PHYSIOLOGICAL CHANGES IN PREGNANCY

Various systems affected

• Reproductive organ changes
• Cardiovascular changes
• Hematological changes
• Respiratory changes
• Changes in urinary system
• Endocrine organ changes

Reproductive organs

• Vagina
• Cervix
• Uterine corpus
• Breast

Vagina

• Increased vascularity and hyperaemia of mucosa
• Increased thickness of mucosa, increased loosening of connective tissue, hypertrophy of muscles -increase in length and distensibility

• Increased vaginal secretions, acidic medium with increased lactobacillus

Cervix

Pronounced softening and cyanosis –after a month of pregnancy (Goodell’s sign)

- increased vascularity & edema

- cervical glandular hypertrophy /hyperplasia

- rearangement of collagen with decrease in mechanical strength at term

Thick mucus – bloody show at labour

Uterus

Hypertophy and dilatation

normal 70gm ----------------10ml cavity

pregnant 1100gm -------------5litres

Increase in size is contributed by

muscle hypertrophy, hyperplasia, stretching

increased vasculature/lymphatics

Firm uterus –> soft in early pregnancy -> distensible muscular sac in late pregnancy

• Change in size & shape

pear shaped –> almost spherical at around 3rd month-> oval in shape in later pregnancy

Size : hens egg at 6 weeks

cricket ball at 8 weeks

Asain pear at 10 weeks

out of pelvis after 12 weeks

• Dextrorotation ? Due to rectosigmoid on the left side

Change in contractility

painless contractions from as early as first trimester

detectable by second trimester ( Braxton Hicks)

painful, regular, increasing in intensity and frequency – labour

• Uteroplacental flow

uteroplacental flow is increased in pregnancy

450-750ml/min late in pregnancy. This is required to maintain an adequate placental perfusion.

• Endometrium

Decidual reaction –3 layers differentiation

trophoblast formation

Isthmus

• Hypertrophy ,elongation in first trimesterto three times its length

in second tri- gradually taken up and incorporated into the uterine corpus.

The circular muscles in region act as sphincter

Respiratory changes

ANATOMICAL

* diaphragm rises by 4 cm

* compensatory increase in thoracic transverse diameter by 2 cm

* Increase in circumference of the thorax

Pulmonary function

• Respiratory rate – relatively no change
• Vital capacity (3.2L) – almost unaltered
• Pulmonary vascular resistance is decreased (Progesterone effect)
• Residual volume – decreases by 20%
• Tidal volume (485ml) _ increases by 40%
• Airway conductance is increased, oxygen requirement is increased

Respiratory

Increased respiratory effort (dyspnoea)

arterial PCO2 is decreased and O2 is increased

facilitates O2 transfer to fetus

Respiratory diseases may worsen in pregnancy as O2 requirement in pregnancy increases

Urinary system

Kidney:

increase in size by 1 cm

dilatation of pelvis, calyces and ureter

GFR (50% increase) increases throughout pregnancy

renal perfusion increases by 25-50% in early pregnancy

So serum urea and creatinine values decrease in normal pregnancy.

Urine

• Glycosuria- decrease in renal threshold,

persistent glycosuria – possibility of DM

• Proteinuria - not evident in pregnancy

except in slight amounts after labour/puerperium

• Hematuria – UTI, difficult labour, instrumental delivery

Ureter

Hydronephrosis and hydroureter due to effect of progesterone

RIGHT SIDE more than left

* cushioning by the sigmoid colon on the left

* right ovarian vein crosses the ureter obliquely

Elongation , angulation and lateral displacement of ureters by gravid uterus

Comes back to normal in 6 – 8 weeks post partum

Bladder

Few changes before the 4th month

Gravid uterus, pelvic congestion - causes

bladder trigone to be elevated, thickening of interureteric ridge and also rest of bladder,

increased tortuosity and size of vessels in mucosa

In late pregnancy, especially engaged head pushes base of bladder forward increasing the congestion , oedema and increase susceptibility to trauma and infection.

Post delivery esp vaginal – stress incontinence by urethral sphincter damage

CARDIOVASCULAR

ANATOMICAL

Heart is elevated and rotated towards left- causes apex to move more lateral and cardiac silhouette to appear larger

HEART SOUNDS

Splitting of first sound

Third sound heard loudly

Systolic murmur in 90% cases - disappear shortly after delivery

Continuous murmur (10%) – b/o increase in breast vasculature

ECG –left axis deviation

Cardiac output

Increase due to increase maternal weight, blood vol. increase, increased BMR

CO = SV X HR (minimal change)

Starts from early pregnancy (10weeks), increases cont upto 28weeks –

Max at 32 weeks – slight decrease towards term - increase in labour – decreases in postpartum

CO 4.5L - 6.2 L in pregnancy(30-40%)

CV changes

Blood pressure – remains same due to decrease in peripheral resistance

Mid pregnancy drop of 5-10 mmHg can occur due to pooling of blood in uteroplacental circulation.

More marked in hypertensives

Towards term –supine hypotension – gravid uterus compresses IVC – decreases venous return -hypotension

Venous system – pressure by gravid uterus and progesterone

- distensibility of veins

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pedal oedema,varicose,haemorrhoids

thrombosis

Circulation – increased blood flow to uterus, kidneys, skin & lungs

In uterus 50ml /min in non pregnant to 750ml/min at term

Haematological changes

Blood volume : increases by 40%

* meet demand of increased uterus

* protect mother and fetus against deleterious effects of decreased VR

* safeguards the mother against effects of blood loss in delivery

Blood volume - increased plasma volume (40%)

- increased RBC volume (33%)

Haemodilution-

mean Hg falls from 13.3gm/dl in non preg to 10.9g/dl in pregnant .

<11gm/dl of Hg – anaemic

Hypercoagulable state

increase in plasma fibrinogen ,with increased rouleaux formation, decreased fibrinoltic activity

Haematological

• WBC increased - 5 to 12000/cmm in pregnancy

14-16000/cmm in puerperium

even up to 20000/cmm

• ESR increases (x4 times)

• Blood protein : serum albumin level decreases by 30 % . Plasma protein conc decreases –decreased colloidal oncotic pressure

Iron metabolism

Iron content is decreased – increased erythropoiesis & increased transfer to fetus

Total iron needed

Increase in RBC (450ml) = 500mg

transfer to fetus = 300mg

insensible loss = 200mg

Total = 1000mg

Compensatory efforts are not sufficient

Metabolic changes

• Weight gain : total about 12.5kg
• 1 lb/week after 20 weeks

Water metabolism

• Fundamental change in pregnancy is fluid retention.
• Total about 6.5L of fluid is retained

Protein metabolism

• Protein gain in pregnancy

500gm –fetus /placenta

500gm – contractile proteins, breast, Hb and plasma proteins

Protein supplementation in diet is needed, but along with carbohydrate & fat

Carbohydrate metabolism

• Potentially diabetogenic

mild fasting hypoglycemia

post prandial hyperglycemia

hyperinsulinemia

All this to ensure a maintained supply of glucose to fetus

Insulin resistance could be due to ? Insulinase enzyme

Endocrine changes

• Pituitary

increase in size

increase in GH – weight gain in preg

increased ADH and oxytocin

leading to oedema of pregnancy

Thyroid gland

• Increase in size –hyperplasia of gland
• TSH increase which causes hyperplasia, increase in BMR beginning from the third month
• Increased Estrogen- increased TBG conc and binding capacity- increased serum protein bound iodine and Increase in circulatory T 4 and T 3

Adrenal gland

• Slight increase in size-mainly cortex
• Increase in level of serum cortisol, aldosterone
• which could be responsible for the edema of pregnancy

Important Questions:

Q1.During CS, anaesthetist puts the patient in the left lat position. Why?

Answer: Supine Hypotension

Q2.In a heart dis prgnant patient –most dangerous time is ?

Answer: Second stage of labor

Q3.USG done in a pregnant woman at 30 weeks shows hydronephrosis ? What will you do?