Training Considerations During Pregnancy: Part 4 Medical and Physiological Considerations
Medical and physiological considerations during pregnancy include gestational diabetes mellitus which has risks for both the mother and the foetus, the changes that occur in the cardiovascular, respiratory, endocrine, nervous and gastrointestinal systems during pregnancy, and pre-eclampsia which is characterised by hypertension, proteinuria and severe fluid retention.
Gestational Diabetes Mellitus
This involves any degree of intolerance to insulin on the part of the mother that is first recognised during pregnancy. This form of diabetes involves relative resistance to insulin. This form commonly develops when the circulating insulin does not counteract the lowered insulin sensitivity brought on by pregnancy. The causes are not completely understood though there is a belief that it is a survival mechanism for the developing foetus to ensure adequate fuel supply for growth and development. This comes at the expense of the mother’s ability to process glucose.
Thus the mother experiences increased glucose levels in the blood at a time when she has a decreased ability to use this glucose. Those who develop this condition are found to be more likely to have larger babies and have an increased risk of developing Type 2 Diabetes later in life.
Risks to the mother resulting from GDM:
Pre-eclampsia or pregnancy induced hypertension
Urinary tract infections
Macrosomia (large baby) can lead to difficult delivery or C-section
Risks to the foetus resulting from GDM:
Heart defects
Kidney defects
Spinal defects
Respiratory distress syndrome (imperfectly expanded lungs)
Regular exercise in previously sedentary women can help normalise blood glucose levels, which may help hyperglycaemic effect of the insulin de-sensitivity. Using exercise programs that promote the use of large muscle groups with compound movements can help to increase glycogen utilisation by the mother. The mother’s exercise tolerance is increased for various periods depending on insulin and contractile activity thus helping to normalise blood glucose profiles.
High-intensity activities are not advised due to the compounded effect of an increased metabolic rate potentially increasing glycogen usage post exercise. This can lead to potential deficiencies for the child and thus impair development.
The decrease in glucose uptake by the muscles may also lead to fatigue during exercise, which may increase the potential risk of injury to joint structures due to the aforementioned lack of stabilisation of the surrounding musculature.
Exercise is contraindicated for those with Type 1 Diabetes during pregnancy due to associated hypoglycaemia compounding the effects of insulin treatment.
Post-Partum Thyroiditis
This is a condition characterised by inflammation and swelling of the thyroid after giving birth. It causes irregular levels of thyroid hormone production resulting in disruptions in metabolic rate and an increase in the rate at which the mother breaks food down to produce energy. It is a direct result of the increased demand for energy by the foetus for growth and the expectant mothers demands to cope with the rigors of gestation. This increased activity places a large strain on the thyroid gland thus causing it to fatigue and, after birth, decrease production as a result of this fatigue. The effects last no longer than 6 months, however it is difficult to diagnose because symptoms mimic the symptoms of fatigue, depression, and weight change commonly associated with postnatal depression. The two are thus often confused.
The cardiovascular system and pregnancy
Pregnancy causes increased heart rate and oxygen uptake during weight bearing activities. Inactivity can compound the effects of pregnancy and cause further increases in body weight, which can lead to problems such as gestational diabetes and hypertension.
Generally non-weight bearing activities are advised, as they do not place as big a strain on the mother’s joints thus decreasing the risk of excessive force being placed through lax, unstable joints. It must be noted that heart response to exercise varies greatly between individuals and will be affected by many variables including prior exercise experience, pre-pregnancy conditions and genetic factors such as soma type, which will effect muscle specialisation. Thus it is obvious that the trainer must be aware that different bodies respond differently to certain types of exercise.
Pregnancy increases blood volume by 40-50%. However, red blood cell volumes increase by only 18-25% depending on the iron status of the woman. As a result of these decreases in haemoglobin concentrations, the mother’s ability to effectively transport oxygen to working muscles to maintain activity may be compromised. This may magnify the potential feelings of fatigue. At about 32 weeks this effect can result in the development of dilutional anaemia.
This increase in blood volume is also accompanied by increases in cardiac output by as much as 50% as the body attempts to maintain normal blood circulation and cope with the additional volumes of blood. There are large increases in blood flow to the uterus, placenta, kidneys, and skin to ensure adequate nutritional supply to the foetus as well as to deal with the removal of the increased waste produced during gestation and assist thermoregulation to combat the increased heat production caused by increased metabolic rates.
Stroke volumes rise by week 8 and continue to rise to maximum levels during the second trimester.
The Endocrine System and Pregnancy
Increases in insulin can cause possible magnified hypoglycemic responses during pregnancy. This is especially true late in the pregnancy. This increase in insulin increases the risk of gestational diabetes as well as affecting the mother’s ability to produce energy for working muscles.
The placenta secretes Human Placental Lactogen (HPL), which works with oestrogen and progesterone to prepare breasts for lactation. However, HPL also causes glucose sparing. This results in the metabolism of fatty acids thus compounding the effects of insulin sensitivity and increasing the risk of ketone production. This has the potential to increase the risk of hypertension development and renal dysfunction.
During the pregnancy, there are increases in vitamin D levels and the plasma levels of parathyroid hormones. This causes a positive balance during pregnancy. This assists in the mineralisation of bone for the foetus. It is essential that the mother take adequate levels of calcium at this stage or she risks the foetus stripping calcium from her skeleton to ensure adequate development.
Fat accumulation ceases during the second half of pregnancy due to cortisol, growth hormone and insulin continuing to rise along with the growing energy demands of the foetus.
It is important that increasing levels of relaxin are kept in mind at all times. These levels will peak between the eighteenth and twenty-second weeks. The higher level of relaxin will affect ligament laxity and which will continue throughout pregnancy until labour. It is important to note that ligament laxity can remain for as long as six months after birth with pubis symphysis instability occurring up to 8 weeks after birth. As a result, heavy loading lower body exercise and excessive high-intensity weight bearing exercise should be avoided until after this point.
The respiratory system and pregnancy
During pregnancy oestrogen causes the nasal mucosa to become oedematous and congested potentially causing stiffness and bleeding. This can lead to the potential for increased nosebleeds under strain.
There is an increased ventilatory response during rest and sub maximal exercise, particularly in the later stages of pregnancy. This is possibly due to maternal hyperventilation, which can be attributed to progesterone and CO2 sensitivity. This sensitivity occurs to maintain respiratory responsiveness.
A numbing of the autonomic nervous system may also occur and lead to poor intercostal muscle activation. This can be exacerbated by high-intensity cardiovascular activity. The mother may also complain of shortness of breath during the later stages of pregnancy due to restriction of her diaphragm by the growing foetus.
The gastroinstestinal system and pregnancy
The expectant mother may experience nausea and vomiting due to increases in her hormone level. This can decrease the kilojoules available and affect the nutritional status of both the foetus and mother. It can also affect the energy available to the mother for activity.
The expectant mother may also experience heartburn and constipation due to the slowing down of peristalsis.
The Nervous System and Pregnancy
Pregnancy can cause mood changes, increased anxiety, amnesia which can all impact on the mother’s mental well-being. It may also cause a slight decrease in cognitive ability, which may lead to increased risk of falls during complex movements.
Thermoregulation and pregnancy
Normal core temperature sits at about 36 degrees Celsius. However, the expectant mother’s temperature will normally sit higher by about 0.5 degrees.
This is due in part to increased metabolic rates from foetal growth. The foetus produces heat as a result of metabolic activity but it does not have the ability to dissipate this heat. Heat is therefore transferred to the mother.
This gradient may also reverse and the heat produced by the mother may be transferred directly to the child. It is, therefore, essential that a pregnant woman avoid overly hot and/or humid environments and not overly exert herself during exercise. Maintaining adequate hydration levels is vital for thermoregulation and can help ensure this does not occur.
Pre-Eclampsia
This is characterised by hypertension, proteinuria, and severe fluid retention.
Genetic factors and the functions of the placenta play a major role in its development. It is also closely related to insulin resistance and associated conditions such as gestational diabetes, polycystic ovary syndrome and obesity.
Pre-eclampsia can develop at any stage during the second half of pregnancy and can potentially involve all maternal organs. In severe cases it may progress to seizures known as eclampsia, which are linked to high blood pressure. It has the potential to lead to kidney or liver failure, clotting problems and death.
Adequate nutrition is particularly important in the prevention and management of pre-eclampsia.
The mother is particularly at risk if she has any of the following:
It is her first pregnancy
She has pre-existing high blood pressure or other forms of vascular disease
She has a family history of pre-eclampsia or eclampsia
She is a diabetic
There are multiple foetuses involved.
Pre-eclampsia can have several effects on the on the unborn child:
A sluggish blood flow as a result of the hypertension and increased blood volume means the baby can become starved of oxygen and nutrients, which may result in premature birth.
In severe cases the mother may experience vaginal bleeding and abdominal pain as a result of the placenta separating from the uterine wall. This can result in the death of the child if not treated fast enough.
The trainer should be on the look out for the following signs and symptoms:
dizziness
headaches
visual disturbance such as seeing flashing lights
abdominal pain just below the ribs
nausea and vomiting