Single artery umbilical

I went to the doctor yesterday for the anatomy scan (18w2d). Everything was great except I was told that I only have one artery, instead of two, in my umbilical cord. The doctor said that this normally doesn't cause any problems, I will just have to have more ultrasounds to ensure that our baby girl is growing at a normal rate. Has anyone else been told this? Just slightly concerned and overwhelmed. I mean, it doesn't take much!