Usually they find it later on in pregnancy.
I found out about my high bp when I was about 5 weeks prego, but I am also a high risk pregnancy. They monitor all these things through out and if u get red flags drs should take precaution and have u tested
In the UK we get blood tests in the beginning quite often, we have weight urine and blood pressure checked every midwife and consultant appointment. I've had gestational diabetes. They tested for it based on the fact that I have polycystic ovary syndrome which makes you at risk of gestational diabetes x
Ps if you're not having symptoms, attending doc appointments and theydont seem concerned try not to worry