Women who give birth in winter or spring may be less likely to experience postnatal depression, finds a new study into the risk factors of developing post-natal depression.
The research, to be presented at the Anesthesiology 2017 annual meeting, also uncovered a number of other factors associated with a lower risk of postnatal depression: a higher gestational age (delivering further along in a pregnancy) and having anaesthesia, such as an epidural, during birth.
"We wanted to find out whether there are certain factors influencing the risk of developing post-partum depression that may be avoided to improve women's health both physically and mentally," said lead author Jie Zhou of Brigham & Women's Hospital in Boston.
To do so, Dr Zhou and his team reviewed the medical records of 20,169 women who gave birth between June 2015 and August 2017. Of these mothers, 817 or around 4 per cent were diagnosed with postnatal depression.
Along with fewer cases of PND recorded in mums of winter and spring babies, the results also demonstrated that women with a higher body mass index were more likely to be diagnosed with depression. Additionally, caucasian women had a lower risk of PND, compared to women of other races.
There was no link between how women gave birth and their likelihood of developing the mental health condition.
While the study didn't set out to understand why certain factors may be associated with postnatal depression, Dr Zhou has a number of theories to explain the results.
"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," he notes. "While women with increased BMI needed more hospital-based maternal outpatient follow-ups and had more pregnancy-related complications, which could affect maternal outlook."
Regarding the protective effect of gestational age, Dr Zhou explains: "It is expected that the mother will do better and be less mentally stressed when delivering a mature, healthy baby."
But why might giving birth in winter and spring be a "protective mechanism" from developing postnatal depression? While the exact reasons remain unclear, the authors note that the finding may be attributed to "the seasonal enjoyment of indoor activities mothers experience with newborns".
The researchers also posit that new mums may receive "better care and more psychological support from other people in harsh weather situations, The Telegraph reports.
While the findings are interesting, research around a seasonal influence on PND is far from definitive. A 2011 Swedish study, published in the American Journal of Obstetrics and Gynecology, found that women who gave birth in the colder autumn and winter months were be more likely to experience PND than those who delivered in spring.
"There's a lot of mixed results out there, which I think indicates we need to know more about what we're trying to figure out," the study's co-author Jennifer Jewell told Reuters Health, noting that the findings may not apply to women in countries closer to the equator with less drastic changes in daylight from season to season.
PND affects around 15 per cent of mothers following the birth of their baby. Women often report feeling tearful, anxious, sad and guilty, without being able to identify an obvious "trigger". Physical symptoms can include a change in appetite, disrupted sleep patterns and difficulty concentrating or "brain fog".
For more information on the signs and symptoms of PND, as well as the available treatments, visit Perinatal Depression and Anxiety Australia (PANDA) http://www.panda.org.au/
If you are suffering from anxiety or depression, or know someone who might be, contact BeyondBlue.org.au (call 1300 224 636), LifeLine (call 13 11 14 or chat online after hours), or PANDA National Helpline (1300 726 306).