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)