My dearest one, this is only my opinion, it is ONLY a marathon, not a baby, I would say, forget the marathon IF you are pregnant, there are thousands of marathons a year, they are not all that important, I have done 3 of them , please believe me, for have 3 children that are far more pricless than to be able to say I ran the Chicago marathon. Maybe some day after the baby comes you will have an opportunity to run a marathon, with a history of that many miscarriages, I would do all I could to insure a healthy pregnancy & baby, that reward is matchless,& compares to nothing else in life. Maybe 20 years from now my dear one, you will run a marathon with the baby you now carry
God Bless you

there are plenty of runners that keep running through their entire pregnancy and those first few months when the baby is starting to form, many many women don't know they are even pregnant yet so they keep running. Normally, if you are active and a runner prior to pg, then to continue to do so after learning you are pregnant is not a risky thing - so long as you just keep an eye on your heartrate. HOWEVER, you are not "normal" in the sense of women getting pregnant and having healthy pregnancies. I, too, have a history of miscarriage and infertility, so I sort of know where you are coming from. This really is a question for your doc and I'm assuming with 5 m/c's and 15 yrs of trying , you are working with a high risk OB. But, since you do have such a long history of fertility issues and m/c's, then I would err on the side of caution and stop training, unless your OB says it's okay. Your body is a bit more fragile when it comes to allowing the baby to mature past some of these initial stages, so if it were me, I would not want to continue doing things that, while they may not be risky for most women, could be risky for you. Have your other m/c's happened early in pregnancy? If so, it might just be a matter of making it past a certain point in your pregnancy before you can resume your physical activities again. Again, these are all things that your doctor should really know best about.
good luck to you and I hope after all these years of trying that this one is a wonderful healthy pregnancy for you!