Babies who start standing later than other infants might have more challenges with cognitive or adaptive skills by the time they're in preschool than their peers who stand sooner, a U.S. study suggests.

Most babies will start to pull themselves up to a standing position by around nine months of age and be able to stand without support by around 12 months, according to the U.S. Centers for Disease Control and Prevention (CDC).

Overall, the roughly 600 infants in the study stood up with assistance by around 8.9 months on average.

Babies who didn't pull themselves into a standing position until 11 months, however, had significantly lower cognitive and adaptive skill scores on tests done at age four, the study found.

"While we see these associations, these differences do not necessarily mean that the child is impaired in any way," said senior study author Edwina Yeung of the National Institute of Child Health and Human Development.

"There have been very few previous studies looking into this question even though it's so important to understand these very early steps of development," Yeung added by email. "Among studies which have examined the connection, they have shown that earlier timing of gross motor milestone achievement is associated with better memory and processing speed later in childhood."

More on this...

For the current study, researchers focused on standing and other gross motor skill milestones from four to 24 months in children without any diagnosed developmental delays.

The mothers in the study were about 32 years old on average. Most of them were married, had private health insurance, and either a college or graduate school degree. About 45 percent of the women had infertility treatments.

The infants were born at 38 weeks gestational age on average, about one week shy of when they would be considered full term.

Roughly 52 percent of the babies in the study were singletons, 43 percent were twins and 4 percent were triplets.

The connection between later standing and cognitive skills at age four was only statistically meaningful for the singleton babies.

For the twins, the difference in test scores at age four wasn't big enough to rule out the possibility that it was due to chance.

One limitation of the study is that a large number of women didn't show up at clinic visits needed for their children to be assessed, the authors note in the journal Pediatrics. Mothers who skipped clinic visits were generally younger, less educated and less likely to have private health insurance.

Parents should interpret the study results cautiously, in part because of issues with the study population, said Eliza Nelson, a researcher at Florida International University who wasn't involved in the study.

"We have known for a long time that there is no one size fits all pattern of motor development," Nelson said by email.

Children will not necessarily develop more quickly or be smarter if they achieve motor milestones at younger ages, noted Jana Iverson, a psychology researcher at the University of Pittsburgh who wasn't involved in the study.

However, walking can influence language development because babies can become more likely to start communicating about far away objects and bringing objects to caregivers, Iverson said by email. Sitting and crawling also change how babies perceive the world around them.

Parents can use these motor skill milestones as an opportunity to help children with language development and cognitive skills.

"For example, if an infant crawls over to something on the other side of the room, talk to her about it, or if an infant stands up while holding a toy and makes eye contact, comment on the toy and what the infant is doing," Iverson said.

"These types of rich responses have been demonstrated time and again to influence infants' cognitive and language development in positive ways," Iverson added.