Physiological Changes During Pregnancy

Physiological Changes During Pregnancy
1. Cardiovascular System-

  • Circulating blood volume increase, plasma volume increase and total red blood cell volume increase (Total volume about 40% to 50%)
  • Physiological anaemia occurs as the plasma increase exceeds the increase in red blood cells production.
  • Iron requirement are increase.
  • Heart size is increase and is elevated upwards and to the left because of displacement of the diaphragm as the uterus enlarges.
  • Blood volume increase>1.5 litter.
  • Pulse may increase about 10-15 beats/minute.
  • Blood pressure may decline in second trimester due to decrease in systemic vascular resistance due to smooth muscle relaxing effect of progesterone.
  • Cardiac output increase.
  • The disproportionate increase in plasma and RBC volume produces a state of hemo-dilution during pregnancy.
  • Hemo-dilution cause diminished blood viscosity which ensure optimum gaseous exchange between the maternal and fetal circulation.
  • ESR increase due to decrease blood viscosity.
Volume (ml) Non-pregnancy Preg.Near term Change
Blood volume 4000 5500 +30%-40%
Plasma volume 2500 3750 +40%-50%
RBC volume  1400 1750 +20%-30%
Plasma Protein (gm) 180 230 +20-30%

Respiratory System

  • Oxygen consumption increase by 15% to 20%
  • Diaphragm is elevated because of enlarge uterus.
  • Respiratory Rate remains unchanged.
  • Breathing becomes Diaphragmatic.

Gastro-Intestinal systemic

  • Nausea and vomiting due to HCG
  • Poor appetite due to decrease gastric motility.

Renal system

  • Frequency of urination occurs as a result of pressure of enlarge uterus on the bladder.
  • GFR is increase by 50%

Endocrine System

  • BMR rises
  • Thyroid enlarges slightly and thyroid activity increase.

Reproductive System


  • Enlarge, increase in mass from 60mg to 1000mg.
  • Irregular contraction occurs.
  • 12th Week: The fundus of the uterus may be palpated abdominally above the symphysis pubis.
  • 16th Week: The uterus reaches half way between the symphysis pubis and the umbilicus and the shape is ovoid.
  • 20th Week: The uterus is two fingers below umbilicus.
  • 24th Week: Fundus is at the level of umbilicus or one finger lower level of umbilicus.
  • 30th Week: The lower uterine segment can be identified. It is still not complete but can be defined as that portion lying below the reflection. The fundus lies between the umbilicus and xiphisternum.
  • 36th Week: The uterus now reaches its highest level at the xiphisternum (near subcostal arch).
  • 38th Week: The fundus sinks down to the subcostal arch below ensiform cartilage, the level of 34th week pregnancy. This is called ‘lightening’ .
  • 40th Week: The lower uterine segment gets relaxed and stretched whereas the cervix is shortened and soft. The uterus is now ready for labour


  • Increase vascularization cause blue discoloured of the cervix= Chadwick's Sign.


  • Breast size increase.
  • Nipple becomes pronounced.
  • Sebaceous gland which remain invisible in the non- pregnant state in the areola because hyper trophied and are called Montgomery Tubercles. these are placed surrounding the nipple. their secretion keeps the nipple and areola moist and healthy.
  • Secondary Areola appears in 20th weeks.

Cutaneous Changes

  • Pigmentation increase.
  • A dark down the midline of the abdomen may appear that is Linea Nigra (20 weeks)
  • Cholera (pregnancy mask)-A blotchy brownish hyper pigmentation, may occur over the forehead, check and nose (24 weeks)-Butterfly sign
  • Reddish-purple stretch marks (Striae)may occur on the abdomen, breast. thigh and upper arms(20 weeks)


  • Fating hypoglycemia (due to fetal consumption)
  • Poat-parandal hypoglycemia (due to anti-insulin factor like Oest, progesterm. prolactin)
  • 3-4 kg fat is stored during pregnancy mostly in the abdomen wall,breast,hips and thigh.

Acid-Base Balance

  • Arterial Pco2 fall from 40mm/Hg to 32 mm/Hg
  • Arterial Pco2 rises 95mm/Hg to 105 mm/Hg.
  • This facilitates transfer of CO2 from the fetus to the mother and co2 from mother to fetus.
  • Pregnancy is a state of Respiratory Alkalosis.

Weight Gain-

  • In early weeks weight loose because of nausea and vomiting.
  • Total weight gain for a healthy woman during pregnancy is average -11kg.
  • In first trimester=1kg
  • In second trimester=5kg
  • In third trimester=5kg
  • Reproductive weight gain-
  • Fetus=3.3kg
  • Placenta=0.6kg
  • Amniotic fluid=0.8kg
  • Uterus=0.9kg
  • Breast=0.4kg


  • Net maternal weight gain-
  • Increase in blood volume =1.3kg
  • Increase in extracellular fluid =1.2kg
  • Accumulation of fat and protein=3.5kg


  • Periodic and regular weight checking is important to detect abnormality.
  • Rapid weight gain more than 0.5kg a week or more than 2kg a month,may be the early sign of pre-Eclampsia.
  • Falling weight suggests IUGR or IUD of fetus.
  • Ideally weight gain is depends on pre-pregnancy body mass index(BMI)
  • Weight gain for women with normal BMI(20-25)=11 to 16kg
  • Obese women (BMI>26)=<7kg
  • Under weight women(BMI<19)=gain upto 18 kg

Body water metabolism-

  • The amount of water Retained at term is about=6.5 litter.
  • The water content of fetus,placenta and amniotic fluid is about 3.5 liter.
  • Pregnancy is the sate of Hypervolemia.
  • There is active Retention of sodium and potassium due to-increase Oestrogen and progesterone.
  • -Increase Renin and Angiotensin activity.
  • -Control by ADH