Baby got a flat head?

When it comes to infants' risk of developing a flat spot on the head, environment appears more important than genes, a new study finds.

The study, published in the journal Paediatrics, looked at more than 20,000 babies treated for deformational plagiocephaly - misshapen areas in the skull that most commonly manifest as a flattening at the back of the head.

Factors both before and after birth contribute to plagiocephaly. Crowding in the womb is a risk factor, for instance, with the problem being more common in twins and other multiples.

After birth, repetitive pressure on one area of an infant's head - from repeatedly sleeping in the same position, or spending too much time in swings or "bouncy seats" - can lead to plagiocephaly.

However, researchers have also questioned whether genetic predisposition might play an important role. Some studies have found that plagiocephaly tends to run in families, but that could reflect either genetic influences or parenting practices.

In the new study, researchers found that "twinning" was associated with a higher risk of plagiocephaly, but there was no evidence of a difference between identical and fraternal twins.

Because identical twins share all of their genes and fraternal twins share only about half, on average, the finding suggests that genetic predisposition does not explain the tendency of plagiocephaly to run in some families.

On the other hand, environmental factors like position in the womb and an infant's sleep position were important. For instance, 15 percent of babies with plagiocephaly had been born in the breech position -- with the feet or buttocks, rather than the head, closest to the birth canal; that compares with roughly 3.5 percent of births in the general population.

Sleep position, meanwhile, was the most important factor in the "lateralization" of the plagiocephaly. That is, babies who usually slept with their heads turned to the right usually developed a flat spot on the right side of the head, while those who favored the left side usually developed plagiocephaly on that side of the head.

"What our work may imply is that if there is a genetic predisposition for (a) variation like deformational plagiocephaly, there is not any one genetic factor, but instead many, and that there may be different factors in different populations of ethnic diversity," senior researcher Dr. Brian C. Verrelli told Reuters Health in an email.

On the other hand, it seems that environmental factors are "very important" in causing plagiocephaly, according to Verrelli, an assistant professor at Arizona State University in Tempe.

And that, the researcher noted, implies that plagiocephaly can not only be avoided, but also that there is a "high probability" that it will be easily treated.

Since pediatricians began recommending that infants be put to sleep on their backs to lower the risk of sudden infant death syndrome (SIDS), studies have noted a rise in plagiocephaly. To counter that, experts generally recommend that infants get plenty of supervised "tummy time" when they are awake, and that parents avoid leaving them in carriers, swings or other seats for a prolonged period.

Plagiocephaly is often treated in a similar manner - tummy time during waking hours and periodically turning the baby's head when he or she is sleeping, for instance. In some cases, infants are outfitted with a helmet that they wear for a few months to help reshape the skull as it grows.

What has been your experience with plagiocephaly?

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