Maternal Physiological Changes during Pregnancy

Maternal physiological changes during pregnancy

During pregnancy there are progressive anatomical and physiological changes, not only confined to the genital organs but also to all systems of the body. This principally is a phenomenon of maternal adaptation to the increasing demands of the growing fetus.

Reproductive organs:

·   Vulva: Vulva becomes hyperaemic. Labia minora are hyper pigmented and hypertrophied.

·  Vagina: Vaginal walls become hypertrophied and more vascular. Increased blood supply gives the bluish discolouration of the mucosa. The vaginal secretions become copious, thin and white.

·   Uterus: There is enormous growth of the uterus during pregnancy. The uterus in non-pregnant state weighs about 60 gm and measures about 7.5 x 5 x 2.5 cm in size. At term, it weighs 900-1000gm and measures 35 x 22 x 13 cm in size. The changes occur in all the parts of the uterus that is the body, isthmus and cervix.

·  Body of the uterus: There is an increase in growth and enlargement of the body of the uterus. The muscle fibres undergo both hypertrophy and hyperplasia [both increase in length and breath and addition of new muscle fibres.] The uterus feels soft and elastic in contrast to firm feel of the nongravid uterus.

· Decidua: Decidua is the name given to the endometrium during pregnancy. It becomes thick and spongy and blood supply is also increased. The upper and lower uterine segments are formed towards the later weeks of pregnancy. The shape of the uterus changes from pear shaped to ovoid. Uterus rises out of the pelvic cavity by 12th week of pregnancy.

·  Cervix: Cervix softens and loosens in preparation for labour and delivery. There is hypertrophy and hyperplasia of the elastic and connective tissues. Mucous production increases and forms a thick plug (called operculum) effectively sealing the cervical canal to prevent ascending infection from the vaginal canals.

·  Ovary: Both the ovarian and uterine cycles of the normal menstruation remains suspended. Hence no ovulation takes place. Corpus luteum persists in early pregnancy until the development of placenta is completed.

·   Fallopian tubes: They get enlarged as uterus rises in pelvic and abdominal cavities.

·  Breasts: Marked hypertrophy and proliferation of ducts and alveoli occurs that increase the size of the breasts. Blood supply is increased. The nipples become larger, erectile and deeply pigmented. The sebaceous glands become hypertrophied and are called as “montgomery’s tubercles”.

Changes in cardiovascular system.

Blood volume expands as much as 50% to meet the requirements of new tissues and the increasing needs of all systems. Blood vessels are dilated due to the action of progesterone, which predisposes the woman to varicose veins and hemorrhoids (caused by abnormal dilation of blood vessels). The plasma volume increases 40% and the red blood cells increases only 20% that leads to haemodilution, which causes physiological anemia in healthy women. The heart rate is slightly increased to improve blood flow to the fetus and placenta.

Changes in the respiratory system:

As the uterus grow, it presses on the diaphragm and causes shallow and more frequent respiration. Hence respiratory rate is slightly increased and oxygen consumption is increased by 15%.

Changes in digestive system:

Nausea and vomiting occur in the morning usually in early pregnancy. Heart burn and mild indigestion may occur. Constipation may occur probably due to the action of progesterone.

Increased salivation occurs-called as ptyalism. Cravings or desires to nonnutritive substances may occur. After that condition is called as pica. Bleeding gums and tooth loss due to

demineralisation are common.

Changes in the skin:

There is an increased pigmentation occurring around the nipples and areola of the breasts, the center line of abdomen (linea nigra), in the face especially on forehead and cheek (chloasma). Stretch marks (striae gravidarum) occur in abdomen, thighs and breasts.

Changes in skeletal system:

Alternations in posture, walking and gait occur due to change in center of gravity as the uterus enlarges in size. Joint mobility is increased as a result of action of relaxin, an ovarian hormone on connective tissue. Backache is common. Occasional calf muscle cramps may occur due to calcium deficiency.

Changes in urinary system:

Frequency of urination is common in early pregnancy as the gravid uterus pressing on the bladder when it is in the pelvic cavity. Again frequency increases in the last few weeks of

pregnancy due to pressure from the enlarged uterus. When the fetal head enters into the pelvic cavity, lightening will occur. The pregnant woman will have easy breathing as the pressure on the diaphragm is relieved.

Weight gain in pregnancy:

The total weight gain during pregnancy averages 10 to 12 kg. The total weight gain is distributed approximately as follows:

Weight gain

Upto 20 weeks - 2 kg.

After 20 weeks till term – 10 to 12 kg

Distribution of weight gain during pregnancy

Foetus    3.4 kg

Placenta 0.6 kg

Amniotic fluid 0.6 kg

Fat deposit and protein 3.5 kg

Uterus 0.9 kg

Breasts 0.5 kg

Increase in blood volume 1.5 kg

Increase in extra cellular fluid 1.0 kg

Total weight gain 12.0 kg

Periodic and regular weight checking is of high importance to detect abnormality.

Changes in endocrine system.

Corticosteroid production is increased. The anterior pituitary gland is enlarged. Adreno corticotrophic hormone, melanocyte stimulating hormone and thyrotrophic hormone increase their activities.

Diagnosis of pregnancy:

The placenta produces a hormone, called human chorionic gonadotrophin, which is excreted in the urine. This hormone is usually detected in the urine within a week of the first missed period. Biological and immunological tests depend on the detection of human chorionic gonadotrophin in the urine.

Immunological test:

Immunological pregnancy test depends on the fact that human chorionic gonadotrophin has antigenic properties. The test consists of two steps.

- HCG antiserum is added to urine of the woman.

- Sensitized red cells or latex particles are then added.

The first step neutralizes HCG antibodies; hence no agglutination occurs after the second step, confirming pregnancy.