Based on my clinical experience, it is safe during pregnancy and breastfeeding.
I usually stop LDN at 37 weeks in case the woman may need any opioid type of pain relief during labour.
If there was zero chance of needing opioids, there is no need to stop LDN.
When she is finished analgesia post-delivery, she can resume LDN.
Typically baby may get 1/10th of the medication when breastfeeding. Physiologically, it is harmless to baby at this amount.
If mum is sleep deprived or stressed LDN will be less effective during periods of stress. It will work better when stress is reduced.