Pregnancy changes a lot of things and brings about so many effects in the woman emotionally, psychologically, socially, economically and physically. The physical changes are noticed in the woman’s body and body functions as an effect of pregnancy. The physiological response of the woman to pregnancy covers about every systemic function in her body which can not be regarded as pathological because they usually disappear after the pregnancy period when she must have successfully put to bed.
MATERNAL PHYSIOLOGICAL CHANGES DURING PREGNANCY
Metabolic changes which is accompanied by fetal growth result in an increase in weight of around 25% of the non pregnant weight during pregnancy, approximately 12.5kg in the average woman. The main weight increase occurs in the second trimester of pregnancy and is usually around 0.5kg per week. Towards the end of the pregnancy, the rate of weight gain diminishes and weight may fall after 40th week. Weight increase during pregnancy is a combined result of fetal growth, enlargement of maternal organs, maternal storage of fats and proteins, and increase in maternal blood volume and interstitial fluid.
Pregnancy affects how the woman metabolises and utilises the food she consumes especially carbohydrates, proteins and fats.
- There is a noticeable change in blood glucose , where blood glucose levels after a meal remains high to facilitate placental transfer which is the reason for the phenomenon called gestational diabetes. The reason for the high glucose levels is because of the high demand of the fetus to obtain an easily convertible source of energy, aggravated by the need to store up energy for future demands such as lactation and the steadily increasing growth of the pregnancy.
- There is an average of 20% increase in dietary intake of protein during pregnancy. Half of the protein diets are metabolised for maternal use and the remaining half for the fetus and placenta.
- Fat metabolism also changes during pregnancy. Fat is the major form of stored energy during pregnancy and most of it is kept in the form of depot fat in the abdominal wall, back, thighs and a modest amount is stored in the breast.
Physical changes in the respiratory system begin early in pregnancy and are responsible for the improvement in gaseous exchange. Respiratory rate is unchanged and the elevation of the diaphragm decreases the volume of lungs at rest. The tidal volume is increased by up to 40% leading to an increase in the minute ventilation from 7.25litres to 10.5litres. Due to the pulmonary hyperventilation, the concentration of carbondioxide in maternal plasma is reduced by around 8% compared with non pregnant women.
- Cardiac output increases dramatically in pregnancy from 4.5litres per minute to 6.0litres per minute. This increase is seen greatest in the first trimester and reaches its peak in the 24th week and is due to an increase in both heart rate and stroke volume.
- Heart rate increases from an average of 70 beats per minute to an average of 78 beats per minute at 20 weeks gestation and up to a peak average of 85 beats per minute in late pregnancy.
- Stroke volume increases from 64ml to 70ml in mid pregnancy.
- Blood volume and blood pressure increases during pregnancy to increase organ perfusion in pregnancy. Renal blood flow increases by 35% and uterine blood flow by up to 250%.
- During pregnancy, intracellular water is unchanged but both blood and interstitial fluid are increased. Plasma volume increases at a greater rate than the red cell mass and protein levels which results in reduced blood viscosity.
- Increased venous pressure produces varicosities and edema of the vulva and legs which are most visible during the day time due to upright posture but less at night when the woman lay in bed.
- Haematological values changes due to increased pregnancy demands. There is reduction in red cell count from 4.5 million per ml to around 3.8 million per ml. Haematocrit level falls during pregnancy and so does haemoglobin levels. Leukocytes (white blood cells) increases while platelets levels decline progressively throughout pregnancy. Pregnancy produces hypercoagulabilty with increase in fibrinogen and factors VII to X.
- Relaxation of smooth muscles due to high progesterone levels during pregnancy results in the relaxation of gastric sphincter causing heartburns from gastric regurgitation.
- There is also slight reduction in gastric secretion and gastric motility resulting in slow gastric emptying which can cause nausea.
- Reduced motility in small intestines which increases time for absorption.
- Reduces motility of the large intestine increases time reabsorbtion and induces constipation.
- Growth of fetus also tends to increase appetite and thirst.
- Frequency of micturition in early pregnancy and at term pregnancy due to changes in pelvic anatomy.
- Hydronephrosis and hydro-ureters occurs due to increased vesico-ureteric reflux from loss of smooth muscle tone due to high progesterone levels. This gets better at the latter parts of pregnancy.
- Urinary output is slightly diminished.
- There is an increase in tubular reabsorbtion of water and electrolytes.
- Glomerular filtration rate increases which accounts for glucosuria (high glucose in urine).
Reproductive system changes
- Breasts increase in size due to proliferation of the glands and ducts under the influence of high estrogen and progesterone levels during pregnancy. The secretion of colostrum may begin in the first trimester and continues till term.
- The body of the uterus grows by hyperplasia and hypertrophy of the muscle fibres. The weight of the uterus increases from 50g (when not pregnant) to about 1000g.
- The cervix softens due to increased vascularity. There is an increased secretion of mucus from the cervical glands which becomes thickened thus forming the protective plug called operculum in the cervical os.
- Vaginal and pelvic changes also occur. Increased vascularity, muscular hypertrophy and softening of connective tissues are seen which allows for the distention of the vagina and pelvis during birth.
- Progesterone increases and reaches a maximum of 250mg per day.
- Estrogen levels increase up to a thousand fold due to placental production of the hormone in addition to the fetal adrenals.
- Aldosterone is much increased promoting water and sodium retention.
- Plasma renin is 5 – 10 times more during pregnancy. This also accounts for the increase in angiotensinogen and angiotensin levels.
- Human chorionic gonadotropin (hCG) levels increase and reach its peak levels in the first trimester.
- Pituitary hormones like follicle stimulating hormone (FSH) and Luteinizing Hormone (LH) are suppressed during pregnancy but prolactin levels are high throughout pregnancy.
Kelvin P. Hanretty : “maternal physiology” Obstetrics and Gynaecology Illustrated (sixth edition).