Exercise as it relates to Disease, Does recreational physical activity during pregnancy reduce the risk of preeclampsia?

This is a critique of a study assessing "Recreational Physical Activity During Pregnancy and Risk of Preeclampsia" conducted by Tanya K. Sorensen et al.[1]

What is the background to this research?

Preeclampsia is a hypertensive disorder resulting in an increase to the mother's blood pressure during pregnancy [2]. It occurs in around 5% of pregnancies and is most common after 20 weeks of gestation [2]. If left untreated, preeclampsia can have serious health implications for both mother and baby including hemolysis, elevated liver enzymes and low platelet count (HELLP syndrome), poor blood flow to the placenta, placental abruption, eclampsia, and cardiovascular disease [2], [3].

Physical activity (PA) is known to have positive benefits on reducing health risks such as coronary heart disease, type two diabetes and hypertension however, little is known if there is a positive relationship between maternal PA and the risk of hypertensive disorders, including preeclampsia [1].

This article aims to identify if PA during the year before pregnancy and in the early stages of pregnancy reduced the risk of preeclampsia [1].

Where is the research from?

The study was conducted at Swedish Medical Centre in Seattle and Tacoma General Hospital, Tacoma, USA between April 1998 and June 2001 [1].

The procedures used in the study complied with the protocols approved by the institutional review boards of the participating hospitals.

This study was funded in part by the National Institutes of Health and the Maternal and Child Health Bureau, Health Resources and Services Administration, Department of Health and Human Services [1]. Technical expertise was provided by Ihunnaya Frederick and Raymond Miller, both reputable U.S. researchers in an associated field. There is no obvious conflict of interest or bias evident between researchers, participants, and sponsors [1].

What kind of research was this?

An observational case-control study was used to determine if an exposure is associated with an outcome [4]. This type of study is quick, inexpensive and simple to conduct, poses no risk to participants and can use a small sample size, however, can be subject to different forms of biases, particularly if responses or record keeping are inaccurate [4].

What did the research involve?

Method

584 pregnant women participated in the study. The study used procedures approved by both participating hospital and were in accordance with ACOG guidelines which defined preeclampsia as "sustained pregnancy-induced hypertension with proteinuria" (elevated levels of protein present in the urine) [1], [5]. The 201 preeclamptic and 383 normotensive women who participated provided written consent.  Women with eclampsia or HELLP syndrome were not included [1].

A questionnaire was utilized during the participants postpartum hospital stay which collected information on medical, reproductive, maternal sociodemographic and lifestyle characteristics [1]. Questions relating to PA during pregnancy were limited to the first 20 weeks of pregnancy as preeclampsia typically occurs after that [1], [2].

Participants were asked about their height and weight during the 3 months prior to their pregnancy as well as their PA in the year before their pregnancy including[1]:

• Frequency
• Average time spent
• Walking speed (< 2, 2, 3-4 or > 4mi/h)
• Distance (miles) walked daily
• Flights of stairs climbed daily

Participants were categorized as being 'active' or 'non-active' depending on their participation in PA during the first 20 weeks and year before pregnancy . Participants who were active were then grouped according to ;

1.   Time engaged (hours per week)
2.   Intensity (MET scores)

o   Light: < 3

o   Moderate: 3 to < 6

o   Vigorous: 6

o   Maximal > 6

3. Energy expended (MET hours per week)

Other variables such as age, race/ethnicity, education, smoking status and BMI were considered which is important to enable a more accurate analysis of the research findings and ensure any benefit from the findings are applicable to a wider cohort of women [1].

Limitations

The study involved the participants self-reporting their PA. This can cause recall bias and inaccuracies [6]. Participants could potentially forget PA for a certain week/s or a specific event that may have occurred affecting their ability to participate in PA. Similarly, some participants could have provided inaccurate responses to the questionnaire, falling under response bias [7]. The authors attempted to mitigate the likelihood of this occurring by using well-trained interviewers to collect information [1].The authors also stated that some misclassification of PA duration, intensity and energy expended during participation may have occurred and that selection bias was possible [1]. A larger sample size would have provided more accurate mean values and identified any participants that could skew the data from a smaller sample [8].

What were the basic results?

This study found that women who were active in any regular PA during the first 20 weeks of pregnancy experienced a 35% reduced risk of preeclampsia compared to women who were inactive [1]. Those involved in light to moderate PA experienced a 24% reduced risk compared to 54% for women participating in vigorous activity [1]. Similarly, women who were physically active the year before pregnancy were associated with a 33% reduced risk of preeclampsia [1]. Women who engaged in PA the year before pregnancy as well as during the first 20 weeks of pregnancy experienced a 41% reduced risk of preeclampsia [1].

Vig - 54% Reduction | Light- mod - No Reduction
Vig - 60% Reduction |
| EE | Decreased as EE increased
>9 METS hrs/wk - 41% Reduction | Decreased as EE increased
21.9-36.8 MET hrs/wk vigorous - 57% |
| Walking | Distance - No association
Brisk walk (>3mi/h) - 30-33% Reduction | Distance - No association |
| Stairs | 1-4 flights - 29% Reduction | Inverse relationship |

What conclusions can we take from this research?

The results from this study suggest that participation in PA in the year before pregnancy as well as during the first 20 weeks of pregnancy has a positive association with a reduced risk of preeclampsia. Furthermore, the occurrence of preeclampsia tends to decrease with PA intensity and energy expended [1].  These findings are similar to an earlier study conducted by Marcoux et al. which found a positive correlation of 43% in a study of Canadian women [1].

Similar studies should be conducted in other countries to determine if location, environment, access to medical facilities and other factors provide different results.

Practical advice

Participation in PA has all kinds of health benefits [9]. The World Health Organization (WHO) states that adults should participate in at least 150-300 mins of moderate-intensity PA or 75-150 minutes of aerobic PA each week or a combination of both and muscle strengthening activities should be performed at least two days per week and sedentary time should be limited [9]. WHO recommends that pregnant women should do at least 150 minutes of moderate activity and incorporate a variety of muscle strengthening activities with reduced sedentary time but should avoid movements which could be harmful [9].

Further information/resources

For further information:

• Word Health Organization, PA - https://www.who.int/news-room/fact-sheets/detail/physical-activity
• PA and Exercise Guidelines for all Australians - https://www.health.gov.au/health-topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians\
• Australian Government Department of Health - Preeclampsia - https://www.health.gov.au/resources/pregnancy-care-guidelines/part-d-clinical-assessments/risk-of-pre-eclampsia
• Everything you need to know about preeclampsia -https://www.medicalnewstoday.com/articles/252025

References

• ↑ a b c d e f g h i j k l m n o p q r s t Sorensen, T., Williams, M., Lee, I., Dashow, E., Thompson, M. and Luthy, D., 2003. Recreational Physical Activity During Pregnancy and Risk of Preeclampsia. Hypertension, [online] 41(6). Available at:
• ↑ a b c d Felman, A., 2017. Preeclampsia: Causes, symptoms, and treatments. online] Medicalnewstoday.com. Available at: <[https://www.medicalnewstoday.com/articles/252025
• ↑ Mayo Clinic. 2021. Preeclampsia - Symptoms and causes. [online] Available at:
• ↑ a b Susan Lewallen, P., 2021. Epidemiology in Practice: Case-Control Studies. [online] PubMed Central (PMC). Available at:
• ↑ Cleveland Clinic. 2021. Proteinuria: Causes, Symptoms, Tests & Treatment. [online] Available at:
• ↑ Catalog of Bias. 2021. Recall bias. [online] Available at:
• ↑ Johnson, C., 2021. Response Bias: Definition, 6 Types, Examples & More (Updated). [online] Nextiva Blog. Available at:
• ↑ Zamboni, Jon. "The Advantages of a Large Sample Size" sciencing.com, https://sciencing.com/advantages-large-sample-size-7210190.html.
• ↑ a b c Who.int. 2021. Physical activity. [online] Available at:

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