Researchers Find Useful Method to Determine Birth Weight of Babies Born to Obese Women

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Title: Researchers Find Useful Method to Determine Birth Weight of Babies Born to Obese Women
URL: http://www.pslgroup.com/dg/22559A.htm
Doctor's Guide
July 9, 2008

HOBOKEN, NJ -- July 9, 2008 -- Researchers have found what they believe to be the most accurate way of predicting the birth weight of babies born to the growing number of obese mothers, according to a study published in Ultrasound in Obstetrics and Gynecology.

Researchers from the University of Rochester Strong Memorial Hospital, Rochester, New York, have recorded accurate results in more than 9 out of 10 cases using the gestation-adjusted projection method (GAP).

The GAP method uses a range of ultrasound measurements, taken when the mother is 34 to 36 weeks pregnant, and a mathematical formula to determine whether the baby is larger than the average size of babies for its gestational age. This data is then used to predict the final birth weight.

"Obesity is a risk factor for almost all obstetric complications. It is particularly important to identify high birth-weight babies over 4,000 grams as these are associated with higher complication rates for mothers and babies," said Loralei Thornburg, MD, Division of Maternal Fetal Medicine, University of Rochester Strong Memorial Hospital.

"Because a simple visual ultrasound is less accurate in obese women, we need to use any measurements that we can glean from the ultrasound to predict the birth weight."

Dr. Thornburg and colleagues looked at 357 pregnant women who were obese, according to their self-reported weight before pregnancy, and 1,025 who were of normal weight. All were carrying a single baby and their average age was 27.

The obese women were divided into 3 groups: (1) 45% of women with a body mass index (BMI) of between 30 and 34.9; (2) 29% of women with a BMI of between 35 and 40; and (3) 26% of women who were morbidly obese, with BMIs ranging from 40 to 58. Of all the women, 17% had a BMI of more than 50.

Researchers used the GAP method to compare the estimated birth weight, based on scans taken between weeks 34 and 36 of the woman's pregnancy with the baby's weight on delivery. The data was then collated for the normal weight control group and the 3 obese groups.

The GAP method was able to predict the birth weight within 20% in 93% to 95% of cases in the first group, within 15% in 82% to 86% of cases in the second group, and within 10% in 59% to 70% of cases in the third group.

Overall, accuracy levels between the normal weight control group and the obese patients were very similar in most cases. However, the authors note that the largest errors between predicted and actual birth weight occurred in women in the most obese group. The researchers were also able to rule out the risk of a high birth-weight baby in over 80% of cases, regardless of the mother's BMI.

There was also a clear link between the mother's BMI and the final birth weight of her baby. Mothers who were morbidly obese tended to produce babies that were, on average, more than 400 grams heavier than the women who were normal weight.

"In our view, GAP may represent the best method for predicting the birth weight of babies born to obese mothers. It has high levels of accuracy and provides a convenient and easy-to-use method for medical staff," said Dr. Thornburg.

"Obesity and high-weight babies pose extra risks for pregnant women and present real and growing challenges for health professionals. Being able to identify those risks more clearly is an important step in the management of obese pregnant women and their babies."

SOURCE: Wiley-Blackwell

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