Adipose Pill Necklace's functioned as a portable Inducer, when turned it activates the Birthing Process of a being with Adipose within. They were given away free with every three week Adipose Pill course.
The Doctor managed to attached two necklaces to an Inducer to cancel out Matron Cofelia's Inducer. To do this two Adipose pill necklace's are needed. The Doctor used his and one stolen by Donna Noble. (DW: Partners in Crime)