Epple et al. (1993) suggests that scent-marking by pregnant females could promote group cohesion so that helpers are present at birth.
anal-scent mark: This is when a common marmoset lightly rubs or drags the ano-genital region along a substrate (Stevenson and Poole, 1976).
sternal scent-marking: This behavior is where a common marmoset rubs the sternal region along a substrate (Stevenson and Poole, 1976).
[Primate Fact Sheets]