Physiological changes in pregnancy: uterus, vagina, cardivascular system, blood, respiratory function Flashcards
Uterus
§ Body enlargement due to hypertrophy and hyperplasia under the influence of oestrogen and progesterone.
§ Shape changes from non-pregnant piriform
globular in 12 weeks piriform /ovoid in 28 weeks
spherical in 36 weeks.
§ Non-pregnant uterus ~100 g, while pregnant one 1000 g at term. Cavity expands from 4 mL to 4000 mL.
§ Involution is rapid over first 2 weeks after delivery but slows after and is not completed by 2 months.
§ Increased blood supply/hypervascularity by arborization, spiralling of arteries under the influence of
progesterone and veins become dilated and valveless.
§ Increased blood flow from 50 ml/min to 500 ml/min.
§ Isthmus hypertrophies, elongates to 3x the original length and softens, forms lower uterine segment and site
of C-sections due to its avascularity.
§ Trophoblast invasion and subsequent decidual reaction: pale, large cells that form the decidua basalis,
parietalis forming the maternal component of placenta.
§ Progesterone maintains quiescence by increasing the resting membrane potential of myometrial cells.
§ Normal contractions during pregnancy are painless and felt as ‘tightening’ (Braxton Hick contractions).
Cervix
Increased vascularity of the cervix by arborization and hypertrophy of cervical glands.
§ Reduced collagen in 3rd trimester, accumulation of water and glycosaminoglycans for cervical ripening.
§ Increased mucus production. Increased viscosity of mucus : thick, white curdy.
§ Vulva becomes more edematous, hyper-vascularize and labia minora are pigmented and hypertrophied.
Vagina
§ Hypertrophied, edematous, hypervascularized and collagen decreases while glycosaminoglycans increase.
§ Increased blood supply of venous plexus surrounding the walls gives bluish colour to the mucosa called the
Jacquemier’s Sign and length of anterior vaginal wall is increased.
§ Thick, white curdy secretion with low pH (3.5-6) to prevent infections yet some infections occur ‘Candidata’.
Cardiovascular system
Heart enlarges by 70-80 mL (stroke volume increases) and CO increases from by 40% in the 1st Trimester.
§ HR increases by 15 bpm due to progesterone-driven hyperventilation.
§ Pregnancy imposes increase in CO and is likely to precipitate heart failure in women with heart disease.
§ Increase in the ventricular volume results in dilation of valve-rings and increase regurgitant flow velocities.
§ Myocardial contractility increases during pregnancy, indicated by shortening of pre-ejection period.
§ BP falls in the first half of pregnancy, implying a very substantial reduction in TPR.
§ Decreased TPR (by 50%) to expand blood volume à Mean Blood Pressure reduces till mid trimester.
Associated with expansion of vascular space in uteroplacental bed and renal vasculature (vasodilation).
§ Gap between 4th and 5th Korotkoff sounds widens in pregnancy and 5th sound may be difficult.
It is
recommended to use 5th sound where it is clear and 4th sound where the point of disappearance is unclear.
§ Consequence can be Supine Hypotension when mother lies on her back (due to restriction in venous return)
Blood
Increased in RBC, WBC, total plasma proteins but platelet count falls due to dilution effect, and their
reactivity increases 2nd and 3rd trimesters.
§ Erythropoietin increases during pregnancy; increase in the demand of oxygen during pregnancy.
§ Disproportionate increase in plasma and RBC volumes produces state of haemodilution (fall in haematocrit
and Hb), while serum iron falls (physiological anaemia) but absorption of iron from gut increases. Plasma
folate concentration halves by term due to high renal clearance.
§ Massive neutrophilia during puerperium and cannot be assumed to be due to infection.
§ Increase in plasma clotting factors (VII, VIII, VIII:C) while factors II and V are constant, and increased
tendency to clot in pregnancy.
Plasma fibrinogen rises from 3rd month of pregnancy.
However, the
concentrations of protein S falls during first two trimesters.
Respiratory Function
§ Diaphragm elevation and chest expansion displacing apex of the heart displaced upwards and left
laterally causing changes in T wave in lead 3 and Q waves in lead 3 and aVF.
§ Vital capacity increases ~300 mL.
§ The increased alveolar ventilation results in a small rise in maternal PO2.
This increases is offset by
rightward shift of maternal oxyhaemoglobin dissociation curve caused by an increase in 2,3 DPG in
erythrocytes as this facilitates oxygen unloading to the fetus.
§ Increased minute ventilation and tidal volume with constant respiratory rate of 14-20 to compensate for
increased O2 requirement, because of hyperventilation women feel shortness of breath.
§ Hyperaemic and edematous mucosa of nasopharynx.
