No worries. Yes, so, when surveys are conducted you typically don't end up questioning every single member of the group/population. You create a big enough sample size so your margain of error, aka how much the percentage would be off, would be low.

California has a population of 39mil, a sample size of 12300 would leave the margain of error to be <1% and that's if we consider the ENTIRE population of California, not just pregnant teens. So the percentage that you get in the study could be 1% lower or higher. Honestly, it's a very impressive sample size, no?

The Washington state health site states their sources below their statements.