There are not that many frum people, and there are not that many frum girls who get married AND have kids at nineteen. I have two cousins who got married at nineteen and neither one is a “teen mom” (one doesn’t yet have kids, one just had a baby at 21). The chances of frum people skewing the statistics is very, very small.
Sure let’s say you know ten people like that (and that’s just you- I’m sure there are more)- however, according to the CDC, 329,797 live births were recorded for girls ages 15-19. There is NO WAY that a couple thousand frum girls are skewing the data.
(The number of teen pregnancies in the US is actually shrinking by many percentage points a year, interestingly enough- over the past 20 years, the rate has dropped by 20% and the number is at its lowest point since records began to be kept.)