Physiological changes during pregnancy

Normal and Therapeutic Nutrition 3(2+1)
Lesson 9:Maternal Nutrition

Physiological changes during pregnancy

Changes in the mother's body

  • Mother establishes some nutrient reserves to help her later
  • All vital organs in mothers body increases activity
  • All changes are controlled by hormones

Physiological adjustments during pregnancy

  1. Basal metabolism increases by

    5% in 1st trimester
    12- 15 % in 2nd & 3rd trimester

  2. Increase in thyroid function increases the BMR Increase in BMR in the 2nd half of pregnancy averages to 150k cal/ day
  3. Gastric tone is decreased. Therefore nausea and vomiting are common.Gastrointestinal motility diminishes helping in increased absorption of nutrients as the food movement is slow. Absorption of calcium, iron, vitamin B12 etc is increased
  4. Decreased ability to taste salt – A physiologic mechanism for increasing salt intake.
  5. Increased progesterone level relaxes uterine muscle and allows expansion for foetal growth.
  6. Changes in renal function is seen

    GFR (Glomerular filteration rate) is increased and several waste products are cleared very fast. Water is excreted at higher rate in the mid pregnancy and at lower rate in advanced pregnancy

  7. Increased loss of free fatty acids ; decreased loss of calcium and B-complex Vitamins
  8. Blood composition:

    Plasma volume increases by 50% resulting in apparent decreased levels of Haemoglobin.

    Red cell mass increases by 20%

    The concentration of heamoglobin (Hb) and packed cell volume(PCV) falls despite increase in total Hb. This is called as the physiological anemia of pregnancy. Therefore the normal Hb level in pregnancy is 11g/dl.

    Total serum protein decreases

    Serum tocopherol, carotene & cholesterol increase

  9. Water balance

    Total body water increases by almost 7 litres. This places stress on the kidney for disposing excess water.

  10. Hormonal changes:

    Progesterone prepares inner lining of uterus for implantation of fertilized ovum

    Gonadotropins deal with organ formation of foetus till 4th month

    Estrogen levels increase after 3rd month and along with progesterone stimulate the growth of mammary glands

    Steroid hormone levels increase and help in retention of water and sodium

  11. Weight gain in pregnancy:

    It is better to start pregnancy when the women’s BMI is between 20 – 26 because maternal and foetal complications occur at both extremes.

    Majority of women have marked increase in thirst and appetite. Morning sickness may initially counteract this increased appetite

    Consumption of non-food items like laundry starch, ice cubes or clay is called PICA. It is a temporary phenomenon that disappears after pregnancy.

    Normal pregnancy is associated with a weight gain of 11- 13kgs. Indian woman from poor rural areas gain only 5- 7 kgs of additional weight.

Increase in weight is due to

    • Weight of foetus ----- 3,300g
    • Weight of placenta ------ 650g
    • Increased uterine & mammary tissues ----- 450g
    • Water retention decreased extra cellular fluid 1000g, amniotic fluid- 800g
    • Increased blood volume ----- 1250g
    • Fat stores of mother ------ 4000g

    • Most of the weight gain is during second and third trimester

    • 10 weeks ----- 650g
    • 20 weeks ----- 4000g
    • 30 weeks ----- 8500g
    • 40 weeks ----- 12500g
  • Low weight gain leads to delivery of low birth weight baby
  • Less than 50% of normal weight gain is said to be low weight gain. This may be because of excessive heavy work or inadequate calorie intake.
  • Whereas excessive weight gain is increase in additional weight of more than 50% of normal. It may result in excessive fat & fluid accumulation
  • Obesity during pregnancy may lead to certain complications
  • Foetus is likely to be overweight & large. Therefore it becomes difficult for delivery.
  • No dieting is recommended for overweight women in the last weeks of pregnancy.
Last modified: Monday, 24 October 2011, 6:35 AM