna tells Mary it is packed specially in her suitcase). Birth control will feature heavily in upcoming episodes. Are the Lord and Lady Catholic or Protestant?
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.