It is possible, Dr. Nielsen said, that psychological or socioemotioanal factors may be enough to trigger most of the dreams during pregnancy or the post-partum weeks.
However, other factors to be considered for new mothers are the severe sleep disruption, as well as REM sleep deprivation, they undergo in the postpartum period.
Another contributing factor is the fluctuation in hormones, such as oxytocin(Drug information on oxytocin), prolactin, and vasopressin(Drug information on vasopressin). It is possible that these hormones, or their influence on other processes such as breast sensation during sleep, affect the form, intensity or content of dreams.
Finally, Dr. Nielsen said, various psychopathologic influences may play a part, such as insecure attachment.