The first thing that comes to mind after a worldwide catastrophe is rebuilding. We want to rebuild our homes, rebuild communications, and rebuild a functional, civilized society. We also want to rebuild the population to ensure survival of the human race long-term, right? Wrong!
In the initial stages of life after the SHTF, it might seem logical to do your best to procreate. Lives were undoubtedly lost so the need to create more life is bound to be at the forefront of many minds. Though this is going to be a necessary undertaking at some point, time is of the essence.
Thing about every pregnant woman you've ever known. Many of them were subject to aches and pains. Nausea plagued them frquently. Their feet got swollen. Some even wound up on bed rest. Now, in a changing world where the societal grid has collapsed, if a pregnant woman has medical issues, you cannot exactly run her to the nearest hospital and have her fixed right up. She is going to have to endure that which plagues her, be it good, bad, or indifferent. There will be no ob-gyn to examine her, no ultrasound to check on that baby. All there will be are crossed fingers and hopes for the best.
Something else to consider is the vulnerability of a pregnant woman, and I don't mean crying at the drop of a hat. In a predatory situation where she is the prey, a pregnant woman is less likely to get away. How can she run for her life when her fastest gear is performed in a waddle? Also take into consideration that the weight gain accompanying pregnancy will affect her center of gravity and balance. Even if her body could run fast, it is constantly changing and every new day is a new balancing act, literally, for her. No one is saying pregnant women are helpless, but many of them do require extra care and may struggled to survive in primitive conditions.
All of this may sound harsh, but it must be taken seriously. If the human race is to survive, babies must be born, but in a post-apocalyptic world, the number one thing on the list should not be to breed immediately. Procreating should come in time, once safety and stability is re-established, making it safe to carry a child.
It is hard to bring life into the world when the carrier of said life is fighting to survive herself. Without access to complex medical care and facing a multitude of potential threats on a constant basis, it makes sense to wait to make babies. If condoms are not a part of your BOB or stashed somewhere in your bunker, then you might want to put them there. Just because the opportunity to make a baby exists doesn't mean you should immediately bring a baby into the apocalypse.