Being pregnant and giving birth are physically demanding. Having a reasonable level of fitness will help you manage your changing body shape as well as the demands of pregnancy, birth and early parenting.
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A reasonable level of fitness will prepare you both physically and emotionally for labour. Fitness refers to your stamina, strength and flexibility. The best way to get fit is through regular physical activity at an intensity that pushes you to work at a moderate pace, but not to the point of being out of breath.
To achieve and maintain a reasonable level of fitness aim for one of the following:
- a session of moderate-intensity exercise on all or most days of the week
- at least 150 minutes of exercise over a week
- 10,000 steps per day.
Your changing body and exercise
Weight gain and altered posture are two obvious physical changes that happen during pregnancy. Other changes are less visible.
Cardiac changes
To meet the increasing demand for blood supply to your growing baby, your heart enlarges and also pumps faster. This means you are already doing an aerobic workout just by being pregnant. It also means that you should moderate the intensity of your exercise as there is a smaller range between your resting heart rate and the safe maximum heart rate.
Circulation changes
The volume of your blood increases as your baby grows. A softening of the walls of your veins and the weight of your uterus in later pregnancy can affect the flow of blood to your heart, allowing it to pool in your legs. Calf raises and walking on the spot while you are exercising in a standing position will encourage the flow of blood back to your heart and help to prevent light-headedness. Support stockings can also help if you are prone to feeling light-headed or if you have varicose veins.
After 16 weeks of pregnancy, it is best to avoid exercises lying on your back as the weight of the baby can press on major blood vessels returning blood to the heart and also cause you to feel light-headed or nauseous. It is also recommended to sleep on your side in the second half of your pregnancy. If you wake to find yourself on your back, trust that your body has woken you in order to move to a better sleeping position.
Getting too hot
Your body’s temperature is naturally slightly higher when you are pregnant. Intensive exercise may cause your core temperature to rise to an unsafe level for your baby. Take these simple precautions:
- Limit the effort of your exercise to ‘moderate intensity’.
- Drink water before, during and after exercise.
- Wear lightweight clothing.
- Exercise in a cool ventilated environment (no spas or saunas).
- Avoid exercise if you have a fever.
Joint changes
Pregnancy hormones cause a change in the structure of the ligaments that support your joints so that they are softer. This, along with changes in your posture and weight gain, can increase the need to protect your joints during pregnancy, especially when you exercise. The joints most affected are pelvis and lower back. Other commonly affected joints are in the upper back, feet and wrists. If any of them are painful or causing you to 'waddle', a physiotherapist can give you specific muscle-strengthening exercises that may help.
To protect your joints:
- Avoid high-impact exercise such as netball, tennis, aerobics or running.
- Exercise in a pool or a fitball class, rather than walking long distances or doing a gym class.
- Wear supportive shoes.
- Take shorter strides when you walk.
- Bring your knees together when changing positions.
- Change positions in a controlled and smooth way.
- Maintain good posture during all your exercises to avoid joint strain.
Exercise in pregnancy
Exercise during pregnancy is good for you. It can:
- provide an overall sense of wellbeing
- give you more energy
- help you to manage your weight
- build abdominal, back and pelvic floor strength to support your growing weight
- help your body adapt to the physical changes that come with pregnancy
- give you greater confidence in your body’s ability to give birth
- help you to get you get back into shape after the birth.
Will exercise harm my baby?
Exercise will not harm your developing baby as long as you exercise at a safe level. It is more risky for your baby if you are overweight. Moderate exercise regularly is preferable to occasional intense exercise.
When and what to exercise to avoid in pregnancy
You should avoid exercise in pregnancy if you have the following medical condtions:
- your waters have broken (ruptured membranes)
- uncontrolled high blood pressure
- pulmonary or venous thrombus
- low lying placenta (placenta praevia) in late pregnancy
- intra-uterine growth retardation
- incompetent cervix
- uterine bleeding
- pre-eclampsia.
Sport and activity to avoid in pregnancy
Some sports and activities need to be avoided in pregnancy. These include:
- sports or activities where there is a risk of collision, tripping or falling, or heavy body contact
- competitive sports where you have to reach, stretch or leap beyond safe limits
- activities an unsafe environment, such as high temperatures (spas or hydrotherapy pools or 'hot' yoga) or involve heavy equipment (weightlifting, water and snow skiing, scuba diving)
- repetitive high impact exercise, or with lots of twists and turns, high stepping or sudden stops that cause joint discomfort.
If you are new to exercise, start slowly and progress at your own pace, and at an intensity that makes you feel good.
Be alert to any signs that you may need to stop exercising such as:
- vaginal bleeding
- nausea or vomiting
- feeling faint or light-headed
- strong pain, especially from your pelvis or back
- reduced movement of your baby.
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The Women’s does not accept any liability to any person for the information or advice (or use of such information or advice) which is provided on the Website or incorporated into it by reference. The Women’s provide this information on the understanding that all persons accessing it take responsibility for assessing its relevance and accuracy. Women are encouraged to discuss their health needs with a health practitioner. If you have concerns about your health, you should seek advice from your health care provider or if you require urgent care you should go to the nearest Emergency Dept.
Maternity care provider clinicians have been aware for many decades that maternal supine position and pregnancy are not a good mix. This is probably because when the woman lies on her back the gravid uterus is known to compress the inferior vena cava (Kerr et al. 1964). This can result in a range of negative sequelae such as maternal hypotension and reduced blood flow to the fetus (Holmes, 1960). Because this phenomena is so well known, standard practice is for clinicians to avoiding placing the woman in supine position for routine examinations and procedures, moving the woman into left lateral if there are signs of fetal distress in labour and also advising her to avoid the supine position herself, at least during the day (Thurlow & Kinsella, 2002).
More recently there is emerging evidence that if the woman sleeps on her back that this puts her at increased risk of stillbirth (Stacey et al. 2011; Owusu et al. 2013; Gordon et al. 2015). This is biologically plausible because of what is already known about negative sequelae of the woman adopting this position during the day.
In this issue of The Journal of Physiology Stone and colleagues (2017) have added an important piece to the puzzle of understanding the physiology of maternal supine position and fetal response, by conducting a controlled experiment monitoring both the mother and fetus during the day. In this ground‐breaking study they avoided ‘high risk’ women with comorbidities and also did not monitor their participants during sleep. In doing so they had probably as clean a look as is currently possible at the human fetus's response to the maternal supine position when compared to the same fetus spending the same time with the mother lying in other positions.
It is very interesting that they found an increased likelihood of fetal quiescence in the supine position especially as this was in a group of normal healthy late third trimester pregnancies. As they show, this finding suggests that the well fetus is able to mount an adaptive response to this potential stressor by shifting to a lower oxygen consuming state. If they have found this in the well fetus, during a 30 min period in the supine position, with the mother awake, one can only speculate as to what might occur in a vulnerable fetus, whose mother is sleeping supine for several hours during the night.
Stone et al. conclude, ‘The supine position may be disadvantageous for fetal wellbeing and in compromised pregnancies may be a sufficient stressor to contribute to fetal demise.’ This fits well with the triple risk model for stillbirth, illustrated below (Fig. 1), whereby a vulnerable fetus (perhaps one that is growth restricted) with maternal comorbidities such as age, obesity, parity, gestational diabetes, gestational hypertension, etc., encounters a fetal stressor such as supine sleep position and cannot adapt to repeated nightly exposure to this stressor and ultimately dies as a result.
These results certainly support the findings from earlier epidemiological studies, that supine sleep in pregnancy increases the risk of stillbirth, particularly in the growth‐restricted fetus. In addition, they provide important new information towards understanding the physiology of fetal responses to this position. Further research that examines the vulnerable fetus's response to maternal supine sleep position overnight is warranted. In the meantime, perhaps it is time for maternity care providers not only to act to avoid maternal supine position during the day but also to alert pregnant women to avoid the supine sleep position in the third trimester of pregnancy.
The author has approved the final version of the manuscript and agree to be accountable for all aspects of the work. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed.
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