Repeated miscarriage

I’ve had 2 miscarriages in 2018, and one in 2017. I’m now pregnant again and scared this will also end in a miscarriage. I do have 2 live children I had before any of the miscarriages. All my miscarriages happened at around 7 weeks exactly. Anyone know why they all ended the same weeks. Or anyone go through this to have a healthy pregnancy after 3 miscarriages?