Postpartum depression is a medical illness related to pregnancy and childbirth that can be treated, and it's more common than you might think. It affects about 11% of women after giving birth. It can develop anywhere from a few weeks to a year after delivery, but it's most common in the first three months postpartum.

A new study reported by HealthDay News suggests that women whose final stages of pregnancy occur during the short, dark days of winter may be at increased risk for postpartum depression. It has to do with reduced exposure to sunlight -- the same cause that contributes to seasonal affective disorder, or SAD. That's a type of depression that usually starts in fall and winter and disappears in spring and summer.

Common symptoms of postpartum depression include:

• Feelings sad, anxious, hopelessness, pessimism, guilty, worthlessness, helplessness, or "empty" mood for more than a couple of weeks.
• Frequent ups and downs
• Loss of interest or pleasure in hobbies and activities that you once enjoyed,  including sex
• Fatigue
• Difficulty in concentrating, remembering, or making decisions
• Lack of sleep or oversleeping
• Suicide attempts
• Irritability
• Loss of weight and/or appetite, or overeating and weight gain.

Cause of postpartum depression

No one knows why some women get postpartum depression and others don't. The sharp drop in the hormones estrogen and progesterone after childbirth may trigger the illness, and lack of sleep is one of the major factor as well. Some women face self-identity complex and feel new responsibilities entering motherhood, and this can contribute in.

If you've had depression in the past, a family history of depression or mental illness, a traumatic life event during pregnancy, alcohol or drug abuse, trouble during childbirth or issues with the baby’s health, mixed feelings about the pregnancy, and no strong support system, you're more likely to develop postpartum depression.

Note: If you're breastfeeding, it's crucial to know that antidepressants can be passed to your infant through your breast milk. Though this is shown to be safe for many drugs, it's best to consult your doctor if you have safety concerns. Postpartum depression itself poses risk to an infant, if a mom goes without needed treatment.