How Much is Enough: What The Research Tells Us About Pregnancy And Physical Exercise

By Ange

Want to hear a scary statistic?

Between 1994 and 2000, only 10% of pregnant women in the United States met the recommendation for regular, moderate-intensity exercise for at least 5 days a week.

And while I hate to reference data outside of Australia, I am certain these numbers hold true for us living ‘down under’.

In this article I want to unpack the possible reasons that account for these lower than recommended physical activity levels. Further, I want to do my part to help educate the next generation of pregnant women on why exercise is so important for everyone’s health outcomes; yours, your babies and future society.

What are the current physical activity recommendations for pregnant women?

In the absence of medical or obstetric complications you should aim to meet ‘the physical and sedentary behaviour guidelines for adults during pregnancy. This means being active most days, preferably every day, to a weekly total of either:

  • 2.5 to 5 hours of moderate intensity physical activity
  • 1.25 to 2.5 hours of vigorous intensity physical activity (Note: See below for current research on exercise above 95% VO2 max). 
  • an equivalent combination of moderate and vigorous activities.
  • Do muscle strengthening activities at least 2 days each week. Aim to do strengthening activities, such as light resistance training or bodyweight exercises.
  • Doing any physical activity is better than doing none. If you do no physical activity right now, start by doing some, then slowly build up to the recommended amount’.

(The Australian Government Department of Health)

Why are the recommendations not being met?

While the reasons that account for low levels of physical activity across a population can be diverse and multi factorial, changing and challenging out-dated beliefs continues to be a leading cause.

Put simply, many women are still unsure if it is safe to exercise while pregnant and are possibly unclear or what are the specific benefits to their unborn babies.

Unfortunately, many obstetric care providers fail to have the specific knowledge, which prevents them from being able to educate their pregnant patients fully.

The result of this lack of information, is that many women might hold out-dated beliefs, be worried or fearful or even complacent. If they were previously active, they might have concerns about how to modify their exercise program to meet their new demands or if they were inactive, worry that a new exercise ‘regime’ may be too much.

We also continue to see they spread of misinformation from sometimes well meaning, but ill-informed older generations that questions the safety of exercise.

Modest aerobic exercise training improves fetal outcomes

A study from Clapp et al (2000) investigated how exercise can greatly improve fetal outcomes through increased placental performance, plasma and blood supply. This study involved a control group (non- exercising) and an intervention group, which was engaged in weight-bearing exercise for 20 minutes 3 to 5 times a week at 55% to 65% intensity of their preconception aerobic capacity from 8 to 9 weeks until delivery.

The outcomes of the study showed that:

  1. Exercise increased fetoplacental growth rate and ulti- mately size at birth.
  2. Increased placental growth was documented as early as 20 weeks and persisted through the pregnancy.
  3. The exercise group had placentas with significantly greater functional volume, nonfunctional volume, villous volume, and terminal villi.
  4. The increased fetal growth was symmetric with the intervention group having larger newborns with greater lean body mass than the control group. 

Miscarriage, preterm delivery and birth weight extremes

Madsen et al (2007) from the Danish National Birth Cohort analysed the prospective risk of miscarriage up to 22 weeks of gestation in 92671 pregnant women reporting physical activity. They found that there is no dose effect with miscarriage among all levels of activity compared with sedentary women. The Norwegian Mother and Child Cohort Study (MoBa) with 61098 pregnant women demonstated lower rates of preterm birth in women exercising 3 to 5 times per week at 30 weeks of gestational age. Further, moderate leisure time physical activity has also been proven to reduce the risk of larger than gestistational age babies by 30%. Another study from Clapp and colleagues confirmed that newborns of exercising women are leaner and have decrease body fat and higher lean body mass than newborns of non exercising women. 

Longterm impact on metabolism

There is a rapidly expanding literature to support the impact of in utero environment on adult health and the health of future generations. Exercise and diet while pregnant might not just decrease a woman’s risk of developing gestational diabetes, while promoting healthy weight gain, it might have a profound impact on the babies risk of developing metabolic disorders into their adult years. 

Foetal growth restriction is associated with adult metabolic syndrome, chronic hypertension, and type 2 diabetes mellitus. Maternal obesity and  diabetes, predict 2- to 3-fold risk in childhood and adult obesity and type 2 diabetes. 

What is even crazier is that there are strong links to suggest that metabolic dysfunction can cross generations and we can see heritable gene expression changes that are not due to primary alteration in DNA. 

Therefore the early foetal environment in utero can permanently program someone’s metabolic health later in life. A high-fat, high-fructose diet coupled with a sedentary lifestyle before and during pregnancy creates an in utero environment that sets the stage for future metabolic syndrome.

How much is too much?

For ethical reasons, most studies that measure the effects of intense physical exercise have not been conducted on humans, but rather on sheep or rats.  

But these studies do provide a framework that can be translated to human modelling, with 50-75% of VO2 maximum appearing as a safe intensity. Studies have indicated the exercise at 95% or above maximum V02 creates an elevated maternal sympathetic response, reduces placental blood flow, elevates maternal lactic aside, reduces glucose delivery and lowers maternal pH. It has also been shown that uterine contraction increase which could bring on pre-term labour and repeated maximal exercise significantly reduces fatal growth. 

When you should stop IMMEDIATELY!

There are few warning signs that indicate you should stop exercising immediately and seek specialist advice as soon as possible.

These include:

  • vaginal bleeding
  • amniotic fluid leakage
  • contractions more frequent than every 6 minutes
  • chest pain
  • irregular heart- beat
  • shortness of breath, dizziness or fainting
  •  calf pain or calf swelling
  • decreased fetal movement

Summary

I hope that by pulling together the findings from these key studies, it provides the research backed data to help get expecting mothers moving.

I know first hand, that on somedays I need nothing more than to take it easy and that they first trimester can be challenging. But if you are free from major health complications, incorporating regular physical activity into your day is a MUST. 

A key message from all these studies also indicated that doing something is better than nothing, you can see improvement in health and fitness during pregnancy and for those who were sedentary prior to pregnancy  can do so by starting at a low intensity (50% Vo2) with more rest.

If you are struggling to get moving, start with some daily stretches and gentle movement and aim to build from there. 

Check out our free download for 8 must-do daily stretches.

Reference List

  1. Clapp JF. In uence of endurance exercise and diet on human placental develop- ment and fetal growth. Placenta. 2006;27:527–534.
  2. Clapp JF, Kim H, Burciu B, Lopez B. Beginning regular exercise in early preg- nancy: e ect on fetoplacental growth. Am J Obstet Gynecol. 2000
  3. Madsen M, Jorgensen T, Jensen ML, et al. Leisure time physical exercise during pregnancy and the risk of miscarriage: a study within the Danish National Birth Cohort. BJOG. 2007
  4. Newton ER and May L. Adaptation of Maternal-Fetal Physiology to Exercise in Pregnancy: The Basis of Guidelines for Physical Activity in Pregnancy. 2017

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Our founder

Ange Drake is an personal trainer, women’s empowerment coach and fitness blogger in the northern suburbs of Melbourne. She is the director of one of the few womens’ only strength training gyms in Melbourne, 23W. Ange helps women to learn how to use strength based training, nutritional strategies and a positive mindset to transform their bodies, relationship with food and mind.

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