April 12, 2012
A new Canadian study has shed fresh light on a growing problem in the
nation’s maternity wards: pregnant women whose obesity poses health
risks for the fetus that may be as dire as the effects of smoking or
The swelling ranks of obese, expectant mothers are at heightened
danger of having miscarriages, still-births and premature babies, and
more likely to deliver children who develop diabetes, cardiovascular
disease and even spina bifida. A study released just this week found
obese women were almost 70% more likely than others to have an autistic
The reasons for such complications have not been clear, but the
just-published Canadian research on rats fed a special high-fat diet
concludes that obesity undermines development of blood vessels in the
placenta, which in turn deprives the fetus of enough crucial oxygen. The
findings point to the fundamental impact that being overweight has on
giving birth, but could also help develop drugs to improve results for
obese mothers, the authors say.
“These babies, they now have been programmed in utero,” said Dr.
Andrée Gruslin, a maternal-fetal medicine specialist at the University
of Ottawa. “Unless something drastic changes, these babies are going to
grow to be obese individuals, and they’re going to have hypertension,
diabetes, cardiac problems … And then it’s a vicious circle, because
then they’re going to get pregnant and so on and so forth. It’s a real
The team behind the research cautions that the study used animal
subjects, meaning there is no guarantee the findings would translate
directly to humans. They note, however, that the female rat models
closely parallel women in the early stages of pregnancy, and the study
confirms earlier suspicions about what makes obese pregnancy so risky.
“I think it’s a very important study,” said Dr. Gideon Koren, head of
the respected Motherrisk program at Toronto’s Sick Kids Hospital, and
not involved in the study. “It fits the human experience and, actually,
it should serve as a red flag for all of us. This is preventable, we
know what causes it, but we don’t do enough about it.”
Studies suggest up to 23% of pregnant women are clinically obese,
accounting for as many as a quarter of the 300,000 births in Canada
annually — while actually changing the face of obstetrics clinics.
“Most clinics now in North America have to be equipped with special
beds, special chairs, special examination tables, because it’s not
infrequent to see a woman with a BMI of 50 or higher,” said Dr. Gruslin.
And research indicates they bring a host of complications to the
birth process. Those include higher risk of miscarriage and stillbirth,
as well as having a baby born premature, too small or too large. The
children are also more apt to suffer from cardiovascular disease and
type-2 diabetes later in life, said Sandeep Raha, a McMaster University
biochemist and lead author of the study.
The mother’s obesity also appears to boost by two to three fold the
possibility of the child being born with spina bifida, said Dr. Koren.
Although the specific outcomes are different, the mother-weight
factor is likely as significant a risk as pregnant women drinking —
which can trigger fetal-alcohol syndrome — or smoking, which boosts the
risks of conditions such as cleft palate and crib death, said Dr.
Gruslin. The percentage of obese mothers — not even including those
merely overweight — exceeds the 13% to 15% of women who smoke while
expecting, noted Dr. Koren.
It is difficult to examine why motherhood obesity can be dangerous,
because of concerns about harming the fetus through research
interventions. Animals used in previous studies were made obese with
extra feeding shortly before pregnancy, unlike the many obese pregnant
women who have had weight problems most of their lives.
For the study, published this month in the journal PloS ONE, Prof.
Raha and colleagues used rats that were fed a high-fat diet from birth,
mimicking as much as possible the condition of the human mothers.
The high-fat rats were more than four times as likely to have
stillborn pups and three times as prone to miscarry as a control group
fed a healthier diet, while they had fewer pups per litter, and
offspring that weighed less on average.
Testing showed that the blood vessels in the obese rats were less
“mature,” meaning more likely to have problems like leaking and poor
nutrient delivery, and indicated there was less oxygen pumped into their
“That means the fetus is potentially getting less oxygen, which could be a huge problem,” said Prof. Raha.