(So first of all I play with german translation of all the nraas mods I have installed so I don‘t know exactly how the options are called in english version but I hope I‘ll translate them correctly.)
At the beginning of a new game (I play in Twinbrook) I created some new townies and my family so my start-population was 100 sims. I set the chance of unexpected pregnancy to 90 and the base amount of children(?) to 10. I changed a few other things but they aren‘t related to pregnancy. My townies were having even 5 babies a day until a sim-week ago all pregnancy and birth related notifications stopped. I googled the problem and found that maximum population is by default set to 150 - at this point I had 152 sims in town including my own 6 sims. I changed it to 0 but after 3 days nothing happened, so then I changed it to 500. Still nothing. Only one household has 12 sims, the rest has 1-7. Right now I have no infants and no toddlers in town. Other options (marriages, breaking up, deaths etc.) are working. I‘m not sure what should I do? If it matters the other settings I changed are:

• married sims choose the husband‘s surname
• maximum amount of pets in family to 12
• and maximum amount of sims in a household to 15

First you have far too many sims, this will may lead to performance problems, it's ok for your active household, but so many residents?
Are you doing a challenge?

Babies need cribs I think, and also beds for all sims in every house? Homeinspection on?
I also think under general - pregnancy there is a cool down between pregnancy option, default is 3 days.

Ich bin leider gerade nicht im Spiel,

Info: Ich weiß nicht welche Übersetzung du hast, aber ich empfehle dir, für alle nraas mods die du hast, jede manuell zu aktualisieren. Diese Updates sind leider noch nicht in den mods drin.

post89672#p89672

All of the houses in town are likely occupied, and SP will not push households to have children if they don't live in an appropriate home.

An increase of population by 50 also sounds like unbalanced lifespan vs progression settings, the population of the town needs time to fluctuate- for the population to grow up and for elders to pass away. It is normal for there to be birth and death waves, as long as the population can handle it.

And as C-Dark has said, 150+ residents is more than the game is meant to handle. Changing the limit doesn't mean your computer nor the game engine can keep up with simulating that many at once and eventually everything that SP is trying to push sims to do may come to a halt.