Recurrent Pregnancy Loss

So, my sister keeps having recurrent pregnancy loss. Her first ever pregnancy was back in 2012 and she went full term and had my niece in 2013. She then had a miscarriage with a different man in 2015. She then met her husband in 2016 and they have had 6 miscarriages since then. The longest she ever got to in pregnancy was 10 weeks. The rest of the miscarriages have been happening around 6-8 weeks.

She has had blood test done and is fine there. But that’s the most she has had done. He hasn’t done anything to get checked himself. She’s 28 and he’s 32.

So, all in all, she’s had a total of 7 miscarriages and hasn’t went full term since her first pregnancy.

Has anyone been through this? If so, what did you do about it? Or who does my sister need to see to get answers, because her OBGYN didn’t do much for her but blood tests?

I looked online and it says that the main cause of miscarriages in general is due to abnormal chromosomal abnormalities. But I just wish I understood more about recurrent pregnancy loss.