Often it is associated with the fear and stress of the pregnancy. Other factors include unintended pregnancy, hyperemesis gravidarum, financial issues, living arrangements and relationships with the father and family. Typically, depression symptoms associated with pregnancy are categorized as postnatal depression, due to the onset of symptoms occurring after childbirth has occurred. The following is a breakdown of when a group of various women began to feel the onset of symptoms associated with depression:

11.8 percent at 18 weeks
13.5 percent at 32 weeks
9.1 percent 8 weeks after the birth
8.1 percent 8 months after the birthIn a recent article posted by The BabyCenter, the authors stated that "For years, experts mistakenly believed that pregnancy hormones protected against depression, leaving women more vulnerable to the illness only after the baby was born and their hormone levels plunged." This is a possible explanation as to why antenatal depression has just recently been identified. Prevalence and causes
The prevalence of antenatal depression differs slightly by region of world. In the United States, antenatal depression is experienced in as many as 16% of pregnant women, while in South Asia it is experienced in as many as 24% of pregnant women. Its becoming more prevalent as more medical studies are being done. Antenatal depression was once thought to simply be the normal stress associated with any pregnancy, and was waved off as a common ailment. It can be caused by many factors, usually though involving aspects of the mothers personal life, such as family, economic standing, relationship status, etc.
In fact, positive antenatal screenings administered in the first or third trimester are found to be high risk factors for early cessation in breastfeeding. Studies also report that the environmental effects of maternal depression affect the developing fetus to such an extent that the impact can be seen during adulthood of the offspring. The effects are worse for women from low socio-economic backgrounds. In a recent study by Coburn et al., maternal prenatal depressive symptoms predicted significantly higher number of infant health concerns at 12-weeks (3 months) of age. The health concerns included rash, colic, cold, fever, cough, diarrhea, ear infections, and vomiting. Additional concerns for women in low-income backgrounds includes low birth rate and preterm births.An interesting and informative area of research has been done to see the role of confounding variables in relationship of maternal prenatal depression with infant health concerns. Age of mother, romantic partner, education, household income, immigrant status, and number of other children, breastfeeding, gestational age, birth weight are some of the mediating or moderating factors which are found correlated with infant health concerns. The studies of post-partum depressive symptoms are relatively more than those of prenatal depression and the studies should look into the role of various factors during pregnancy that may impact the health of infants, even continuing into adulthood. Male Perspective for Antenatal Depression
Fathers can also experience depression during their partners pregnancy, commonly displayed as fatigue or changes in sleep and eating patterns.