WEIGHT GAIN IN PREGNANT WOMEN

By

Cathy House

WHAT WAS THIS RESEARCH ABOUT?

Objective: To generate reliable new reference ranges for weight gain and increase in body mass index (BMI) during pregnancy from a large population.

WHY WAS THIS STUDY DONE?

Common problems with published reference values for weight gain during pregnancy included outdated charts based on a population about 50 years ago in which accurate gestational age assessment was lacking.

Previous research used a small sample size.

STUDY DESIGN

Was is prospective or retrospective?

Answer: prospective

Why? It was looking to see how much weight would be gained.

• How large was the sample size?

Answer: 4034 women. (3242 Caucasian, 578 Asian, 214 Black)

WHAT WAS DONE TO MAKE THE RESULTS MORE ACCURATE?

Eliminated risk factors. Exclusion criteria were uncertain gestational age, emergency referrals and known insulin-dependent diabetes millitus were excluded.

WHAT DO YOU THINK ABOUT THIS SAMPLE SIZE?

Large sample, but heavily Caucasian. The data produced would be more accurate for the large Caucasian population as opposed to the small Asian and Black populations.

The data was not entirely representative of all races, but it was meant to represent a population.

Centile curves were done to try and represent other races.

HOW WAS THE DATA PRODUCED?

Was this an observational study or an experiment?

Answer: Observational Study

How do we know this?

The variable of interest was recorded as it naturally occurred.

VARIABLES

What was the MAIN variable of interest?

Answer: Weight gain

Was this quantitative or categorical?

Answer: Quantitative because it was the amount of weight gained at each time measured. This is also the response variable.

What was the explanatory variable?

Answer: Pre-pregnancy BMI

WERE THERE OTHER EXPLANATORY VARIABLES?

This study involved several variables that could have been used to explain weight gain.

Although the main explanatory variable was BMI and the main response variable weight gain, what other variable showed an impact in this study?

Answer: Parity (childbearing history)

OTHER FACTORS

Although the main variable here was weight gain at different times during pregnancy, factors such as age, race and socioeconomic status were involved. Because this was an observational study and not an experiment, these factors were not manipulated.

ANALYZING THE DATA

Refer to Table 2 How was the data summarized in the article?

Answer: Mean. Mean weight gain was 15.5 +/- 5.9 kg at term with values >25.4 kg and <5.7 kg for the 95th and 5th centile, respectively.

The standard deviation was 12 kg for Caucasians, 10.1 kg for Asians and 12.2 kg for Blacks.

DISPLAYING DATA

Caucasians

DISPLAYING DATA

Fig. 3. Weight gain 50th centile curves in Caucasians (continuous line) and Asians and Blacks (dashed line).

DISPLAYING DATA

Fig. 4. BMI 50th centile curves in Caucasians and Blacks (continuous line) and Asians (dashed line).

RESULTS

Blacks had consistently lower weight gain and BMI than Caucasians over the whole period. These differences were statistically significant for weight gain (P < 0.0001) but not for BMI (P = 0.66). Variance of SDS for weight gain was larger than 1, probably due to more frequent extreme values. The variance of SDS for BMI was 1.14 and did not deviate systematically from Caucasians. Thus, BMI norms of Caucasians can be used for Blacks, whereas 1.5 kg have to be added to weight gain values to apply Caucasian norms.

BIAS?

Is there reason to suspect bias?

Not really. It was an observational study that wasn’t out to “prove” anything, but rather to provide useful information for women.

MORE RESULTS

Found a mean weight gain of 15.5 ± 5.9 kg (34.2 ± 13.0 lb) at term with a value of 5.7 kg (12.6 lb) and 25.4 kg (56.0 lb) for the 5th and 95th centile, respectively. The distribution of weight gain showed a larger spread than reported in the 1970s and. This may be due to the large changes in dietary habits over the last 30 years. Thus, recently published studies confirm the wide range of total pregnancy weight gain with a mean weight gain of 16.1 ± 6.4 kg or 16.8 ± 4.9 kg. Weight gain was lower in Asians and Blacks than Caucasians.

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