Babies with certain birth defects are much more likely to be abused as infants and toddlers than other young children, a U.S. study suggests.

Babies with malformations of the mouth and jaw known as cleft lip and palate were 40 percent more likely to be abused by their second birthday than those born without birth defects, the analysis of about 3 million children in Texas found.

For infants born with spina bifida, a spinal cord disorder linked to lower limb paralysis and cognitive delays, the odds of maltreatment were 58 percent higher, researchers reported in the journal Pediatrics.

Down syndrome, a chromosomal defect tied to physical abnormalities and intellectual impairment, didn't appear to make abuse any more likely by age two than it would be for babies born without birth defects, the study also found.

"Understanding the factors that place children at an increased risk for maltreatment is crucial for prevention," said study leader Bethanie Van Horne, assistant director for state initiatives for the Children's Learning Institute at the University of Texas Health Science Center at Houston.

"Parenting is challenging - even for typically developing children in well-resourced homes," Van Horne added by email. "The medical complications of birth defects like spina bifida or cleft lip or cleft palate add another level of stress and complexity to infant care."

To explore the connection between birth defects and maltreatment, Van Horne and colleagues reviewed data from a registry of birth defects for children born in Texas from 2002 to 2009 as well as state records on reported abuse.

The vast majority of children in the study were born without birth defects. About 3,700 had Down syndrome, while roughly 2,900 had cleft lip or palate and almost 1,000 had spina bifida.

Overall, about 67,000 of these children had a substantiated case of maltreatment by their second birthday, a prevalence of 23 cases for each 1,000 kids.

For Down syndrome, the prevalence was similar, with 20 cases of abuse for each 1,000 children.

The prevalence of abuse was higher - 36 per 1,000 - with cleft lip and palate and higher still - 38 per 1,000 - with spina bifida.

It's possible that fewer infants and toddlers with Down syndrome experienced abuse by age two in the study because these infants initially look and act very similar to babies without birth defects, Van Horne said.

Among the maltreated children, the infants with cleft lip and palate or spina bifida were about two to three times more likely to experience abuse in their first month of life.

The most common type of abuse was neglect or lack of supervision, followed by physical abuse, physical neglect or medical neglect, the study found.

One shortcoming of the study is that abuse noted for certain families in the study might not have always involved the specific infant included in the study and might have instead been related to another child in the household, the authors acknowledge. Abuse cases reported outside of Texas were also not part of the study, which might have contributed to an underestimate of maltreatment.

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Even so, the findings suggest that when babies have visible birth defects that impact interactions with them, parents may need extra support from clinicians to come to terms with anger, grief or other feelings that can surface when babies have abnormalities, said Dr. Bruno Grollemund, a specialist in orthodontics and member of the Strasbourg cleft competence center in France.

"This is particularly important for midwives and pediatric nurses who are the medical staff in whom parents confide most readily," Grollemund, who wasn't involved in the study, said by email. "If full use is made of these teams and careful attention is paid to the child as a unique being, the parents will feel less isolated, and will be in a better position to reach the decisions that will affect their future."

Children may fare even worse in the developing world, according to Erin Stieber. Stieber works for Smile Train, an international charity devoted to cleft repair surgeries.

"Poorer regions lack the resources and training to treat cleft and to address the special needs associated with it - such as difficulty eating, breathing and speaking - which can lead to social isolation and shame," Stieber, who wasn't involved in the study, said by email. "The challenge is often complicated by a lack of understanding, even negative mythology, about the causes of cleft."