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Changes in the Body during Pregnancy

The information is based on U.S. guidelines.


Anatomical and physiological changes during pregnancy can affect the musculoskeletal system, both at rest and during physical exertion. The most obvious change is weight gain. The increased weight can lead to a greatly increased load on joints such as hips and knees, for example in connection with running. Such stress can lead to discomfort in healthy joints and increase the damage of people with previous joint injuries. A shift in the center of gravity causes pregnant women to become weaker in the back, which increases the risk of transient back pain.

Changes in the Body during Pregnancy

It has not been scientifically shown that the increased weight during pregnancy damages the joints. It has also not been shown that other pregnancy changes lead to muscle and skeletal damage in connection with physical activity during pregnancy. However, in case of complaints from the musculoskeletal system, pregnant women who exercise, or are very physically active, should talk about this with their midwife or doctor.


Measurements that have examined the activity of the uterus in women who exercise have not shown any significant changes in uterine muscle contractions during the last eight weeks of pregnancy. In cases where researchers have found increased contractions in the uterus during physical activity, the strength of these contractions has been low. There are no scientific points for strong physical activity to trigger premature delivery. However, women who have previously given birth prematurely, or who are at risk of premature birth, such as women bearing twins, are advised by the Council to reduce activity during the second and third trimesters of pregnancy. Visit Bestaah for quality and affordable maternity t shirts.

Nutritional needs

After pregnancy week 13, about 300 extra calories per day are required to cover the extra need that a pregnancy brings. The energy demand increases further with physical activity. During weight-bearing activities, such as walking, energy needs increase as the weight gain increases during pregnancy. Pregnant women burn more carbohydrates than non-pregnant women, which seems to be a normal consequence of pregnancy.

The heart and circulation

Pregnancy causes major changes in blood circulation. The changes mean increased blood volume, faster heart rate, more blood pumped from the heart per minute, and a reduced resistance in the body's smaller blood vessels. Halfway into pregnancy, the heart pumps out 30-50% more blood into the bloodstream compared to pre-pregnancy. Blood pressure drops 5-10 mmHg towards the middle of pregnancy, but then gradually increases until it reaches the pre-pregnancy levels. These circulatory changes create a reserve capacity that is necessary to secure nutritional and oxygen supply both to the mother and the fetus, at rest and during activity.

Circulatory changes associated with the body's position are important for pregnant women both at rest and during exercise. After the first trimester, the uterus / fetus will push against the blood vessels in the abdomen when the mother lies on her back. This hampers blood supply back to the heart, reducing the amount of blood pumped out of the heart. For this reason, pregnant women should avoid lying on their back, both at rest and during exercise. Standing completely still also causes a markedly reduced blood volume to be pumped out of the heart, so this should also be avoided.

It is unclear how the pregnant heart rate responds to smooth submaximal exercise. Both failure and normal response to weight-bearing and non-weight-bearing loads have been reported. This makes it a little difficult to use heart rate as a good measure to regulate intensity of exercise during pregnancy.


Pregnancy leads to major changes in breathing. The amount of air in and out increases by about 50%. This increases the amount of oxygen in the blood - most during the first trimester, and then decreases during the subsequent trimesters until birth. Oxygen uptake in the body also increases. Due to increased oxygen demand at rest and increased breathing work, due to the enlarged uterus pushing up the diaphragm and the lung volume therefore becoming smaller, the amount of oxygen available to a pregnant woman who is exercising is also reduced. The body's maximum capacity is therefore slightly reduced. In some well-trained women, however, the maximum oxygen uptake does not appear to decrease and no changes in the acid-base balance during exercise during pregnancy, as compared to non-pregnant ones, are also observed.

Temperature regulation

Circulation is most affected by the increased metabolic needs (metabolic needs) that exercise brings. Therefore, it is crucial how the body can cope with the excess heat that is formed during exercise. In addition, heat production is increased during pregnancy. The increase in body temperature during exercise is directly linked to the intensity of the exercise. At moderate exercise intensity with aerobic exercise at normal temperature, the base temperature of women who are not pregnant with 1.5 C increases during the first 30 minutes of exercise and then reaches a plateau if exercise continues for another 30 minutes. The body gets rid of the excess heat through increased blood circulation in the skin and sweating. If the heat production exceeds the body's ability to get rid of the heat, for example during heat training, in humid environments or in connection with high-intensity exercise, body temperature will continue to increase. During long workouts, fluid loss can reduce the possibility of sweating, which in turn reduces heat loss and increases body temperature. Maintaining fluid balance and thus blood volume is therefore important for temperature control.

Knowledge about the effect of exercise on body temperature during pregnancy is limited. The fetal temperature is about 1 C higher than the mother's temperature. Animal studies have shown that an increase in the mother's temperature above 1.5 C in the early stages of fetal development can be harmful. Temperatures above 39 C during the first 45-60 days of pregnancy may therefore be harmful in humans as well. However, there are no reports that high temperature in connection with exercise has led to birth defects.

Fetal reaction to exercise

In an uncomplicated pregnancy, the risk of birth defects due to the mother exercising is very small. The vast majority of risks to the fetus are hypothetical. It seems that the birth weight of the child is slightly affected by exercise in women who have a sufficient energy intake. Studies of athletes who continue with relatively hard physical exercise during pregnancy suggest that such activities pose very little risk.

Medical assessment

Follow-up of pregnant women exercising has not been sufficiently done through routine pregnancy checks. If there are no medical conditions that worsen during physical exercise, the pregnant woman should be encouraged to participate in regular physical activities of moderate intensity. Elite athletes who continue with hard training may need closer monitoring.


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