Maternity blues
Maternity blues, also known as baby blues and postpartum blues, is a transient condition that 75-80% of mothers could experience shortly after childbirth with a wide variety of symptoms which generally involve mood lability, tearfulness, and some mild anxiety and depressive symptoms. Baby blues is not postpartum depression, unless it is abnormally severe.After the placenta is delivered, the placental "hormone factory" shuts down causing radical changes in hormone levels, and the woman can suffer symptoms due to withdrawal from the high pregnancy levels of estrogen, progesterone and endorphins. Combined with this shift in hormone levels is the physical, mental and emotional exhaustion - as well as sleep deprivation typical of parenting a newborn. All of these factors contribute to the condition.
Child development
Although there are a large number of studies contemplating the effect of maternal depression and postnatal depression of various areas of infant development, they are yet to come to a consensus regarding the true effects. There are numerous studies indicating impaired development, and equally, there are many proclaiming no effect of depression on development. 
A study of 18-month-olds whose mothers suffered depressive symptoms while they were 6 weeks and/or 6 months old indicated that maternal depression had no effect on the child's cognitive development at 18 months. Furthermore, the study indicates that maternal depression combined with a poor home environment is more likely to have an effect on cognitive development. However, the authors conclude that it may be that short term depression has no effect, where as long term depression could cause more serious problems. A further longitudinal study spanning 7 years again indicate no effect of maternal depression on cognitive development as a whole, however it found a gender difference in that boys are more susceptible to cognitive developmental issues when their mothers suffer depression. 
This thread is continued in a study of children up to 2 years old. The study reveals a significant difference on cognitive development between genders, with girls having a higher score, however this pattern is found regardless of the child's mother's history of depression. Infants with chronically depressed mothers showed significantly lower scores on the motor and mental scales within the Bayley Scales of Infant Development, contrasting with many older studies. A similar effect has been found at 11 years: male children of depressed mothers score an average of 19.4 points lower on an Intelligence Quotient IQ test than those with healthy mothers, although this difference is much lower in girls. 3 month olds with depressed mothers show significantly lower scores on the Griffiths Mental Development Scale, which covers a range of developmental areas including cognitive, motor and social development. It has been suggested that interactions between depressed mothers and their children may affect social and cognitive abilities in later life.
Maternal depression has been shown to influence the mothers’ interaction with her child. When communicating with their child, depressed mothers fail to make changes to their vocal behaviour, and tend use unstructured vocal behaviours. Furthermore, when infants interact with depressed mothers they show signs of stress, such as increased pulse and raised cortisol levels, and make more use of avoidance behaviours, for example looking away, compared to those interacting with healthy mothers. The effect of mother-infant interaction at 2 months has been shown to affect the child's cognitive performance at 5 years. Recent studies have begun to identify that other forms of psychopathology that may or may not be co-morbidly occurring with maternal depression can independently influence infants' and toddlers' subsequent social-emotional development through effects on regulatory processes within the child-parent attachment. Maternal interpersonal violence-related post-traumatic stress disorder (PTSD), for example, has been associated with subsequent dysregulation of emotion and aggression by ages 4–7 years.