Transcript Single Quantitative Variable

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outdated charts based on a population about 50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.
68-95-99.7 RULE