A survey last year in the U.S., which has no parental leave policies, found 68% of respondents believed mothers’ mental health would be better if fathers were allowed at least two weeks of paternity leave. Now, that belief has factual backing from an analysis of the effects of Sweden’s 2012 parental leave reforms, conducted by Stanford University economists.

The conclusion? Paternity leave, especially flexible paternity leave, is essential to mothers’ postpartum good health.

Prior to 2012, Sweden ensured 16 months of paid leave per child, of which either parent could avail, but not simultaneously (with the exception of the 10 days immediately after birth). Following reforms that year, the policy was updated to allow both parents to use up to 30 days of that leave ad hoc and simultaneously during the child’s first year of life. “Importantly, these ‘Double Days’ could be taken intermittently; thus, fathers were effectively granted more flexibility to choose, on a day-to-day basis, whether to claim paid leave to stay home together with the mother and child,” the researchers write.

The effects of this policy on women’s mental and physical health are startling: a 26% drop in anti-anxiety prescriptions for mothers in the first six months after birth, a 14% drop in new mothers who required hospitalization or a specialist consultation; and an 11% drop in antibiotic prescriptions among new mothers.

India currently mandates six months of paid maternity leave and encourages flexible return-to-work options for new mothers. However,there is no national mandate for paternity leave and zero encouragement for new fathers to seek parental leave or flexible work arrangements: In 2016, Women and Child Development Minister Maneka Gandhi said of paternity leave, “it will be just a holiday; he won’t do anything.”

Related on The Swaddle:

Zomato First Company in India to Roll Out Gender‑Equal, 26‑Week Parental Leave

“A lot of focus has been on what we can do in the hospital immediately following childbirth, but less on mothers’ home environment, which is where the vast majority of women spend most of their postpartum time. What we’re saying is one important component of that home environment is the presence of the father or another adult caretaker,” Maya Rossin-Slater, one of the research paper’s authors, told the New York Times. Rossin-Slater, along with Petra Persson, examined data from parents who had their first baby between 2008 and 2012, especially the last three months in 2011 before the reforms took effect, comparing it to data in the first three months of 2012, after fathers were allowed flexible, overlapping leave.

The reforms were aimed at promoting father-baby bonding and gender equality (maternity leave, and parenthood in general, disrupts women’s careers and sets them on the path for a lifetime of lower earnings), but had the additional effect of improving maternal health during a period most medical professionals acknowledge as the ‘fourth trimester,’ when women’s bodies are vulnerable due to ongoing physical and biological changes and sleep deprivation, according to the New York Times. The researchers’ analysis showed the average father only availed of these extra days a couple of times, suggesting flexibility was the policy’s most effective factor, enabling families to have two parents present when they needed it most. “The fathers’ presence could have averted the need for more serious medical care, such as by enabling mothers to sleep, seek preventative care or get antibiotics early in an infection, [researchers] said,” Claire Cain Miller wrote for the New York Times.