We often have parents asking this question. It is a bit more complicated than just your BP, and there is not one set number, as every situation is a bit different. We can tell you the general guidelines, though.
If you have just two readings over 140/90, either number, that can count as a gestational hypertension diagnosis. If your numbers are over 140/90 but under 160/110, and everything else is good with you and baby, they recommend 37 weeks for delivery (it may vary a bit by country).
If you have those two high readings over 140/90, but not at 160/110, plus one other diagnostic criterion, usually protein over a certain point, that can count as a preeclampsia diagnosis, and if all else is well with you and baby, 37 weeks is recommended again by all major world health advisory groups.
If you have chronic hypertension, meaning your BP was elevated before pregnancy or in the first 20 weeks, they may not be as concerned about 140/90 and may wait until 38 weeks or longer to deliver, if you and baby are otherwise stable.
If you develop severe features of preeclampsia, such as BP over 160/110, then 34 weeks may be recommended. Other severe features such as elevated liver enzymes, signs of kidney struggle, and evidence of brain swelling such as severe and unresponsive headache, often mean delivery earlier than 37 or even 34 weeks (often within hours to a couple of days at most). HELLP Syndrome, with or without high blood presure, usually means delivery within hours to a couple of days at most. With severe features or HELLP, they may delay delivery for a short time in order for steroids for baby's lungs to take effect, if they feel that is safe in that specific situation, while watching closely in case anything changes to necessitate an expedited delivery.
Eclampsia (seizures) usually means delivery very quickly once you are stable.
If baby is showing signs of struggle due to an insufficient placenta, such as low fluid, poor growth, or poor blood flow through the cord, then they may decide to deliver earlier than 37 or 34 weeks.
It is all a balancing act. They don't want you to get too sick, and there can be a point at which baby is not doing well on the inside either, but if both of you are doing okay, they will plan for 37 weeks. If one of you starts to show signs of bigger issues, then they will deliver sooner.
You can have BPs just over 140/90 and be stable enough to wait for 37 weeks, or you can have BPs just over 140/90 and be very sick and in need of early delivery if you have something else turning severe like liver enzymes. It is a bit complicated, so someone else's BPs won't really tell you much.
What you can do is talk to your doctor about your numbers and ask what their concerns are. You can ask how they will be monitoring for signs of severe features too. Once you have a gestational hypertension or preeclampsia without severe features diagnosis, they typically keep a very close eye on you and baby with blood work and ultrasounds frequently so you can ask about that sort of thing.
I hope this helps explain all of what your doctors are considering when they decide that you are safe to remain pregnant longer or that it is time for delivery. They are doing their best to find the right balance in order to keep two patients safe.