Babies born with low weights are more prone to sickness and
have a higher death rate than babies born with normal weights.
But nobody knows exactly why some babies are born with low
birth weights.

Among industrialized nations, the United States has one of the
highest rates of babies born with low birth weights, said Mary
Alice Smith, an environmental health scientist with the
University of Georgia College of Agricultural and Environmental
Sciences.

Small stats

According to the National Center for Health Statistics, around
4 million babies are born each year in the United States. About
7.6 percent of them are born with low birth weights — less
than 2,500 grams, or about 5.5 pounds.

In Georgia, 8.6 percent of newborns are low-birth-weight
babies. That’s one of the highest rates in the country.

About 65 percent of all infant deaths in the United States can
be attributed to low birth weights, Smith said.

Infectious clues

It’s a problem nobody can explain. But there are clues.

“We know that women who have infections during pregnancy have a
higher risk of delivering babies with lower birth weights,” she
said.

Smith focuses her research on understanding how different
levels of bacteria and the infections they cause in the
mother’s body might affect her baby’s development.

During pregnancy, a woman’s immune system changes so her body
won’t fight or reject the developing baby inside. This makes
her more susceptible to infections.

But in many cases, Smith said, the mother may never know she
had an infection or that the infection threatened her baby.

Campylobacters are microorganisms found in the mouth when a
person has periodontal disease and in foods like poultry
products. Exposure to Campylobacter can cause stillbirths in
cattle and sheep and has been found in stillbirths in humans.
Smith is using mice to investigate how this may occur.

Mice infected with Campylobacter have an increased number of
low birth-weights, she said.

The microorganism was found in the placentas (the organ in
pregnant mammals that feeds the fetus) of mouse fetuses with
low birth weights but not in placentas of normal-weight
fetuses.

“This suggests that the bacteria, or the placenta’s immune
responses to the bacteria, are affecting the growth of the
fetus,” she said.

Menacing microbes

Smith is doing similar research with Salmonella and Listeria.

Healthy adults and children can occasionally become infected
with Listeria but rarely show signs of sickness.

It can be deadly, though, for unborn babies. The Centers for
Disease Control and Prevention estimate that Listeria causes
500 deaths in the United States each year. Of these, more than
100 are stillbirths.

A pregnant woman can be exposed to Listeria and not know it.
And if the pathogen has time to reach her unborn baby, it could
kill it.

Smith hopes her research leads to better ways to detect
infections during pregnancy and to understand what levels of
these pathogens cause problems during pregnancy.

This could, in turn, lead to efficient treatments for
infections and reduce the rate of low birth weights and the
sickness and death associated with it.