2.4 Physiological and Anatomical changes associated with pregnancy
Pregnancy is associated with normal physiological changes that assist fetal survival as well as preparation for labour. Many of these changes are regarded as signs and symptoms of pregnancy. The changes are not confined to the reproductive organs alone, every tissue and organ react to stimulus of pregnancy and the metabolic, chemical and endocrine balance of the body is also altered.
Changes in Reproductive system:
Uterus: changes occur in the size, it enlarges to give nourishment and protection to the growing fetus. It also has the responsibility of expelling the fetus at a viable age, so the muscles coat develop in a remarkable degree.
Weight – from 60gm to 900-1000gm.
Size – from 7.5cm to 35cm (height) 5cm to 23cm(width), 2.5cm to 20cm (thickness) (7.5 x 5 x 2.5 to 35 x 23 x 20)
Shape – from pear shaped to globular
Layers of the uterus -
a). Endometrium – becomes deciduas which is more thicker, richer and vascular at the fundus and upper body of the uterus due to the effect of progesterone and oestrogen produced by the corpus luteum. These areas are the usual site for implantation, thus the decidua is less vascular and thinner in the lower uterine segment.
b). Myometrium – it consist of bundles of smooth muscle fibres held together by connective tissue. In pregnancy the muscles fibre grow up to 15-20 times more than the non-gravid length. The increase in size and number of the uterine muscle fibre (hypertrophy and hyperplasia) is due to the effect of oestrogen.
A slight irregular painless contraction starts from the first trimester, known as Braxton Hicks contraction which facilitates the formation of the lower uterine segment. Although progesterone suppresses myometrial activity throughout most of the pregnancy, by the 36th weeks, the contractions increases which eventually leads to ripening of the cervix and labour.
Cervix:
The cervical cells secretes thick and viscous mucus which forms a cervical plug called the opeculumthat provides protection against infection by occluding the os. The cervix looks bluish due to increased vascularity.
The cervix contains more fibrous tissue and less muscle when compared to the body of uterus that is why it remains firmly closed and resist pressure from above when the mother is in upright position.
The cervix softens (ripens) in late pregnancy due to the action of prostaglandins. Effacement occurs in the primigravida during the last 2 weeks of pregnancy, but it usually occurs when labour begins in the multigravida.
Vagina:
There is hypertrophy and the capacity of the vagina increases.
Changes in the connective tissue make it more elastic.
The increased blood supply leads to bluish discoloration and
There is usually a marked increase in the normal whitish vaginal discharge known as leucorrhoea.
Breast:
There is weight increase of about 450g,
The nipples become darker and erectile.
Primary areola and Montgomery’s tubercles appears (about 12-30 small nodules).
Changes in the cardiovascular system
Heart:
The workload of the heart increases during pregnancy and the muscles hypertrophies leading to the enlargement of the heart. The gravid uterus pushes the diaphragm which in turn pushes the heart upward.
The heart rate increases and the amount of blood pumped by the heart also increase resulting in a raised cardiac output. The heart rate increase by about 15 beats per minute’s i.e. from 70 to about 85 beats per minutes.
Although the cardiac output increases, the blood pressure does not due to the effect of progesterone on smooth muscles, causing the arterial walls to relax and dilate.
There’s more increase blood flow to the uterus, kidneys, breast and skin.
Blood:
There is increase in the blood volume of about 20-100% depending on the body size, parity, and no of fetus she is carrying.
The increase in plasma level is greater than the increase in Red blood cells; this is referred to as Haemodilution.
It is characterized by low haemoglobin level of around 11-12 g/dl or pcv of 29% and the effect is known as Physiological anaemia.
Changes in the respiratory system
The effect of pregnancy is minimal.
The lungs are displaced slightly upward when the uterus encroaches the thorax.
There is an increase of about 20% in the O2 consumption rate due to increase metabolic need of the mother and fetus.
The shape of the chest changes and the circumference increase, and may not recover their original position after pregnancy.
Changes in the urinary system
Due to the influence of progesterone the ureters become relaxed and dilated, they become elongated and curved around the brim of the pelvis.
It usually results to statics of urine in the ureters which results to bacteriuria and infection of the urinary system.
Due to reduction in the capacity of the bladder in early and late pregnancy, the pregnant women constantly pass urine.
Changes in the gastrointestinal system
There is increased salivation due to inability to swallow the saliva as a result of nausea in some women.
The gums are oedematoes and soft due to the effect of oestrogen. Nausea and vomiting is common.
A craving for certain food can develop or an increase in appetite in some women, also a change in the sense of taste can occur.
The growing uterus displays the stomach and intestines.
The cardiac sphincter becomes relaxed leading to the reflux of acid to the oesophagus which results to heartburn.
Gastric tone, peristalsis and HCL secretion reduces and gastric emptying time is decreased.
The delay in the movement of food through the intestines leads to increased absorption of water, thereby predisposing the pregnant woman to constipation.
Obstruction of the intestine by the uterus and the effect of progesterone on smooth muscles can also causes constipation.
Changes in maternal weight
Weight gain during pregnancy is indicative of maternal adaptation and fetal growth. The following is the expected weight gain;
4kg in the 1st 20wks
8.5kg in the 2nd 20wks (0.4kg/week)
Approximately 12.5kg total.
Fetus- 3.4kg
Placenta- 0.6kg
Amniotic fluid – 0.8kg
Increase in weight of uterus – 0.4kg
Increase in weight of blood volume - 1.5kg
Extracellular fluid – 1.4kg
Fat- 3.5kg
Changes in the skin
The skin stretches on the abdomen to accommodate the uterus and extra fat deposit thus tears occurs in deeper layers of the skin;
Striae gravidarum: scars from the tears are seen as irregular marks called striae gravidarum. Similar scars may occur on breasts and thighs. They are more marked when there is excessive stretching like in multiple pregnancy.
Chloasma: or mark of pregnancy – it is a skin pigmentation which occurs on the face. It is not common in African women.
Lineanigra: it is the line extending from the pubis to the xiphisternum which has become darker.
Changes in Muscular Skeletal system
The hormone relaxin which is secreted towards the end of pregnancy softens the soft tissue structures of the pelvis, e.g ligaments, cartilage in between joints (Symphysis pubis, sacroilliac joints, pelvic floor muscles, etc.