Anterior placentas are extremely common and generally do not cause complications. The exception is if you have had a prior c/section. Then, in some cases, the anterior placenta can attach itself to the old scar in the uterine muscle, a situation called placenta accreta (or percreta or increta, depending if the placenta goes deeper into the muscle, or even through the entire uterus, respectively). This can cause hemorrhage with delivery, necessitating blood transfusion or even hysterectomy. Fortunately, if you have never had a c/section, this is quite rare.
ACK!!! Just how I needed to start off my day!!!