My periods start early and then get heavier at the right time, and I've had two miscarriages. Are these two things related?
It's possible you may have what called an "inadequate corpus luteal phase." There are two phases of the menstrual cycle. The first, called the "proliferative," or "estrogenic" phase, is when the lining of the uterus (womb) proliferates (gets thicker). After you ovulate at midcycle, the area of the ovary from which you ovulated, called the "corpus luteum," makes progesterone, a hormone that makes possible the second half of the cycle—the "secretory," or "progestational" part. In the first half of the cycle, the lining grows and is heaped up, and in the second, the lining is matured by the progesterone to prepare for the implantation of a fertilized egg. If this doesn't happen, the progesterone production from the corpus luteum falls, the lining has no more hormonal support to keep it organized, and it falls apart—what you see as a period.
Now, if the corpus luteum is not a good one, and the production of progesterone is therefore less than adequate, then the lining will become fragile before the time you'd expect a well-timed period. This is your early spotting.
But like the uterine lining, the plot thickens.
Progesterone is necessary to keep the lining of the uterus intact for the pregnancy, and if it's too low, a miscarriage can occur. So yes, an "inadequate corpus luteum" can be responsible for recurrent pregnancy loss. But it's very important to understand that more than likely the progesterone is low because the pregnancy is faulty, rather than the pregnancy being faulty because the progesterone is low. But it's impossible to tell once trouble starts brewing, so most doctors will give a pregnant patient with a low progesterone pills or suppositories that will increase the level of progesterone. If the baby's in trouble because the progesterone is low, this may be pregnancy-saving. But you must be willing to accept that if the progesterone is low because the baby's in trouble (the opposite), then giving a patient progesterone will only delay the inevitable miscarriage.
But in my practice I'd rather take that chance and meet any baby halfway.