Exercise in pregnancy has been a much often debated issue amongst the medical and fitness communities and each year sees new guidelines and approaches implemented to ensure expectant mothers feel safe and reassured to carry on, or even begin an exercise programme during their pregnancy. This post aims to give some of the background to the debate, the main issues raised and the research that leads to the guidelines that are then adopted by medical practitioners and health and fitness professionals.
Background and societal origins of debate on Exercise in Pregnancy
For long periods of human history women regularly performed hard physical work for long periods while conceiving, carrying, delivering and nursing their offspring without causing any harm to them. In many parts of the world of course, this is still the case. Similarly, mammals hunt and forage whilst pregnant and give birth to healthy offspring. Nature, seemingly has given us the means to carry on with our daily activities without having a detrimental effect on our young. So, why is their so much debate on how intense, how frequent and the type of exercise in pregnancy women should carry out to ensure that not only does their unborn child remain safe but they themselves don't suffer any adverse reaction.
The answer lies in our response to an unknown risk, which often times results in a knee-jerk response, the corollary being to try to avoid that risk which in this instance means the fear that exercise in pregnancy will harm the unborn baby. Of course, plenty of anecdotal evidence is used to support this fear, as there will be women who have been intense exercisers who have miscarried and this is then used as a possible cause of the miscarriage. However, the causes of miscarriages are complex and research is still ongoing to find all the possible causes. The end result of the debate has been by and large, a polarisation of views. The cautious, conservative viewpoint is that exercise in pregnancy will cause too many physiological changes that could be potentially harmful, so a restrictive approach to exercise is advocated. The more liberal approach is that exercise in pregnancy is not only good for expectant mothers, but an essential component in the life cycle. These polarised views inevitably generates a whole host of research into the subject, some of which is outlined in this post.
Research and Studies
Exercise, done at the right frequency and intensity causes an adaptive response to the cardiovascular and muscular-skeletal systems. Similarly, as any expectant mother can testify to, there are profound physiological changes to their bodies when they become pregnant. These adaptations cause changes among others, to the circulatory system and the muscular-skeletal system and it is here that scientists looked to produce factual evidence that could solve some of the complex answers in the 'excercise or not to exercise' debate and more importantly, the effects exercise would have on the unborn child.
Pivarnalk et al. 1994 demonstrated that the plasma volumes, red cell volumes and total blood volumes of regularly exercising women during pregnancy are at least 10 -15 per cent higher than those that didn't. This means that women who exercise regularly during pregnancy have more circulatory reserve, which improves their ability to deal with both anticipated (exercise and work) and unanticipated circulatory stress (haemorrhage, trauma). Clapp in his book 'Exercising Through Your Pregnancy'* states that starting regular, moderate-intensity exercise in pregnancy will limit weight gain and fat deposition. However, another study suggested that high levels of physical stress in the workplace during pregnancy are associated with an increased rate of pregnancy complications, including premature birth ( Clapp 1996c; Luke et al. 1995; Mamelle, Laumon, and Lazar 1984).
Researchers at the Harvard School of Public Health have demonstrated that physical activity before pregnancy can lower the risk of gestational diabetes by a half and that exercise in early pregnancy cuts the risk by a quarter. Another study at Kansas University has suggested that babies whose mothers do aerobic exercise during pregnancy may have healthier hearts and more mature nervous systems. The so-called womb-workouts may have health benefits that continue into adulthood, lowering the risk of heart disease, stroke, diabetes and hypertension later in life. These baby benefits are backed up by research in Auckland, New Zealand, which has shown exercise in pregnancy can prevent excessive birth weight in babies, resulting in fewer risks during birth and reducing likelihood of later obesity in the child. Norwegian research, published in Obstetrics and Gynaecology in Sept 2009 discovered that the odds of delivering a too-big baby dropped by as much as 28 per cent in women who exercised regularly in their second and third trimesters during their first pregnancy.
As some of the above studies have demonstrated it seems that exercise in pregnancy performed by women undergoing a normal pregnancy is associated with very little risk, may decrease a woman's risk of complications during pregnancy (hypertension, gestational diabetes) and may enhance weight loss post partum. However, there is still some reluctance in some quarters to trust the mounting body of evidence which continually supports the benefits of exercise in pregnancy. Perhaps, the plethora of information, like much in the often conflicting world of health and fitness has lead to confusing messages about the type, frequency and intensity that exercise sessions should be to ensure some of the benefits outlined above are guaranteed. The next part of this blog post will look deeper into the exercise prescription of expectant mothers.
* 'Exercising Through Your Pregnancy' , James F. Clapp, M.D.