Junkfood Science: Another blank missile fired at fat pregnant women

April 04, 2008

Another blank missile fired at fat pregnant women

The story has circulated around the world, reporting that a new study supposedly found “obese” pregnant women have hospital stays 4.1 days longer than “normal” weight women, putting a “financial strain on the healthcare system.”

We have now gone beyond any ability to have reasoned discussions about fat. Anyone can make the most exaggerated claim and no one questions it because “everybody knows” obesity is so deadly.

4.1 days (?!?)

The average hospital stay after delivering a baby is 2 days for vaginal deliveries and 4 days after a cesarean delivery among American women. It would have made the news long before now if suddenly all fat women were really spending a week in the hospital — two to three times longer than other women — after having a baby. But no one even thought to question the claim.

When you learn what the study actually found, you’ll see that we have another data dredge finding an untenable correlation. The only purpose it served was to scare fat women, accuse them of burdening the healthcare system and fuel the war on obesity.

The study

The study, published in the New England Journal of Medicine, was led by Susan Y. Chu, Ph.D, and colleagues at the National Center for Chronic Disease Prevention and Health Promotion at the CDC and Kaiser Permanente*. The primary objective of this study “was to estimate the maternal healthcare services associated with obesity during pregnancy.” More precisely, they were looking for correlations between pre-pregnancy BMIs and length of hospital stays when the women had their babies.

“Length of hospital stay for delivery was our primary measure of use of healthcare services,” they wrote, “the total length of stay was defined as the number of days from admission to discharge, and the post-partum length of stay as the number of days from delivery to discharge.”

Rather than cleanly and simply just examine the hospital records for all deliveries during the study period and note the associations between the mother’s BMIs and hospital stays, they used a complex set of criteria to define the study population. Using the electronic database from Kaiser Permanente Northwest, a large health maintenance organization in western Oregon and Washington state, they identified 19,538 women who had became pregnant from January 1, 2000 through 2004, and had carried their babies at least 20 weeks. They then excluded:

· all pregnancies of mothers who weren’t still Kaiser members at the time of delivery

· all home deliveries

· all pregnancies that they didn’t have in their electronic database the mother’s weight from 6 months before she became pregnant and through the first trimester

· all pregnancies that they didn’t have the mother’s height after the age of 16 years on file

They excluded one-third of the pregnancies (6,096 women). Those they excluded were significantly younger, leaving more older pregnant women in their analysis.

There were also distinct differences between the most “obese” women and the “normal” weight women in this cohort. The largest women were considerably older, 71% more likely to be Black or Hispanic, 227% more likely to be on Medicaid (or Washington State’s Basic Health Program) and of lower socio-economic status, and 64% more likely to have had three or more babies. In other words, weight in this cohort was a marker for these significant confounding factors, which need to be considered before credibly pointing to weight itself.

[Remember, how failing to account for aging, the most single most important risk factor for dying, was one way that disproven original claim of “300,000 deaths attributed to obesity” came about?]

Hospital days were determined by billing records. While not part of their primary outcome measures, they also used billing records to attempt to make correlations between obesity and prenatal screening procedures, but without examining any medical records or validating any clinical condition, these mostly reflect clinical care guidelines for obesity, making any sound conclusions about medical necessity impossible.


Length of hospital stay was examined in several ways, both from admission (which is variable, depending on when the women were urged to come into the hospital, transportation, how far away they lived from the hospital, planned cesarean sections or inductions, etc.) and from delivery to discharge. [All average hospital stays had a standard error of ±0.1 day.]

The total hospital stay for vaginal deliveries averaged 3.2 days among women of “normal” weight and 3.7 days among the most “extremely obese” (BMI ≥40). For cesarean deliveries, it averaged 5.2 days among the “normal” weight and “very obese” (BMI 35-39.9) women, and 5.3 days for the most “extremely obese.”

The hospital stays from delivery to discharge were 1.9 days among women with “normal” BMIs and 2.0 days among the most “extremely obese.” Cesarean deliveries averaged 3.5 and 3.7 days, respectively.

But, remember those confounding factors? After they adjusted for age, multi-parity (number of pregnancies), race, delivery and other conditions, the total hospitals stays averaged 4.4 days for the “normal” weight and “overweight” women ... and 4.5 days for all of the “obese” women, regardless of how fat they were.

0.1 day difference

The difference was within the standard error and not statistically tenable (beyond random chance or a math error). There was actually no difference in hospital stays correlating with weight itself.

0.1 day difference — not 4.1 days, as was heard in the news

That’s about 2 hours. What, we are now blaming fat women for the inefficiency of the discharge process? The authors made no attempt to determine what might explain those 2 hours, even if it had been a tenable correlation, as no discharge procedures were considered (Medicaid paperwork, transportation issues, etc.). It was attributed to the mothers’ weights:

[T]he mean length of hospital stay for delivery was significantly greater among women who were overweight, obese, very obese, and extremely obese than among women with normal BMI... of the 4 million births each year in the United States, approximately 1 million involve obese women. Thus, even a small increase in the cost of health care associated with obesity will have substantial economic implications.

The daily reporting of overstated claims about obesity calls upon all of us to set aside preconceived beliefs and examine the facts, rather than accept the spin without thinking. Women and healthcare professionals who want accurate and impartial reporting of this study’s primary finding may substitute this headline:

Among a sample of pregnancies in Kaiser Permanente’s managed care records, there was no correlation between the women’s obesity and the length of hospital stay.

P.S. As we’ve seen in other studies, there appears to be no correlation between obesity and chances of getting pregnant in this study, either. “Obese” women made up 26% of the pregnant women; 27% of the pregnant women were “overweight” and 45.3% were “normal” weight. In this study, there was also no difference in rates of stillbirths due to obesity. The most “extremely obese” women had the very same stillbirth rate (0.6 percent of pregnancies) as the “normal” weight and “overweight” women.

© 2008 Sandy Szwarc

*In 2002, this bureau at the CDC and Kaiser engaged in an “innovative collaborative partnership” to coordinate the national obesity epidemic agenda.

Bookmark and Share