MCHB/EPI Miami Conference — December 7 - 9, 2005

Weight Matters — Transcript

DR. SUZANNE TOUGH: Good morning. I'd like to speak to you today on what Jenny just articulated, body mass index on the firstborn baby. And I'd like to acknowledge my collaborator, Karen Tofflemire , in this work.

My objectives today will be to describe the characteristics of women according to their pre-pregnancy body mass index, and to assess this relationship between pre-pregnancy BMI and pregnancy complications, infant birth weight, and pre-term delivery, and as well to describe weight gain during pregnancy based on the ILM guidelines for BMI, and then again assess the relationship between weight gain and infant birth weight.

This data was collected as part of a stratified random sample of just over 1,000 women selected from two of the largest urban centers in Alberta , Calgary and Edmonton , each with a population of about a million people. The data was collected in the context of understanding what women knew and understood about reproductive risk at different ages of childbearing, and we also had the opportunity to ask them a little bit about their own pregnancy experience. Women were contacted within eight months of giving birth to their first child, and after informed consent, participated in about a 25-minute phone interview. So the data I'll speak to today is self-report. The statistical analysis was frequencies and bivariate, and then some regression modeling.

So what were the characteristics of these women, according to their pre-pregnancy BMI? Well, 66 percent of the women had a normal BMI as defined by a BMI of 18.5 to 24.9. Nineteen percent would have been defined as overweight, based on a BMI of 25 to 29.9. Ten percent as obese, based on a BMI greater than 30. And five percent were underweight, based on a BMI less than 18.5 at conception.

The obese women, as was noted in the first population, were more likely to be older, to have a lower education, which in this population was defined as not completing university or some kind of graduate training, to have been diagnosed with depression and/or anxiety in the year prior to conception, and more likely to have rated their physical health as poor in the twelve months prior to conception.

The obese women were significantly more likely compared to women of normal body mass index to experience pre-eclampsia with an odds ratio approaching two, and to have experienced gestational diabetes with an odds ratio approaching 14. And this I think was noted in our past presentations as well. And these odds ratios are adjusted for age, education, income, ethnicity, and prior history of depression.

We were interested in how long it took women to conceive. And although most women conceive within 12 months of trying, obese women took significantly longer to conceive than those of normal body mass index, among those planning a pregnancy. And in this population, almost 80 percent of women were planning to become pregnant. So 19 percent of obese women required some assistance to conceive, compared to eight percent of women with normal body mass index. In Canada , assisted reproductive technology is not part of our publicly funded health care system, so it's a user-paid phenomenon. As well, compared to women of normal body mass index, women who were underweight or overweight were significantly more likely to require assistance. Although the absolute difference is small. Difference between eight percent and about 10 percent.

So how did the babies look? Well, as also was reported earlier, women who were obese were significantly less likely to deliver a low birth weight or pre-term infant. Our provincial average rate of low birth weight delivery is about 5.8 percent, 5.8 to 6 percent depending on a three-year rolling average. And our pre-term delivery rate is 9.3 to 10 percent.

So what did weight gain during pregnancy look? Well, 71.8 percent of the women gained between 6.8 and 18.2 kilograms during the pregnancy period. And this is what's the recommended guideline for weight gain by our society of obstetricians and gynecologists. However, if we use pre-pregnancy BMI as a guideline for pregnancy weight gain, for our singleton pregnancies in this sample, overall, 21 percent of women gained less than would have been recommended, and 41 percent gained more than recommended based on their pre-pregnancy BMI.

As is noted in the table here, among women with a low pre-pregnancy body mass index, 27.3 percent failed to gain the recommended amount of weight during pregnancy. Among women with a body mass index greater than 27, 60 percent gained more than the recommended amount during pregnancy. And just of note, about 37 percent of those in the normal pre-pregnancy BMI gained the recommended amount during their pregnancy.

How did weight gain look based on pre-pregnancy BMI? Overall, about 10.8 percent of women who failed to gain the recommended amount of weight during pregnancy have a low birth weight infant. And again, I mentioned, our provincial average is above 5.8 percent. However, most at risk were women with a low pre-pregnancy BMI, who also gained less than the recommended amount. Overall, about 16 and a half percent of women who gained more than the recommended weight for their body mass index had a macrosomic infant, compared to about 6 percent of those who gained within the recommended guidelines. Although apparent among all women, even among women with a low pre-pregnancy body mass index, gaining in excess of the recommended amount increased their risk for macrosomic delivery. And this just articulates what I've just said, based on the graphs. About 10.8 percent of women who gained less than recommended, gave birth to a low birth weight infant, compared to 4% of women who gained the recommended amount of weight. Overall, 16 and a half percent, who gained more than what was recommended, delivered a macrosomic infant, compared to six percent of those who gained within the guidelines.

So just in summary, a high body mass index had a negative effect on reproduction, and was associated not only with pregnancy complications, but with delays in conception, an increased risk of excessive weight gain, and macrosomia. Pregnancy weight gain outside the recommendations based on pre-pregnancy body mass index had negative effects on infant birth weight, including increased risks for either low birth weight or macrosomia.

So some of the public health implications could include the following. Weight loss programs should be encouraged for obese women with infertility problems, and healthy weight gain should be encouraged for all women of childbearing age. Finally, particular attention should be given to pre-pregnancy body mass index, and recommended weight gain during pregnancy. I'd just like two of knowledge and some of my collaborators on the larger study, as listed here, and to thank you all for the opportunity of speaking about this today.