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Chapter: Maternal and Child Health Nursing : Physiology of Pregnancy

Physiological changes due to pregnancy

As soon as a woman gets pregnant, there is a dramatic physiological adaptation to pregnancy in various systems of the body especially in the reproductive system so that her body can cope with added work and nurture the fetus and prepare for labour and lactation.

Physiological changes due to pregnancy


As soon as a woman gets pregnant, there is a dramatic physiological adaptation to pregnancy in various systems of the body especially in the reproductive system so that her body can cope with added work and nurture the fetus and prepare for labour and lactation.


This changes is sometimes under estimated but the effects vary from one woman to another. Midwife’s understanding of the physiological changes will enable her to identify deviation from normal and will be able to provide adequate care to the woman or take appropriate stop to solve her problems.


Changes in the uterus


After conception the uterus provides a nutritive and protected environment for the fetus to grow and develop.


Size: The size increases progressively so that at term it is from7.5 x 5 x 2.5cm to 30 x 23 x 20cm.


The Weight: From about 60gm to 90gm.


The position: changes from pelvic organ to abdominalorgan. By the 12th weeks of pregnancy it is no longer anteverted and anterflexed but become more vertical and


leans towards the right as pregnancy progresses.


Shape – As it fills up with the growing fetus the uterus becomesmore globular. It changes from the ovoid shape when it was in the pelvic cavity to become globula.


The Decidua: becomes more thicker and increased vascularity ofthe lining. This is more marked in the fundus and the upper body of the uterus. The deciduas and trophoblast produce relaxin which relaxes the myometriam relaxation and play a role in ripening of the cervix at term and rupture of the membranes.


Myometrum: Each muscle fibre increases to about ten times its length and at least three times its width due to hyperplasia and hypertrophy of the myometrial cells under the influence of oestogen.


Blood supply – increases to almost ten times due to increasedcardiac output from about 50mls/min to 450 -700ml/min at term. Eighty percent of the blood flows through the placenta there is enlargement of the blood vessels and give rise to a sound known as uterine “soufflé”.


Support – the greatest strain is on the round ligament the changesin the size vary with each woman and the gestational age.


Changes in the uterine size


The uterus grows at such a regular rate that it is possible to estimate period of gestation by size. There is of course room for error as uterus may contain more than one fetus, large baby or excessive amount of amniotic fluid. Before 12th weeks the uterus remains a pelvic organ and maintains the ovoid –sha pe.


12th Week –The uterus fills the pelvic cavity and fundus just reaches the summit of the symphysis pubis. It is globular in shape about the size of a grape fruit. It is more upright usually incline to the right.


16th Week – the uterus has risen to less than halfway between thesymphysis pubis and the umbilicus or about 7.5cm above the symphysis pubis. The shape is more ovoid than global because it is in contact with the abdominal wall quickening is felt. Uterine soufflé can be heard. The isthmus andthe cervix develop into the lower uterine segment.


20th Week – the fundus is about the level of the umbilicus. Fromthis stage the uterus become more ovoid in shape. Positive signs of pregnancy can be elicited without ultrasound (fetal heart, fetal parts and fetal movement.


24th Week – Fundus is at the upper margin of the umbilicus 20cm.the uterus tends to lean and rotates on its axis towards the right.


30th Week –The fundus can be palpated midway between the umbilicus and xiphisternum. The assessment may be subjective as the level of umbilicus may vary in size.


36th Week – The fundus rises to the highest level, in contact withthe xiphisternum. No finger breadth between the xiphisternum and the fundus.


38th Week –The lower uterine segment is formed. The fetal presenting part descends and the fundal height drops, this is known as lightening, leaving pressure on upper abdomen engagement may occur in some women.


40th Week - The uterus is ready to go into labour. The loweruterine segment is relaxed and stretched the cervix is effaced and soft. The fetus further sinks down into the lower segment and the fundal height drop to about 34 week when the head is engaged.


The CervixDuring pregnancy the cervix remain closed.Blood supply is increased that it becomes softer and more bluish in colour. The cervical glands secrete more mucus. A plug of this viscous mucoid material fills the cervical canal. It is known as operculum. It minimizes the risk of ascending infection into the uterus. Collagenase and protoglandin are involved in cervical ripening. Theoretically effacement takes place about 2 week before term in primigravidae and when labour begins in multigravidae.


The vagina: there is some degree of hypertrophy of themuscle layer of the vagina causing the epithelium to become thicker. Increase blood supply (hyperaemia) result in the blue discoloration and increase pulsation at the fornix. The Doderlein bacilli act upon the vaginal collegen resulting in lactic acid which increases pH of Vaginal secretion to 4.5 – 5.0. Thi s increases vaginal secretion – ( Leuchorrhoea) during pregnanc y.


The Fallopian Tubes and the Ovaries:


Blood supply to these organs increases. They become more vertical in position as the growing uterus fills the abdominal cavity. The corpus luteum enlarges, producing high level of oestrogen and progesterone in the first 10-12 weeks. Corpus inturm degenerates after the 12th week and placenta take over its function.


The Breast: Owing to increase blood supply and the effectof oestrogen and progesterone new duct and actini cells are formed. The breast increases in size. There is tingling sensation in early pregnancy, the breast is more firm and tender. The nipple becomes more dark and prominent. The primary areola becomes darker at the 12th week. Dilated veins may be open on the chest and breasts. Clear fluid may be expressed. At 16th week colestrum may be expressed, and secondary areola is formed around the primary areola .


From the 8th week montgomany’s tubercles are formed in the areola. They secret sebum to keep the nipples soft and pliable.


Cardiovacular system: Profund changes take place incordiovasular system during pregnancy. The heart slightly enlarges to about 12% to meet the challenges of increase blood volume – the blood volume increases by 50% plasma volume in the mid trimester (hydraemia) being mainly water volume. This leads to what is known as physiological anaemia. Blood vessels are dilated due to action of progesterone and this predisposes to varicose veins and haemorrhoids. Cardiac output increases.


Blood pressure - Even with raised cardiac output arterial blood pressure is reduced by 10%. Early pregnancy is associated with decreased diastolic blood pressure but little change in systolic by mid trimester the blood pressure slightly increases 5 -10mm/g in systolic and 10-15mm/mg in diastolic but soon return to normal before term.


Posture can affect blood pressure – supine position can decrease cardiac out put by as much as 25%.There is increase production of red blood cell to meet the needs of the mother and baby .Despite this there is decrease haemoglobin concentration because of increase plasma volume.


Respiratory system


The Basal Metabolic Rate (BMR) is increased during pregnancy. Increased cardiac output leads to increase in tidal volume that enters and leaves the lungs during normal respiration. The rising uterine fundus compresses the base of the lungs making respiration to become costal. Up to 70% of pregnant women experience dyspnoea beginning from first or second trimester. Cardiac and pulmonary disease must be ruled out.


Digestive system


The gum becomes oedematous, soft and spongy. It is easily brushed. Sometimes gingivitis (epulis) may develop.


Nausea and morning sickness occurs during the first three months of pregnancy in about 50% pregnant women.


Pregnancy hormone – Progesterone affect all smooth muscles of the gut resulting in indigestion, heart burn and constipation.


Skin changes: Intergumentary


From the third month until term, some degree of skin darkening is observed in about 90% of pregnant women. The abdominal skin stretches to accommodate the enlarging uterus and extra fat deposit resulting in small tears in the deeper layers of the skin. These are the stretch mark on the abdomen known as triae gravidarum. It may also occur in the breasts, thigh and back of the legs. More marked in multiple pregnancies and polyhydranios.


Pigmentation of the skin occurs on the face – norma lly referred to as chloasma or pregnancy mask. The mid lime seen to be extending from xiphistermum to the symphysis pubis area become darker and more pronounced. It disappears few days after delivery. It is known as linea nigra.


Skeletal system


There is alteration in the gait of the woman in an attempt to maintain balance due to the weight of the growing uterus. There is increase movement in the joints due to relaxing effect of the pregnancy hormones on the ligament.


Nervous system


Emotional instability is common in pregnancy and the woman cries easily. There is increase tendency to anxiety, fear and even depression.


Weight Increase in Pregnancy


A steady and adequate weight gain is necessary for the health and well being of the woman and the fetus. An average maximum weight gain of 11.5kg is expected during pregnancy. During the 1st trimester a weight gain is slow most weight gain occurs in the second and third trimesters. It results from increase muscle tissue and fat, especially the breast, buttocks and loins and thighs. Growth of the uterus and the product of conception, fluid retention increase blood volume. Increase of 20% of the non gravid uterus is considered normal. The first 20 weeks the average weight gain is 2kg, weight gain is rapid during the second 20 week, a gain of 0.5kg per week making a total of 11 -12kg. Any weight above this should be investigated.


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