Women who give birth in winter or spring are less likely to suffer postnatal depression than at other times of year, a study has shown.

Other factors affecting the risk of postnatal depression, also known as postpartum depression (PPD), included the length of pregnancy, whether or not an epidural was given during delivery, and body mass index.

At least 10% of women experience some degree of anxiety or depression after giving birth. Symptoms include sadness, restlessness, and lack of concentration. PPD typically arises from a combination of hormonal changes, psychological adjustments to motherhood and fatigue, said US researchers.

Dr Jie Zhou, from Brigham & Women’s hospital in Boston, Massachusetts, said: “We wanted to find out whether there are certain factors influencing the risk of developing postpartum depression that may be avoided to improve women’s health, both physically and mentally.”

The team reviewed the medical records of 20,169 women who delivered babies between June 2015 and August 2017. Of the total, 817 (4.1%) suffered from PPD.

Why giving birth in winter or spring should have a positive effect is not known but it could be linked to the “seasonal enjoyment of indoor activities mothers experience with newborns”, said the researchers.

The study also found that a longer pregnancy reduced the risk of PPD, while not having an epidural anaesthetic during delivery increased it. White women were less likely to experience PPD than women of other ethnic backgrounds, the research showed. The mode of delivery had no effect.

The findings were presented at the Anesthesiology 2017 meeting in Boston.