It’s probably impossible for a population to average that rate though.

Takes about 9 months to output N humans where N approaches to 1 on large averages as even twin births are like 1.2 percent.

Also many females cannot be pregnant again for a while after giving birth, even if we had sped up the pregnancy.

To average 6 babies, we need something like giving birth to triplets every 5 months in average, which improbable even if we had the technology, will and the economics that could support this.

But you know, "improbable" is such a funny word, especially out of context :)

It can also be done months faster getting multiple humans though.