It's no secret that fussy newborns can be especially challenging for parents already facing physical and mental exhaustion from caring for a new baby.

But now science backs up the impact on parents: The less soothable the infant, the more distressed the mother.

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Mothers of highly irritable infants experience greater depressive symptoms, according to new University of Michigan-led research. The nationally representative study, which included data from more than 8,200 children and their parents, appears in Academic Pediatrics.

The study is also believed to be the first to explore whether the degree of a baby's prematurity in combination with infant fussiness may influence the severity of maternal depressive symptoms.

Researchers found that mothers of very preterm, fussy infants (born at 24-31 weeks) had about twice the odds of experiencing mild depressive symptoms compared to moms of very preterm infants without fussiness.

However, mothers of fussy babies born moderate-late preterm (32-36 weeks gestation) as well as mothers of full-term infants were about twice as likely to report moderate to severe depressive symptoms as moms of less irritable babies born at the same gestational age.

"We found that maternal depression risk varied by gestational age and infant fussiness," says senior author Prachi Shah, M.D., a developmental and behavioral pediatrician at U-M C.S. Mott Children's Hospital and an associate research scientist at U-M's Center for Human Growth and Development. "Mothers of fussy infants born late preterm and full term are more likely to experience more severe levels of maternal depression, than mothers of fussy infants who were born more preterm."

"These findings reinforce that all mothers caring for babies with more difficult temperaments may need extra help managing the emotional toll," she adds. "Early screening for infant fussiness may help identify mothers with depressive symptoms in need of support, but may be especially important for mothers of infants born mildly preterm, in whom the symptoms of depression are more severe."

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Shah notes that while very preterm infants have higher morbidity than babies born later, the perinatal care of infants born very preterm may actually help buffer against more severe maternal depression.

Very preterm infants are often cared for in a neonatal ICU setting where part of the specialized care includes guidance and support. As parents transition home they often receive an enhanced level of postnatal support and developmental follow up, including referrals to early intervention programs, home visiting and subsequent care in neonatal clinics.

"The additional support and services provided to families of very premature children help prepare parents for the potential challenges associated with caring for a preterm infant and may help mitigate the risk for maternal depressive symptoms," Shah says.

However, she notes that mild depressive symptoms may progress into more severe depressive symptoms and should also be addressed as early as possible.

Additionally, researchers found that maternal characteristics associated with prenatal stress and socioeconomic disadvantages – such as lower income, unmarried status and smoking –were associated with greater odds of both mild and moderate to severe maternal depressive symptoms.

Asian and black race were also associated with greater odds of moderate to severe depressive symptoms, but Hispanic ethnicity was associated with lower odds of maternal depression. Authors say this raises questions regarding the role of culture as a potential risk or protective factor in the development of maternal depression.

The study included data from the Early Childhood Longitudinal Study, Birth Cohort.  Maternal depressive symptoms were assessed through self-reported questionnaires at the baby's nine-month visit.

The study adds to previous research suggesting that mothers of more irritable infants report significantly less confidence and more stress than mothers of less fussy infants. 

"Pediatricians and providers should pay close attention to mothers who describe difficulty soothing their babies," Shah says. "Early interventions may help reduce the risk of maternal depression that negatively impacts a child-parent relationship and that may be harmful to both the health of a mother and child."