Obesity during pregnancy puts
women at higher risk of a multitude of challenges. But, according to a
new study presented earlier this month at the American
Institute of Ultrasound in Medicine annual convention, fetal growth
restriction, or the poor growth of a baby while in the mother’s womb,
is not one of them. In fact, study authors from the University
of Rochester Medical Center found that the incidence of fetal growth
restriction was lower in obese women when compared to non-obese women.
Researchers, led by senior study author and high-risk pregnancy
Thornburg, M.D., conducted the study because a wealth of data
shows that obese women are at greater risk of fetal death or stillbirth.
Unfortunately, in the majority of cases, doctors don’t know why.
Thornburg’s team wanted to determine if fetal growth restriction –
which increases the likelihood of stillbirth – might play a role. She
says growth restriction may go undiagnosed in obese women because it can
be difficult to get an accurate measure of mom’s belly size, which is
a tool used to gauge the baby’s growth – or lack of growth.
“We wondered if the increased risk of stillbirth could be due to a
high level of undiagnosed growth restriction – the idea being that if
the physician doesn’t know that the baby is too small then they
don’t know that mom and baby need additional monitoring, which is
essential to prevent fetal death,” said Thornburg, an assistant
professor in the Department
of Obstetrics and Gynecology at the Medical Center whose research
focuses on obesity in pregnancy.
The team, including lead study author and Maternal-Fetal Medicine
Fellow Dzhamala Gilmandyar, M.D., found that growth restriction was
significantly lower in obese and diabetic women; it was higher in women
with preeclampsia, or pregnancy-induced high blood pressure, and smokers
– a finding in line with past research. Of the babies that had growth
restriction, they determined how many moms were given an accurate
diagnosis before birth and found that the rate was the same for obese
and non-obese women, suggesting that missed diagnoses are not a major
problem in obese pregnancies.
“Our results defeat the idea that undiagnosed growth restriction is
behind increased rates of fetal death in obese women,” noted Thornburg.
Many obese women also have diabetes, which could influence the risk of
fetal death, but more research is needed to understand whether or not
that is the case.
Though stillbirth, most often defined as death occurring after 20
weeks gestation, is not very common in the general population – it
occurs in around six of every 1,000 births in the U.S., according to the
Centers for Disease Control and Prevention – it is more common in
specific populations, including obese women, African Americans and
While the cause of stillbirths in obese women remains elusive,
Thornburg says “One thing we do know is that we are not just dealing
with obesity in pregnancy anymore. We are seeing a real increase in
extreme obesity, which may represent a different condition altogether,
so we need to look at moderate obesity compared to severe, morbid
Thornburg and Gilmandyar reviewed birth record data from more than
16,000 women who delivered at the Medical Center between 2000 and 2010.
Obesity was defined as having a pre-pregnancy body mass index or BMI of
30 or greater and growth restriction was defined as being below the
tenth percentile of expected birth weight for gestational age. After
taking into account the effects of diabetes, high blood pressure and
tobacco use, growth restriction remained lower in obese women (8.5
percent) compared to non-obese women (nearly 10 percent).
“While our study shows that obesity by itself may not be a risk
factor for growth restriction, it is still important to closely monitor
women who also have high blood pressure or who are smokers, because
these are established risk factors for growth restriction,” said
Gilmandyar, who is completing her second year as a fellow at the Medical
In addition to Gilmandyar and Thornburg, Kristin Knight, M.D.,
Maureen Perdue, M.D., Oluwateniola Brown, Tina Jensen, David Hackney,
M.D., and Eva K. Pressman, M.D., from the Medical Center contributed to
University of Rochester Medical Centre