Everywhere you look the statistics are the same. Less and less children are being born, and fertility rates are dropping as well. I am not a biologist, so I cannot tell you if there is a relationship, or what it might be. I can, however, tell you something significant. As the world continues to refuse to have children, and many of those that are conceived by pagans are murdered before they are born (Lord have mercy upon us!), we are called to continue in faithfulness.
In other words, Catholics need to continue just to be faithful and have as many children as they are able to. Raise them in the faith and prepare them to stand in the gap when the rest of the world goes sideways. Worse case scenario? The pagans will diminish down to an imperceptible number, and Catholics will breed them out of existence just by sheer numbers.
It is truly remarkable that the large majority of Catholics who are seeking traditional reverence in the Mass, are also seeking to have large families. God set this up, and He is going to use it. Every one of us has a part to play in this. Let us all support one another in the raising of the next generation, that they would be faithful and devoted to the Lord Jesus, His Mother, and the One, Holy, Catholic, and Apostolic Church.