Disclaimer: I am a doctor, but not an obsterician and this is personal advice, based on my own research and experience, not professional advice
LeBFG, I'm 27 weeks and have a bicornuate uterus (it's shaped a bit like a Y or a mickey mouse face but all one cavity on the inside). The terminology used can be a bit confusing and different terms are also used interchanably sometimes.
Basically, the internal reporductive organs form from two ducts in the embryo. At various points in development the ducts can fail to fuse which can result in anything from a slightly abnormal shaped uterus to two a whole duplicate systems - two uteruses, two cervicies and even occasionally two vaginas - and everything in between.
Arcuate refers to a uterus that is abnormaly shaped on the outside, but a single cavity inside. Mine can also be described as arcuate (which is what I mean by confusing terminology)
In some cases, depending on the extent of the abnormality, arcuate can put you at higher risk of breech presentation and pre-term labour, but doesn't carry other risks. It can also make it harder to get pregnant, but I would say not in your case since this is your second pregnancy.
As far as I know stories like pebspop's whilst very sad, and I am sorry for your loses, are the exception not the rule.
We had an obstetric appointment last week and were told I'm still considered low risk.
Good Luck.