A mother's risk of developing postpartum depression might be influenced by the season in which she gives birth, a new study suggests, with summer and fall posing the greatest risk.

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Researchers say that women who give birth in winter or spring may be at lower risk of postpartum depression.

Researchers also found that women who deliver their baby without anesthesia may be at greater risk of postpartum depression (PPD), while women who give birth at a later gestational age may have a lower risk of the condition.

Lead study author Dr. Jie Zhou, of Brigham & Women's Hospital in Boston, MA, and colleagues believe that their findings may help women to reduce their risk of PPD, by addressing some of the risk factors identified.

The researchers presented their results at the Anesthesiology annual meeting, which was held in Boston this weekend.

PPD is more than the "baby blues." It is defined as extreme feelings of anxiety, sadness, and tiredness that occur after giving birth. Without treatment, such feelings can seriously impact a mother's emotional and physical health. This may make it difficult for her to bond with or care for her baby. In severe cases, a mother may think about harming herself or her child.

Sadly, PPD is common; around 1 in 9 women in the United States experience the condition after having a baby.

While it is difficult to pinpoint one cause of PPD, known risk factors include stress, a history of depression, preterm delivery, and experiencing pregnancy or birth complications.

The new research helps to shed further light on what might contribute to the development of PPD, which could help women to reduce their risk of the condition.

Delivery in winter, spring may lower PPD risk

Dr. Zhou and team came to their findings by analyzing the medical records of 20,169 women who gave birth between June 2015 and August 2017. Of these women, 817 developed PPD.

The aim of the study was to pinpoint specific factors that might influence the risk of PPD, and the team spotted some interesting trends.

The analysis revealed that the risk of PPD was lower for women who gave birth in spring or winter, compared with those who gave birth in the fall or summer.

The researchers suggest that because of the poorer weather conditions in winter and spring, this may encourage more indoor activities with a newborn, which may be more enjoyable and convenient for mothers.

The study also revealed that women who did not receive an epidural or any other anesthetic during delivery were at greater risk of PPD, which the team speculates may be down to the greater pain they experienced.

Higher BMI may be a risk factor

Women who gave birth at a later gestational age were found to have a reduced risk of PPD, which was not surprising to the team.

"It is expected that the mother will do better and be less mentally stressed when delivering a mature, healthy baby," explains Dr. Zhou. 

Additionally, the researchers found that women with a high body mass index (BMI) were more likely to develop PPD than those with a healthy BMI, while white women had a lower risk of the condition than other races or ethnicities.

"The significant difference in the risk of developing PPD between Caucasian and other populations may be due to differences in socioeconomic status among these ethnicities," says Dr. Zhou. "[...] [W]omen with increased BMI needed more hospital-based maternal outpatient follow-ups and had more pregnancy-related complications, which could affect maternal outlook."

The researchers believe that their study has helped to unravel some of the preventable risk factors for PPD, which may help women reduce their risk of this distressing condition.