# Exercise as it relates to Disease/Physical Activity in the Prevention of Gestational Diabetes

The following text is an analysis of the journal article "A Prospective Study of Pregravid Physical Activity and Sedentary Behaviours in Relation to the Risk of Gestational Diabetes Mellitus", written by Zhang et al (2006). This critique has been written by a student (ID: u3100416) of the University of Canberra for the purpose of an assignment.

## Background to Research

Gestational Diabetes Mellitus (GDM), a sub-group of diabetes occurring during pregnancy, is characterised by a lack or resistance to insulin resulting in high blood glucose levels. GDM affects 5-9% of Australian females. During pregnancy the placenta releases hormones that makes the mother resistant to insulin so nutrients can reach the foetus. To combat this the mother must make 2-3 times the amount of insulin. If her body cannot do this or she remains resistant, a diabetic state occurs.
GDM puts the mother and baby at increased risk of:
Baby:
* Excessive birthweight
* Pre-term birth
* Future Type II Diabetes (T2DM)
Mother
* High blood pressure
* Pre-eclampsia
* Future T2DM
Modifiable risk factors of obesity and pre-gravid physical activity have been identified however, current data lacks methodological rigor; small samples and short-term follow-up. This article aimed to rectify this and determine if greater pre-gravid physical activity had a preventative effect on incidence of GDM.

## Where is the research from?

The study utilised data obtained from the Nurses’ Health Study II (NHS2) sample. In the United States, nurses were invited to provide data to identify risk factors for the development of chronic diseases. Places of recruitment include:
* Pennsylvania
* Texas
* California
* Carolina
* Connecticut
* Iowa
* Indiana
* Kentucky
* Ohio
* Massachusetts
* Michigan
* Missouri
* New York
This sample may not be a true representation of the population as volunteers, especially those with health education, are commonly more health conscious.

## What kind of research was this?

Occupying Level II in the hierarchy of evidence, a prospective cohort trial was the conducted method.
A prospective cohort trial is conducted as follows:
* Participants with similar characteristics are chosen and identified as a cohort (pregnant women in NHS2)
* Measures and follows differences between participants (levels of physical activity)
* Differences between outcomes observed and related to baseline differences (incidence of GDM)
Table 1 - Advantages/Disadvantages of a Prospective Cohort Trial
| Advantages | Disadvantages |
| Longitudinal - Can determine cause-effect relationship - Addresses gap in literature | Hard to follow large sample for long time period - Loss at follow-up can introduce bias |
| Observational - Research personnel bias less likely | Expensive and time consuming |
| Prospective - Not affected by recall error - Avoid selection bias at enrollment | Potential for confounding unmeasured factors |
| Large sample size - Addresses gap in literature - Improves results' statistical strength | |
| Can calculate incidence rates | |

## Research Method

21,765 females from the NHS2, identified at least one pregnancy and passed exclusion criteria, thus forming the sample.
Prior to pregnancy mailed physical activity questionnaires were answered regarding average:
* Time spent on recreational activities and walking per week
* Number of stairs climbed daily
* Intensity/pace
Diagnosis of GDM was based on self-report information gathered on a different questionnaire.
Table 2 - Advantages/Disadvantages of the Method
| Advantages | Disadvantages |
| Large sample size | Volunteer participant recruitment |
| Identification of risk factors when participants healthy - Reduces risk of participant bias & memory/recall error | No objective outcome measures (self-report outcome measures) - People commonly over-report amount of physical activity performed & under-report diseased-states |
| Mailed questionnaires | |
| Reproducible | |

## Results

After 10 years follow-up the following results were found:
* Of 21,765 pregnancies, 1428 incidents of GDM
* Greater quantity and intensity of pre-gravid exercise significantly reduced the risk of GDM (RR = 0.71, p-value = <0.001)
* Increased walking pace and stair climbing was associated with a reduced risk of GDM (RR = 0.6, p-value = 0.004 and RR = 0.44, p-value = 0.003 respectively)

## Conclusions

Increased physical activity prior to pregnancy is significantly associated with a reduction in GDM risk. Furthermore greater walking pace and number of stair flights climbed had a significantly lower risk of GDM.
The longitudinal, prospective nature of this study provides it with good internal validity. However when interpreting both the results and conclusions recall that the sample selected may be at risk of volunteer bias, affecting external validity of the study. Meanwhile the use of solely subjective outcome measures potentially makes the results appear deceivingly more favourable.
Much of the surrounding literature focuses on physical activity as an intervention following the diagnosis of GDM however one meta-analysis in 2010 examined the effect of physical activity both during and prior to pregnancy. The aforementioned findings were supported, suggesting pre-gravid physical activity reduces the risk of GDM and its associated adverse risks. Conclusions by the authors suggested this reduced risk of GDM is mediated by improved insulin sensitivity.

## Practical advice

The findings support that physical activity should be employed prior to pregnancy to reduce the risk of the incidence of GDM and thus its associated complications. Health professionals should encourage women of all ages to participate in regular physical activity as per the guidelines provided in the Further Reading section of this article.
The provided physical activity guidelines are based on a non-pregnant population. If pregnant a GP should be consulted for recommendations on appropriate physical activity participation.
If commencing physical activity a pre-exercise screening tool, such as the one found at https://www.essa.org.au/wp-content/uploads/2011/09/Screen-tool-version-v1.1.pdf should be completed and advice from a GP sourced if necessary.
Cease exercise and consult your GP if any of the following symptoms are experienced during exercise:
* Chest pain
* Shortness of breath
* Lightheadedness
* Joint pain

## Further information/resources

Below further information regarding GDM and exercise are provided:
GDM - Diabetes Australia
Physical Activity Guidelines - Australian Government
Consult your GP for additional information or questions.

## References

* 1 2 Zhang, C., Solomon, C., Manson, J., & Hu, F. (2006). A Prospective Study of Pregravid Physical Activity and Sedentary Behaviors in Relation to the Risk for Gestational Diabetes Mellitus. Journal Of The American Medical Association, 166(5), 543-548.
* 1 2 3 4 Buchanan, T., Xiang, A., Kjos, S., & Watanabe, R. (2007). What Is Gestational Diabetes?. Diabetes Care, 30(Supplement 2), S105-S111.
* ↑ Diabetes Australia,. (2016). Gestational Diabetes. Ndss.com.au. Retrieved 19 September 2016, from https://www.ndss.com.au/gestational-diabetes
* ↑ Salzer, L. & Yogev, Y. (2014). Gestational diabetes. United Kingdom: Taylor & Francis Group.
* 1 2 American Nurses Association,. (2013). Nurses' Health Study 2 - Nurses' Health Study. Nhs3.org. Retrieved 21 September 2016, from https://www.nhs3.org/index.php/our-story/20-nurses-health-study-2
* 1 2 3 Hoffmann, T., Bennett, S., & Del Mar, C. (2013). Evidence-Based Practice Across the Health Professions. London: Elsevier Health Sciences APAC.
* ↑ Tobias, D., Zhang, C., van Dam, R., Bowers, K., & Hu, F. (2010). Physical Activity Before and During Pregnancy and Risk of Gestational Diabetes Mellitus: A meta-analysis. Diabetes Care, 34(1), 223-229.
* ↑ Harvard Publications,. (2015). Safe exercise: Know the warning signs of pushing too hard - Harvard Health. Harvard Health. Retrieved 26 September 2016, from http://www.health.harvard.edu/pain/safe-exercise-know-the-warning-signs-of-pushing-too-hard