Yes, one of the gifts we have is self-control. However this self control is not meant to keep married couples from having sex. God created sex to be done within marriage, as wild and crazy as the couple wants. He wants us to have sex. Witholding sex from your spouse should not happen within marriage. This self-control the bible speaks of is to be used when we speak, how we act around others, not to keep us from having sex with our spouse.
You do have to remember to take the pill every day. Some people set reminders, my brother helps his wife remember, I take mine at bedtime every night. We keep track of the amount of condoms we have on hand, making sure to not run out. Not having children is what we want as a couple, so we do what we need to make sure that happens. Children are not bad, but they are not meant for everyone.
Of course your spouse could die before you. I dont want to have children for the purpose of having someone take care of me or be around me...that would be selfish. Also, many children move away from their hometown and will not stay around to take care of parents, some dont even give a crap about their parents. If we chose to have children, it would be because we want to share our love with a child, because we have something to give, not because we want someone to take care of us.
Having a PhD does not keep someone from being a parent. However, if I decide to do that, I will need to have lots of time to spend on research and studies...time I would have to pull from not only my husband but children as well. Not fair to them. After graduation I would be 40...and would need to find a full time job to make all the time, money, and effort worth it. Again, lots of time spent away from my child. With missions, we want to do missions in the more dangerous areas of the country. So bringing a child into that would be dangerous as well. If you have family nearby, who is willing to help with whatever you need, then yes...use that resource. But not everyone does. For example, my parents are 6 hours away. His is 12. His brother is 9 hours away, mine is 7. Family is not close enough to help us. You need to be the one raising your child, not a stranger. You make the decision to bring a child into the world, you should take care of it. If you need help, seek that. But other than a spouse, your new priority is this child.
If you desire children, then you would find or do whatever you need to make it happen. However that is not our desire. Our focus is each other and our careers. If you have health issues, and you want children, then you can find someone to help you out with that. And you are right on the goal of an OB. But again, that is not our goal.
If that is what you wanted. I am already married, and these education goals came after marriage with a very supportive husband. It is very very difficult to be married and in school at the same time. You have to make time for your spouse, and work hard enough to pass your classes. It can easily cause problems in a marriage and I always encourage people, young people, to wait until they are out of college before getting married for that reason.