Has anyone experienced placental abruption more than once?

Our first baby died due to heart block and placental abruption at 26 weeks. The first time, I was told the placental abruption came from me having severe preeclampsia. Our second, died at 28 weeks, placental abruption. The doctors are saying they dont really have an idea what caused the second placental abruption. I did not have preeclampsia and was taking aspirin. Both were small for their gestational age. I want to try again, but first losing weight. But Im afraid even then, it'll be the same outcome.

Has anyone else experienced this? Did your doctors find a cause? What did you do different your next pregnancy?