There's no one clear cause for depression after childbirth. It's likely that physical, emotional and lifestyle factors all play a role.

Physical changes
After childbirth, your body goes through a number of physical changes that may lead to depression. Immediately after you give birth, your hormone levels fluctuate. For example, the levels of estrogen and progesterone — which greatly increase during pregnancy — drop dramatically. This abrupt change may trigger depression, just as smaller hormonal changes can lead to mood swings and tension before your menstrual period.

The hormones produced by your thyroid gland also may drop sharply. This gland, located at the base of your neck, helps regulate your metabolism — how your body uses and stores energy from the foods you eat. If your thyroid isn't producing enough hormones, you may feel tired, sluggish and depressed.

In addition to hormone level shifts, the amount of blood in your body, your blood pressure, your immune system and your metabolism all change after you give birth. These changes can affect how you feel physically and emotionally, causing fatigue or mood swings.

Emotional factors
If you're sleep-deprived and overwhelmed with the task of caring for a newborn, minor problems can seem much greater. Difficulty coping with things that were easily managed before delivery may lead to frustration and depression. Other emotional influences that may contribute to depression include:

• A sense of lost identity — who you were before your baby was born

• An unsatisfying birth experience, such as having your spouse called away or having medical complications that make it difficult to care for your baby

• Anxiety, doubts or unrealistic expectations about being the perfect mother or having the perfect baby

• Feeling less attractive

• Feeling less in control over your life

Lifestyle influences
Factors in your lifestyle also may lead to depression. For example:

• A baby with a high level of needs

• Exhaustion from caring for a new baby or multiple children

• Financial problems

• Lack of support from partner, family or friends

• Postpartum pain or delivery complications

• Problems with breast-feeding

• Relationship difficulties

Postpartum depression affects women of all ages and races. It can develop after the birth of any child, not just your first. If you experience depression after one childbirth, however, your chances of experiencing depression after a subsequent pregnancy are between 50 percent and 100 percent. A personal history of depression also increases your risk.