Main Findings and Interpretation
In our study we focused on the difference in baseline characteristics
and pregnancy outcomes between obese pregnant women diagnosed with GDM
who lost weight or gained up to 5 kg compared to those who gained the
IOM recommended weight of 5-9kg. A secondary analysis evaluated the
differences between all 3 groups in our cohort: women with GWG
<5kg, those with GWG of 5-9 kg and women with
GWG>9 kg. We did not further subdivide the groups according
to obesity category because that would have generated a very small
number of study participants in each subcategory. To our knowledge, this
study is one of a few aiming to investigate the relationship between
high maternal pre-pregnancy BMI and GWG outwith the IOM recommendations.
Few studies have specifically addressed weight loss or insufficient GWG
in pregnancy, as this is generally not promoted in pregnancy (23-28).
Our study did not find higher rates of SGA or early prematurity in women
with weight loss or insufficient GWG. A retrospective study (23) found
that weight loss in obese pregnant women diagnosed with GDM is
associated with higher odds for SGA (aOR 1.69, 95% CI 1.32–2.17) and
preterm delivery <34 weeks (aOR 1.71, 95% CI 1.23–2.37).
This study, despite having a very large cohort, used different GDM
diagnostic criteria (Carpenter and Coustan) to our study (IADPSG) and
had a different population profile in terms of baseline characteristics;
their study included overweight and obese women while our study focused
only on obese only women. Similar to the findings of these authors, we
found higher rates of prematurity in women with weight loss/insufficient
GWG treated with diet alone, but this was not statistically significant
on adjusted logistic regression. Our finding that weight loss after a
GDM diagnosis in obese women is not associated with a lower birth weight
is supported in a recent study by Katon et al (25). However, the
latter study had a relatively small sample size and did not analyse
markers of foetal growth such as SGA and LGA. Bauer et al (26)
also found no increased odds for SGA or prematurity in obese GDM women
who lost weight or maintained their weight during pregnancy. Recently,
Kurtzhals et al (29) found improved foetal growth in women with
restricted GWG with no increased rates of SGA or LGA. A direct
comparison to our study findings however is difficult as women were
diagnosed by the Danish Criteria which are higher compared to the IADPSG
criteria, the baseline BMI was self-reported with an inevitable risk of
recall bias and women were not stratified according to their BMI.
Conversely, in our population of obese women with GDM, the rates of LGA
babies were higher in those who lost weight or gained <5kg as
compared to women who gained 5-9kg although this difference was
eliminated on logistic regression analysis. This may be due to the
higher baseline BMI in the GWG <5kg group suggesting that in
our population pre-pregnancy BMI has a greater impact on foetal growth
not compensated by weight loss or minimal GWG during pregnancy. This
finding albeit controversial, is supported by other studies (30-32).
Another interesting finding was the higher rates of PPH and
polyhydramnios in GDM women with low GWG although again the significance
is lost on adjusted logistic regression. It is known the polyhydramnios
is associated with higher rates of PPH due to uterine stretching. The
current literature examining the link between obesity and PPH is
contradictory (33, 34). Studies that have assessed potential links
between weight loss in obese women (without GDM) and PPH (27, 35) found
no association. A recent study (23) found improved rates of
polyhydramnios in obese GDM women with weight loss but this study
concentrated on gestational weight change related outcomes in a BMI
heterogenous population and there was no sub analysis on obese only
study participants.
In evaluating adverse outcomes between women who gained insufficient
weight, women who gained 5-9 kg and women who gained >9kgs,
we found that women in the first group were older and had a higher
pre-pregnancy BMI compared to the other 2 groups, this finding is
supported by others (23, 36). Moreover, and supporting the results of
our primary analysis, the insufficient GWG group had higher rates of
polyhydramnios and PPH, even compared to the excessive GWG group but
lost on adjusted logistic regression analysis. A recent study (37) found
higher rates of polyhydramnios in euglycemic women that were older and
had higher pre-pregnancy weight gain. Another study (38) also found
higher rates of polyhydramnios in women with a higher pre-pregnancy BMI.
These studies were not restricted to GDM patients but complement the
results of our study and suggest that baseline BMI may plays a greater
role in the physiopathology of polyhydramnios beyond dysglycemia and
GWG.
Women with excessive GWG had higher rates of PIH, macrosomia and LGA and
this is supported by a large body of current literature ((23, 27, 39,
40)