Sharing a Womb Can Flatten Skull
Risk greater for twin on the bottom
MONDAY, Jan. 7, 2002 (HealthDayNews) -- Twins who ride out gestation on the bottom of the uterus are far more likely than their womb-mates to suffer a flattening of the skull and neck, a new study says.
The findings takes at least some of the onus off back sleeping for the recent dramatic rise in this defect, known as plagiocephaly, which is almost always treatable.
Experts say the report, from researchers in Iowa and Arizona, is especially significant because as couples increasingly use fertility therapies to conceive, the number of multiple births in this country has surged. Almost half the parents in the latest study had used assisted reproduction, the researchers say.
Although the "Back-to-Sleep" campaign to prevent sudden infant death syndrome (SIDS) has dramatically reduced baby deaths, it has also been linked to flattened infant heads.
"Everyone's blaming back sleeping, but some of these problems may, in fact, have an in utero beginning that is made worse by back sleeping," says Timothy Littlefield, lead author of the study, which appears in the January issue of Pediatrics.
In fact, the theory that womb crowding might deform a developing fetus's skull and neck was proposed more than two decades before the "Back-To-Sleep" campaign began in 1992, says Littlefield, director of research at Cranial Technologies, in Tempe, Ariz. The company makes products to correct plagiocephaly, and is involved in treatment of the condition nationwide.
Mildly flattened heads can return to normal with early interventions, including things as simple as physical therapy and putting affected infants on their stomach while they're awake. More severe cases may require corrective headgear or surgery.
"Other than the aesthetics, there really has not turned out to be any brain injury" from plagiocephaly, says Dr. Steven R. Cohen, a craniofacial surgeon in San Diego.
Experts say there's no good estimate for the prevalence of plagiocephaly.
In an earlier study, Littlefield and his colleagues showed the condition is more common among children born in multiple pregnancies than it is among singletons. Littlefield's group next sought to learn if not only crowding in the womb, but who's getting crowded, affects skull and neck shape.
The researchers studied 140 pairs of twins, about 82 percent of whom were fraternal. In 94 cases, both twins were afflicted with plagiocephaly; in 46 pairs, only one sibling had the condition.
Bottom twins were significantly more likely than their siblings to be afflicted with the condition, the researchers say, and the increased risk held even when both infants were deformed. Those with plagiocephaly were also more likely to have neck troubles, including tightness or a thick-muscled deformation called torticollis.
Surprisingly, says Littlefield, while boys have generally been considered to be at twice the risk of plagiocephaly as are girls, gender didn't seem to play a role in their study.
The researchers say they're not sure why womb position so greatly impacts skull structure. But they suggest the weight of the upper child forces the lower sibling's head against the disfiguring shape of the mother's pelvis, especially when the bottom baby's skull is pointed south.
Exacerbating matters, many infants now spend a lot of time in car seats, carriers, kiddie swings and other apparatus when their skull bones are still malleable, the researchers say.
"Kids are held less and moved around less," says Kevin Kelly, a University of Iowa researcher and a co-author of the study.
What To Do
Parents shouldn't see the findings as a reason not to put their children to sleep on their back, because the risk of SIDS is far more serious than the cosmetic damage of plagiocephaly. Moreover, Kelly adds, "everyone that sleeps on their back isn't necessarily going to develop" the distortion.
Dr. Joseph Shin, director of the craniofacial center at the Yale University School of Medicine, says the most important thing parents can do is pay attention to the shape of their new baby's head. "If it starts out round and gets more asymmetrical, they should be concerned. And if it starts out asymmetrical and stays that way, they should be concerned," he says.
To find out more about the condition, visit the Plagiocephaly Information Web .