Physiological changes in Pregnancy


Baby is entirely dependent for its nourishment on mother. To ensure the proper growth and development of the baby and safeguard the health of both, mother and baby, many physiological changes happen in mother’s body. Some of these changes continue to happen throughout the period of pregnancy, while some are limited to specific trimester.

Some of these sudden changes may adversely affect the quality of life and may mimic as disease symptoms. There exists a very fine line of demarcation between the upper limit of physiological changes and early signs of disease/ complications. The awareness towards normal changes in pregnancy and warning signs may help us to diagnose any deviation from normal and undertake intervention well in time to protect both mother and baby.


The average weight gain in singleton pregnancy is around 11-16 kg and in twin gestation it is around 15-20 kg.



In the first trimester there is usually around 1 kg weight gain. However, some mothers may lose little weight in first trimester due to increased metabolism. In the second and third trimester there is approximately 5 kg gain in each. Therefore average 11 kg weight gain in entire duration of pregnancy.

Digestive System:


  • Nausea:

This is one of the most common problems in first trimester. The progesterone hormone not only stimulates the vomiting center in brain, but also relaxes the Gastro-esophageal sphincter resulting in reflux of stomach contents.

Nature has probably designed the nausea and vomiting in first trimester of pregnancy as a protective mechanism to safeguard the baby from accidental ingestion of harmful substances during the period of organ development.

Excessive vomiting resulting in approximately more than 5 % weight loss, decreased urine output less than 400 cc in 24 hours and electrolyte imbalance is referred as Hyperemesis Gravidarum and needs immediate intervention.

The simple remedies to control nausea and vomiting are discussed in section on common problems in pregnancy.

  • Diet & Appetite:


The pregnant mother requires additional 300 kcal of energy per day. Therefore mother should increase her food intake. She should preferably consume easily digestible food rich in nutrition, proteins and minerals.

  • Early satiety:

In the third trimester, as the size of gravid uterus increases, it displaces the intestines and stomach upward and causes compression pressure on them. This results in early satiety with little meal, but frequent hunger.

  • Bleeding at gums or vomiting:

In pregnancy, there is increased blood flow to all the organs of the body. This may result in bleeding from gums, nose or in vomiting even with trivial trauma.

  • Hyperacidity & Heart burn:

The progesterone hormone relaxes the gastro-esophageal sphincter. Also, the progressive growth of gravid uterus displaces the intestines upward resulting in reflux. Hence, the pregnant mothers are more prone for hyperacidity and heart burn.

  • Constipation:

The progesterone hormone relaxes the smooth muscles of small intestines and reduces the peristalsis resulting in slow bowel movement and hence constipation.

  • Hemorrhoids:

The higher incidence of constipation and increased intra-abdominal pressure due to gravid uterus on the perineum predisposes to the risk of hemorrhoids in pregnancy as it advances.

  • Jaundice & Gall bladder stones:

The progesterone hormone also relaxes the smooth muscles of biliary system resulting in accumulation of bile products in liver and gall bladder predisposing to the risk of cholestasis (Jaundice) or gall stones respectively.

  • Recurrent oral infections:

The changes in pH of oral secretions, low immunity associated with pregnancy and gastro-esophageal reflux results in dental caries and recurrent oral infections.

Oral infections may increase the risk of preterm delivery.

Recommended life style modifications to handle these problems have been discussed in respective sections of common problems.

Urinary system:


  • In pregnancy, the blood circulation to kidney increases resulting in higher glomerular filtration rate efficiently clearing waste. As a result, the concentration of urea and creatinine in blood is lower than in non-pregnant state. The nature has designed it so that the waste products transports from fetus to mother following principles of diffusion (from higher fetal concentration to lower maternal concentration).
  • The concentration of sodium in mother’s blood increases under the influence of hormones, so that mother’s blood retains the water to facilitate hemodilution of pregnancy to permit easy flow of blood to baby.
  • The progesterone hormone also relaxes the smooth muscles of urinary system, resulting in urine stasis, predisposing to recurrent urinary infections or stone formation.
  • In the first and third trimester, the urinary bladder gets compressed between the gravid uterus and symphysis pubis bone leading to increased urinary sensation and frequency.
  • The increased intra-abdominal pressure due to gravid uterus predisposes to pelvic organ prolapse and urinary leakage on laugh, cough or bending forward.
  • The lower immunity in pregnancy along with persistent perineal moisture due to increased vaginal secretions and failure to wipe the perineum dry after urination predisposes to recurrent vaginal and urinary infections, that adversely may lead to miscarriage or premature delivery.

Finer details of perineal hygiene are discussed in the segment of ‘white discharge in Pregnancy’.

Respiratory System:


The oxygen demand in pregnancy increases to ensure the optimum growth and development of fetus and to meet out the increased metabolic demands of pregnant mother.

As a result, the respiratory system has to work more to ensure the adequate supply of oxygen and take away the waste carbon dioxide gas. So, both the rate and intensity of respiration increases in pregnancy.

However, as the pregnancy advances, the gravid uterus displaces the intestines upwards subsequently displacing the diaphragm and reducing the lung capacity, thereby causing shortness of breath.

The increased blood supply to inner lining of nostrils, respiratory tract and lungs can lead to congestion resulting in breathlessness and increased respiratory efforts and occasional bleeding from nose on forceful sneezing.

Due to changes in hormones and immunity, the Asthma may worsen in some mothers and medicines may be changed accordingly to safeguard both mother and fetus.

Heart and blood circulation system:


During pregnancy the metabolic requirement of growing fetus and host mother is very high. The baby is entirely dependent on mother for both, its nutritional requirements and excretion of wastes. To facilitate increased blood supply to the baby, there is increased demand on mother’s heart and circulatory system.

To ensure adequate blood flow certain adaptive changes happen in mother’s blood and blood vessels.

  • Hemodilution of Pregnancy:

The volume of liquid plasma rises by 40-50%, as against 30-40% increase in Red blood cells, resulting in lower viscosity of blood to facilitate easy blood flow. This is called as Hemodilution of Pregnancy. But, if the hemoglobin drops below 10gm% then it is considered as Anemia and requires intervention.

  • Vasodilation:

Under the influence of hormones, the blood vessels dilate to accommodate additional volume of around 1.5-2.0 liters of blood.

  • Heart function:

The heart pumps at faster rate with more intensity, efficiently increasing the cardiac output by 30-40%.

  • Lower Blood Pressure:

In spite of additional 2 liters of blood in circulation and increased cardiac activity, the blood pressure is maintained at lower limit. This happens as a result of dilatation of blood vessels resulting in increase in the capacity and reduction of peripheral resistance.

The blood pressure is lowered-

  • To facilitate efficient exchange of nutrients and waste products between fetus and mother.
  • To protect fetus-placental apparatus from pressure injuries.
  • Swelling in lower limbs:

The gravid uterus interferes with the return of blood flow from the lower extremities that may result in swelling in lower limbs. Prolong hanging down the legs and restricted mobility may further increase the swelling. However, physiological swelling improves with rest, limb elevation and limb exercises.

  • Blood coagulation:

Under the influence of hormones, the liver produces more coagulation factors predisposing to clot formation. The nature has designed it to prevent heavy blood loss during delivery. However, those patients who have genetic risk of hypercoagulability and are on prolonged bed rest may develop deep vein thrombosis, which is a fatal condition.

  • ECG:

The heart is displaced upward and laterally towards left, subsequently resulting in changes in ECG that can be misinterpreted as abnormal.

  • Changes in White blood cell count:

The immune system of mother is activated towards the father’s antigen in baby. This increases the WBC count. Hence, the upper normal limit during pregnancy is 15,000/cubic mm as against 10000. Only above that should be considered as infection.

What is supine hypotension syndrome?

Sleeping straight on dorsal position may lead to compression of inferior vena cava by the gravid uterus and decrease in return of blood to heart resulting in drop in maternal blood pressure, compromising maternal-fetal blood circulation. This is called as Supine Hypotension syndrome!

Hence, it is advisable to sleep in lateral positions with proper support of pillow.

The normal changes of pregnancy, such as shortness of breath, easy fatigability, malaise, palpitations (feeling own heart beat), ECG changes etc may unnecessary create suspicion of a heart disease. Hence, it needs proper evaluation to differentiate between the two.

Does pregnancy increases the risk of heart diseases?

Yes, the increased workload on heart due to increase in blood volume and cardiac activity predisposes to risk of heart failure.

Endocrine (Hormone) System:


  • Ovary, placenta and later baby produce estrogen and progesterone hormones to support and safeguard pregnancy and childbirth.
  • To ensure the overall development of the baby and to meet the increased metabolic demand of pregnancy, the requirement of thyroid hormones increases and as a result, there is increase in size and function of thyroid gland. The normal range of Serum Thyroid stimulating hormone is between 0.7-2.5 IU/L.
  • The baby is entirely dependent for its calorie requirements on glucose. To ensure the uninterrupted supply of glucose-
    • Mother develops insulin resistance so that she consumes less glucose.
    • Placenta produce insulinase enzyme to destroy insulin.
    • Increased glucose production from fats and proteins.

The alteration in glucose metabolism increases the risk of development of gestational diabetes.

Reproductive System



The non pregnant uterus is around 7x5x3 cms weighing approximately 70 grams and has a capacity of around 10 ml. Under the influence of hormones and growing fetus during the pregnancy, the uterus grows in size and capacity to easily accommodate a baby of 3 kg, amniotic liquor of 1 liter and placenta of 500 grams and weighs around 1 kg.

The blood supply during pregnancy increases from 50 ml/min in non pregnant state to around 500ml/min to facilitate optimum growth and development of fetus.


breast changes

The estrogen and progesterone hormone promotes growth and development of breast tissue to prepare it for lactation.

The pain and discomfort in breast during pregnancy is a normal complaint. Occasionally under the effect of hormones, there can be production and secretion of little watery milk from the breast.


The information is shared to create awareness towards Pregnancy and Childcare to reduce maternal and child deaths. Atmost care has been taken by the author to include the verified information from authentic sources. However, kindly discuss the same with your health care provider before implementation.