First-time mothers, women under the age of 25, and women who have given birth to twins are all at an increased risk of complications.

First-time mothers, mothers under the age of 25, and mothers of twins have the highest risk of postpartum depression, according to a survey of more than 1.1 million moms around the world.

Researchers from the University of Virginia School of Medicine, Johns Hopkins University, and Flo Health found that mothers with twins who are over 40 are most at risk.

With a sample size of over a million new moms, the findings of this study are both significant and definitive. There are few large-scale studies of postpartum depression. Postpartum depression is a common but often misunderstood psychiatric disorder that affects women across the globe, according to the study’s senior author and director of the Reproductive Psychiatry Research Program at the UVA School of Medicine, Jennifer Payne, MD.

For both mothers and their children’s sake, the researchers say, it is critical to better understand the risk factors for postpartum depression. Women are twice as likely as men to suffer from depression during childbirth, according to researchers. After the birth of a child, women are more likely to suffer from major depression.

Researchers have found that the risk of major depression and other psychiatric disorders in the children of mothers who suffer from postpartum depression is higher. Having a mother who suffers from postpartum depression is also linked to a lower IQ and a slower language development in children, as well.

As the researchers write, “there is an increasing necessity to identify risk factors that place women at elevated risk, prior to the onset of affective illness,” during this vulnerable time period, in order to implement preventive measures.

For the study, researchers looked at responses from more than 1.1 million new mothers to Flo’s “After Childbirth Survey,” an app that helps women track their period and menstrual cycles.

At 10%, women in the 18-to-24-year-old age range were most likely to report symptoms of postpartum depression. Finally, the rate of postpartum depression dropped to 6.5 percent among women aged 35-39, before rising slightly among women aged 40 and older. When compared to first-time moms, women with previous pregnancies had lower rates of postpartum depression across all age groups.

Postpartum depression was more common in mothers of twins than in mothers of a single child, with 11.3% of twin moms reporting symptoms compared to 8.3% of single moms. Mothers who had twins were more likely to suffer from postpartum depression than those who had a single child, according to a study published in the journal Pediatrics. Having twins puts women over the age of 40 at “markedly high risk” for postpartum depression, according to the researchers.

Postpartum depression rates among mothers of both sexes were not significantly different, according to the study.

The vast majority of women who suffer from postpartum depression are not diagnosed or treated. Postpartum depression can be diagnosed and treated earlier if new mothers are aware of risk factors such as age, first pregnancy, and twin pregnancies, according to Payne. Both mothers and their children benefit from early intervention in postpartum depression. “