NEW YORK, Nov 19 (Reuters Health) -- A low weight at birth has been linked
to high blood pressure in childhood and adulthood, but figuring out the
explanation for the connection has been difficult, researchers report.
Now, the results of two studies suggest that an improperly functioning
placenta -- the structure within the uterus that passes nutrients from mother to
fetus -- may interfere with fetal development and increase the risk of high
blood pressure. Both studies are published in the November 20th issue of the
British Medical Journal.
According to the author of one of the studies, Dr. Terence Dwyer of the
University of Tasmania in Australia, poor nutrition during pregnancy has been
suspected as a cause of low birth weight. The thinking has been that, besides
reducing birth weight, poor nutrition "programs" a child to develop health
problems like high blood pressure, Dwyer told Reuters Health in an interview.
But, based on a study of 888 children, including 104 twins and triplets,
Dwyer and his colleagues conclude that a poorly functioning placenta is more
likely than the mother's diet to predispose a child to develop high blood
pressure later in life.
Based on the children's blood pressure readings and weight at birth and at
age 8 years, the authors confirmed that children with lower birth weights tended
to have higher blood pressure in childhood. This link was stronger in twins and
triplets, who are exposed to the same conditions during pregnancy, than it was
in other children.
The link between low birth weight and high blood pressure was still
present even after the researchers accounted for other factors that could have
affected the results, including breastfeeding, smoking or alcohol use by the
mother, and the mother's education.
The link between birth weight and high blood pressure in twins strongly
suggests that factors besides the mother's lifestyle play at least a partial
role, according to Dwyer. Since twins have the same mother, if one weighs less
at birth, "this can't be solely due to the mother's habits," he pointed out in
the interview.
"Our results, and those of the accompanying paper don't say that maternal
smoking and diet are entirely unimportant," Dwyer cautioned. "What they do say
is that there appears to be something very important happening in the proximity
of the placenta. What that is remains to be determined," he added.
In the second study, researchers led by Dr. Neil Poulter, of the Imperial
College School of Medicine in London, reached a similar conclusion when they
evaluated 479 pairs of female twins.
Based on birth weight, and on weight and blood pressure when the twins
were an average of 54 years old, the researchers found that lighter infants were
more likely to have high blood pressure as adults.
The implication is that "it cannot be different maternal nutrition which
produced the weight differences, and hence blood pressure differences, because
the twins had the same mother," Poulter told Reuters Health. "It suggests that
what reached the fetus is different, and so you tend to blame the placenta," he
noted.
