Antenatal depression can be caused by:

a hormone imbalance during pregnancy 

in addition to this you may also experience antenatal anxiety, for instance: anxieties around parenthood (after all this is a life changing event)

pregnancy sickness and tiredness (accepting the physical changes happening to your body)

concerns how this will impact on your relationship ( how does your partner or family feel about the baby?)

economic worries ( what is the cost, can we afford this?)

difficulties with previous pregnancies

Postnatal depression should not be confused with 'baby blues', the majority of women experience mood swings during the first few days after having a baby and are often tearful. The 'baby blues' do not last more than two weeks after giving birth, if these symptons do not disappear, it may be that you are developing postnatal depression. At least one in ten women suffer from postnatal depression which is a clinical depression, research also suggests that one in twenty five new fathers are affected, often at the beginning men can feel 'left out' and find it difficult afterwards to adjust into all the lifestyle changes associated with fatherhood

Perinatal OCD is an under-recognised difficulty that new mothers can experience. Cases of Perinatal OCD are similar to OCD with the experience of intrusive thoughts but can be focused on the baby. This can lead to/ pair with complusive behaviour than can focus on ensuring baby's health and safety 

Postpartum psychosis is a rare but serious mental health illness and should be treated as a medical emergency that can affect a woman soon after having a baby. If not treated immediately, you can get rapidly worse and could neglect or harm your baby or yourself. See a GP immediately if you think you or someone you know may have developed symptoms of postpartum psychosis. Symptoms can include: hallucinations, delusions, a manic mood, loss of inhibitions, feeling suspicious or fearful, restlessness, feeling very confused or behaving in a way that's out of character