The four-metre cloth sash (also called iwata-obi), usually obtained from a shrine or Buddhist temple with a reputation for help with childbirth, and traditionally worn around the waist by pregnant women (today about 90%). It is worn from the fifth month of pregnancy starting from the day of the dog, who is associated with easy delivery. Often the doctor will inscribe the character for 'happiness' on the sash.
A Popular Dictionary of Shinto. Brian Bocking.