Are certain women more at risk for depression during and after pregnancy?

Yes, but ... If you have had postpartum depression with a previous pregnancy - or at any other time - you may get it again. But there are no known effective preventive measures, despite what some say. Talk to your obg doctor if at any time during or after your pregnancy you feel extremely anxious, irritable, depressed, cry for no reason, or have unreasonable fears for your baby.
Yes. Women with a history of depression are at higher risk of post partum depression. But post partum depression could affect any new mother. Make sure to discuss with your OB or midwife any past history of depression. Post partum depression is serious. There is help available and no woman should suffer alone.