AHT is most common among children under the age of 1 year.
Dr. Joanne Klevens, of the National Center for Injury Prevention and Control at the Centers for Disease and Prevention (CDC), and colleagues publish their findings in the journal Injury Prevention.
Abusive head trauma (AHT) is defined as a form of physical child abuse - commonly caused by violent shaking or impact on a blunt object - that leads to brain injury in a child or infant.
According to the CDC, children under the age of 1 year are most at risk of injury from AHT, and the most common trigger for the abuse is inconsolable or prolonged crying.
Almost all infants who are subject to AHT experience long-term health effects, including vision problems, delays in development, physical disabilities and loss of hearing, and at least 1 in 4 babies who experience AHT die as a result.
"AHT prevention has primarily focused on providing parents of newborns with information about infant crying and the dangers of violent infant shaking," note the study authors. "Although such programs initially yielded promising results, subsequent rigorous evaluation efforts failed to show reductions in serious AHT incidence."
What is paid family leave?
In 2002, California passed a bill for paid family leave, which was launched on July 1st, 2004.
The bill entitles employees who qualify for State Disability Insurance to earn a proportion of their pay while they take up to 12 weeks out of work, either due to a serious health condition (including pregnancy), to look after a relative with a serious health condition or to look after a newborn, a newly adopted child or a newly placed foster child.
Only two other states in the US have initiated paid leave policies - Rhode Island and New Jersey - and the length of leave and eligibility criteria varies in each state.
Previous studies have suggested paid family leave can reduce stress and depression for new mothers, as well as improve children's responses to external pressures - all of which are known risk factors for AHT.
For their study, Dr. Klevens and colleagues set out to determine whether paid family leave has any impact on hospital admissions for AHT.
To reach their findings, the team compared the AHT hospital admission rate between 1995-2011 in California with seven states that do not have paid family leave: Arizona, Colorado, Florida, Iowa, Maryland, Massachusetts and Wisconsin.
AHT hospital admissions reduced in California
The researchers identified a fall in AHT hospital admissions among children up to the age of 2 years in California after the paid family leave policy was introduced in 2004, compared with the seven states without such a policy.
- It is estimated that each year in the US, around 30 children per 100,000 under the age of 1 year are injured as a result of AHT
- AHT often occurs when a parent or caregiver becomes frustrated with a child's crying
- Bleeding on the brain or at the back of the eyes are common injuries with AHT.
The California paid leave policy was associated with a reduction of 5.1 AHT hospital admissions per 100,000 children under the age of 1 year and a fall of 2.8 AHT hospital admissions per 100,000 children under the age of 2 years.
The findings remained after accounting for potentially confounding factors, such as the percentage of adults with low educational attainment and the rate of unemployment, the team notes.
Additionally, the researchers found that, while states without a paid family leave policy experienced an increase in AHT hospital admission rates during The Great Recession (2007-2009), such rates remained stable in California.
What is more, the team notes that the reductions in AHT hospital admission rates in California occurred despite uptake of paid family leave being low - only 38% of eligible parents received it in 2014 - suggesting that the effect could be larger if more "at risk" parents were able to take advantage of the policy.
While the authors admit that their findings are purely observational, they say their results demonstrate "positive evidence" of the influence paid family leave may have on rates of AHT.
Last year, Medical News Today reported on a study detailing the development of a new test that could help doctors identify which children may be at risk of death from shaken baby syndrome.