PHYSIOLOGICAL CHANGES IN PREGNANCY
Foetal development is accompanied by many physiological, biochemical and hormonal changes which influence the nutrient needs and the efficiency with which the body utilizes them. The changes include
1. Increased Basal Metabolic Rate (BMR)
Due to foetal growth the BMR increases by about 5 percent in the 1st trimester reaching a high level of 12 percent during later stages of pregnancy.
2. Gastro intestinal changes:
Gastro intestinal motility diminishes which may result in constipation. The acid and pepsin secretion in the stomach is less and additionally a relaxed lower oesophagal sphincter may cause regurgitation of stomach contents into the oesophagus leading to sensation of heartburn and vomiting. This becomes more pronounced with increasing pressure of the foetus.
In later half of pregnancy the efficiency of absorption of iron, calcium and B vitamins increases as a natural adaptation mechanism to meet the increased needs.
3. Hormonal changes:
During pregnancy there is increased secretion of the following hormones.
Aldosterone by the adrenal gland.
Progesterone which relaxes uterine muscles to expand to accommodate the growing foetus.
4. Changes in body fluid
The blood volume expands by 50 percent and this increased amount of blood is required to carry nutrients to the foetus and remove metabolic wastes from the foetus.
With increase in blood volume the concentration of plasma proteins, haemoglobin, blood glucose and water soluble vitamins decrease. The decline in serum albumin level tends to accumulate extra cellular water during pregnancy.
Haemoglobin level drops to 11g / 100ml (normal range 12-13 g / 100 ml) despite an increase in total haemoglobin content ie., haemodilution occurs. Thus during pregnancy, women with haemoglobin levels less than 10 g / 100 ml are considered anaemic.
5. Altered renal function
Increased blood volume and increased production of waste products like creatinine, urea and other wastes due to foetal and maternal metabolism produces a high Glomerular Filtration Rate (GFR) and the renal tubules are unable to adjust completely to this load. Some percentage of nutrients which are normally completely reabsorbed are excreted. Compounds like glucose , aminoacids and water soluble vitamins may appear in trace amounts in urine.