Hi Liz,
Welcome to Catholic Answers! I hope you find your time here to be edifying and interesting.
I’m sorry that your MIL is nagging you. If my MIL were nagging me about having kids I’d feel terrible, since we just haven’t been blessed with kids yet. But let’s try to give your MIL the benefit of the doubt. If she’s a devout Catholic, she’s probably more concerned with possibility of her son and daughter-in-law using contraception than with their decision to postpone having children. The Church teaches that couples can licitly decide to postpone having children if they have just reasons, but they may never contracept. Withdrawal, which is what you’re encouraging your husband to do, is considered a grave sin. Sex is meant to be open to life and any attempt to frustrate that openness (by taking a pill, wearing a condom, or pulling out, etc.) is wrong. Since most Protestants don’t have a problem with contraception, your MIL probably assumes that you are contracepting (which you sometimes are) and is likely worried for the state of your souls.
Have you heard of natural family planning? NFP is an umbrella term for a variety of methods of planning or preventing pregnancy based on observing naturally occuring signs and symptoms in a woman’s body. Couples wishing to avoid pregnancy abstain from sexual intercourse during the woman’s fertile period. Practiced correctly and consistently, it is as effective as the Pill and certainly much more effective than withdrawal. Catholics may use NFP because in choosing to abstain during fertile periods they aren’t deliberately frustrating the marital act. (Some may see this as splitting hairs, but the difference between NFP and contraception is huge, and I’d be happy to elaborate if you wish). There are additional benefits as well; couples practicing NFP learn self-discipline and grow in respect and love for each other. They develop better communication skills since NFP requires that spouses be on the same page as each other. Studies also suggest that couples who use NFP have a lower divorce rate than couples who contracept.
I’d encourage you to continue to pray about whether or not you should be postponing children right now. When I got married I had two semesters of my Masters left too, but we decided that we would not to try to postpone pregnancy. (Btw, seven months and one miscarriage later, I’m still not pregnant). We made this decision in light of our understanding that one of the primary purposes of marriage is to have a family, and that the world greatly underestimates the joy and blessings of having children. I struggled with that too, because I think I would also enjoy a career, but I really believe that if God blesses us with children, raising them will be as challenging and rewarding as working outside the home. If you do decide to postpone, consider learning a method of NFP, like the sympto-thermal method
ccli.org/ or Creighton
creightonmodel.com/.
If you learned and practiced NFP, you would then be able to truthfully tell your MIL that you and your husband are not contracepting (it might put her at ease, even if it isn’t any of her business) and could gently remind her that the Church permits couples to discern for themselves whether they have just reasons to postpone children.
Blessings on you and your husband. Good luck finishing your Masters!