Persistent Spotting in Early Pregnancy: Causes & What to Expect

Question
my wife is nearly 40 and recently had a miscarriage. we do have a beautiful 2 yr old boy in which she had a trouble free pregnancy. now she is pregnant again and has been spotting almost since the beginning (she is now 12 weeks). we are thankful to have made it to the end of the first trimester but the spotting has been light/dk brown almost everyday. we have had 3 sonograms and they all have been good (baby measures out with 160s heartbeat).  she is having all of the normal symptoms (breast tenderness, cravings, showing, tiredness, gas) my question is now that we have made it to the end of the first trimester does the spotting take on a different meaning? i.e. not implantation or infection. can this spotting affect the growth of the baby long term? she did have one episode of fresh, red bleeding which lasted one day, but we visited the ER and everything checked out (good sonogram). they said it may have been a clot. we're still on pins and needles a bit. thanks for your help.

Answer
Often, at 12 weeks gestation, you can have a "subchorionic bleed" which is a sequestration of blood in the folds of the developing placenta. Usually it does not cause any problems to the pregnancy. As lohg as it is not heavy bleeding with cramps, you should not worry.