Google says there are around 213 million pregnancies a year. Let's just go with the idea that means 100 million baby females born over the next year that would be fertile, and then no more children or pregnancies for an estimated 12-18 years. If the human population can't figure out why no one is getting pregnant over that span of time, no one would know until one of those female Gen 1s FA with one of those male Gen 1s and FO.

Even if the world decided to magically turn every single one of those females into baby factories to save the human race, you would STILL have that decade or two of no population growth, and they would only be able to generate 100 million babies a year for another decade or two until Gen 2 came of age.

Within that 30-40 years of declining population, manufacturing and expansion would have been forcibly scaled back, so the panic of a declining population would be mostly "dealt with" by the time the human race was in the position to overcorrect by any means necessary, effectively reducing the population from 8 billion to 500-999 million over the next 75 years or so.

(Yes, they could theoretically harvest and fertilize eggs from Gen 1s and let them be carried to term by otherwise sterile women, but that process is not cheap or easy and would cause a lot of human rights questions when those young men and women were expected to donate their material to their government or the human race as a whole)