Study: Diabetes, Birth Defects Linked

Women diagnosed with diabetes before their pregnancy have
a  higher risk of giving birth to a baby with a birth defect or multiple
defects than a woman who does not have diabetes before giving birth, according
to a new study.

"For single [birth] defects, the risk is three to four times greater,
and about eightfold for multiple defects," says Adolfo Correa, MD, MPH,
PhD, the study's lead author and an epidemiologist at the CDC's National Center
on Birth Defects and Developmental Disabilities.

Women with pregnancy-induced diabetes, called gestational diabetes, were
also more likely to have a child with a birth defect, but generally only if
their weight before getting pregnant was in the overweight or obese range, with
a body mass index (BMI) of 25 or higher.

While the diabetes-birth defects link has been long known, this new research
breaks new ground, says Correa.

"This is the largest study of its kind done on diabetes and birth
defects," he tells WebMD.  The scope was broader than other studies,
too, since the researchers looked at those with diabetes as well as gestational
diabetes. And they looked at nearly 40 defects, both cardiac and
noncardiac.

Even so, another expert cautions that women, even those with diabetes and
planning a pregnancy, should not become frightened by the latest research.
 Ninety-three percent of the birth defects weren't associated with
maternal diabetes. Two percent of the children with single birth defects were
born to mothers who had diabetes before their pregnancy, while 5% of those born
with multiple defects were born to diabetic moms.

Diabetes and Birth Defects

Correa and his colleagues evaluated mothers of more than 13,000 infants with
birth defects and nearly 5,000 infants without birth defects. The children were
born between 1997 and 2003 and were participants in the National Birth Defects
Prevention Study, which drew data from 10 birth-defect surveillance systems in
10 states.

They looked at whether a mother had diabetes, either type 1 or type 2,
before becoming pregnant or whether she developed it during pregnancy. Women
also reported other information, including height and weight, so their BMI
could be calculated. Twenty-four mothers of the nearly 5,000 infants without
birth defects had diabetes before pregnancy; 283 moms of the babies with birth
defects had diabetes before pregnancy.

While diabetes contracted before pregnancy was associated with a wide range
of birth defects, diabetes that came on during pregnancy was associated with a
limited group of birth defects, Correa's team found.

In general, he says, women who got gestational diabetes tended to have
children with birth defects only if their pre-pregnancy BMI had been 25 or
higher.

Among the defects in children born to women with diabetes are heart
problems, brain and spinal defects, oral clefts, kidney and gastrointestinal
tract defects, and limb deficiencies.

Diabetes diagnosed before pregnancy was linked with about 50% of the birth
defect categories analyzed.

Role of High Blood Sugar

Exactly why pre-pregnancy diabetes boosted birth defects risk so much isn't
known. But experts say that high blood sugar (hyperglycemia) plays a role.

For instance, in animal studies cited by the researchers, a mother's high
glucose (blood sugar) has been found to lead to the same in the embryo, causing
biochemical abnormalities that increase oxidative stress and could lead to
incomplete closing of the neural tube, in turn causing such neural tube defects
as spina bifida.

"The new research confirms some early studies," says Janis Biermann,
a spokeswoman for the March of Dimes who reviewed the study for WebMD. But the
research also goes beyond that earlier research, she says, by studying a much
larger group and by going into more detail about a variety of birth
defects.

Women should take the new reseach as a call to take better care of
themselves, Biermann says, to do what they can to reduce the risks.

Women shouldn't think birth defects are inevitable if they have diabetes
before getting pregnant, she says. "Just because there is an increased risk
of a baby having a birth defect if a woman has preconception diabetes doesn't
mean it is going to happen. It just means there is a greater chance than if a
woman doesn't have it."

Women who are already diagnosed with diabetes who hope to get pregnant can
take crucial steps to beat the odds, she says. "It's important to take care
of yourself, exercise, be at an optimal weight, plan your pregnancy, and make
sure the diabetes is well controlled before you get pregnant."

Once you are pregnant, she tells women with diabetes, follow the same
healthy habits and go for regular prenatal care. Those with diabetes, she says,
also need to keep their regular appointments with their diabetes
specialist.

About 1.85 million U.S. women of childbearing age have diabetes, the March
of Dimes estimates.

The study is published in the American Journal of Obstetrics &
Gynecology.

By Kathleen Doheny
Reviewed by Louise Chang
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