Anorectal malformations are birth defects in which the anus and rectum fail to form correctly, usually during the fifth to seventh week of pregnancy. In some cases, there may be a membrane that covers the anal opening, while in others, the anal passage is too small or located too far forward. In other cases, the rectum and anus are not properly connected to each other. About half of the time, a baby born with an anorectal malformation will have some other abnormality as well such as a congenital heart defect, tethered spinal cord, limb defect, Down syndrome, Hirschprung disease or an abnormally formed kidney and/or urinary tract. Depending on the specific malformation, an anorectal abnormality can be repaired via surgery.