Prepared by:Fadziyah zaira bte md fadzil,

4th year, MBBS,Gef international medical school,

Bangalore,India

Physiology of Pregnancy

Introduction

During pregnancy there is progressive anatomical and physiological changes not only confined to the genital organs but also all systems of the body.

Principally, this a phenomenon of maternal adaptation to the increasing demands of the growing fetus.

Genital organ changes

Vulva Edematous and hyperaemic Superficial varicosities may appear especially

multipara. Labia minora- pigmented, and hypertrophied.

Vagina Hypertrophied Edematous and more vascular. Bluish discoloration of the mucosa (Jacquemier’s

sign) Due to increased blood supply of the venous plexus.

Length of anterior vaginal wall increased.

Contd.

Vaginal secretion Copious, thin and curdy white

Due to marked exfoliated cells and bacteria. pH becomes acidic (3.5—6)

Due to more conversion of glycogen into lactic acid by Lactobacillus acidophilic consequent on high estrogen level.

Prevents pathogenic infection

Vaginal cytology Preponderance of navicular cells (small intermediate

cells with elongated nuclei) in cluster.

Uterus

At term 900-1000gm at weight 35cm in length

Changes occur at all parts of uterus Body Isthmus Cervix

Uterus-cont

Body of uterus There is increase in growth and enlargement of the

body of the uterus.

Enlargement Factor affecting the enlargement of the uterus.

1. Change in the muscles1. Hypertrophy and hyperplasia-first half of pregnancy2. Stretching of muscle fibre beyond 20 wks of

pregnancy.

Uterus-cont

2. Arrangement of the muscle fibres1. Outer longitudinal-hoodlike arrangement2. Intermediate-thickest and strongest, criss-cross

arrangement3. Inner circular-scanty, sphincter-like arrangement.

3. Simultaneous increase in number and size of supporting fibrous and elastic tissue.

4. Increased vascularity1. Ovarian artery carries more blood during pregnancy2. Markes spiraling of the arteries-maximum at 20 wks

and then straigthen up and becomes dilated.

Arrangement of muscle fibres during pregnancy

Uterus-cont

Shape of the uterus Pyriform Globular – at 12 wks Pyriform – by 28 wks Spherical – beyond 36 wks

Position Normal anteverted upto 8 weeks. Erect afterwards

Lateral obliquity Uterus enlarged and rotates to the right (dextrorotation)

Uterus-cont

Uterine peritoneum Maintains relation proportionately with the growing

uterus.

*Braxton-Hicks contraction spontaneous uterine contraction in pregnancy that occur

from early weeks of pregnancy. Irregular, infrequent, spasmodic and painless without any

effect on dilatation of the cervix.

Uterine endometrium Changes from non-pregnant uterus into decidua of

pregnancy.

Uterus-cont

Isthmus 1st trimester, isthmus hypertrophies and elongates to

about 3 times its original length. >12 weeks, it progressively unfolds from above

downwards. Circularly arranged muscle fibres in this region acts

as sphincter that helps in retaining the fetus within the uterus.

Uterus-cont

Cervix Stroma:

Hypertrophy and hyperplasia Fluid accumulation Increased vascularity-bluish colouration(Chadwick’s

Sign) Softening of the cervix (Goodell’s sign)

Epithelium Marked proliferation of the endocervical mucosa with

downward extension beyond squamocolumnar junction.

Uterus-cont

Secretion Copious and tenacious (leucorrhea of pregnancy) Due to effect of progesterone Mucus forms thick plug to seal cervical canal.

Cervical length Unaltered but cervix becomes bulkier.

Advantage of having mucus plug formed during pregnancy

Other organs

Fallopian tube Held vertical by side of the uterus Total length is increased Tube becomes congested Epithelium is flattened Patches of decidual reaction observed

Ovary Persistent growth of the corpus luteum until 8th wks

and then regresses following decline of HCG secretion from the placenta.

It becomes colloid degeneration at 12 wks and later becomes calcified at term.

Breasts

Changes are best evident in primigravidae.Size

increased due to marked hypertrophy and proliferation of the ducts and the alveoli

Nipples and areola Larger, erect, deeply pigmented Montgomery tubercles-hypertrophied sebaceous

glands that is visible in the areola during pregnancy. Secondary areola- outer zone of less marked and

irregular pigmented area that appear at 2nd trimester.

Breast changes

Pigmented, erect nipple

Montgomery tubercles

Secondary areola

Secretion Can be squeezed out at 12th wks which is sticky at

first. 16th wks-it becomes thick and yellowish. Later-colostrum may be expressed from the nipples.

Cutaneous changes

Face Chloasma gravidarum/pregnancy mask

Abdomen Linea nigra - brownish black pigmented area in the

midline from xiphisternum to symphysis pubis. Striae gravidarum – slightly depressed linear marks

with varing length and breadth. Striae albicans- glistening white scar tissue after

delivery

Chloasma gravidarum

Linea Nigra

Striae gravidarum

Weight gain

Early wks pt may lose weight because of vomiting.

Subsequent months, the weight gain is progressive until last one or two wks where weights becomes static.

Total weight gain during course of single pregnancy for healthy woman is 11 kg.

1kg rise during first trimester, 5kg each during subsequent trimesters.

Weight gain-cont

Retention of electrolytes- sodium, potassium and chlorides.

Retention of Na+ causes water retention.At term, nearly 6.5liters water is retained.

Importance of weight checking Rapid gain in weight of more than 0.5kg a week/>2kg

a month is maybe an early manifestation of pre-eclampsia and need for careful supervision.

Stationary / falling weight- IUGR/intrauterine death of fetus.

Body water metabolism

Pregnancy is a state of hypervolemia.Causes of sodium retention and volume overload are

Changes in osmoregulation Increased estrogen and progesterone Increased renin angiotensin activity Increased aldosterone Atrial natriuretic peptide.

Resetting of osmotic threshold for thirst and ADH secretion.

Increased water intake due to lowered osmotic threshold for thirst causes polyuria in early pregnancy.

Hematological changes

Blood volume Markedly raised Increased from 6th wks, expands rapidly tp maximum

40-50% above nonpregnant level at 30-32 wks.

Plasma volume Increases to 1.25liters

RBC and Hb RBC volume increased 20-30% Total volume increase: 350ml

Hematological changes

Hemodilution occur during pregnancy and fall in Hb concentration.

Advantage of hemodilution during pregnancy Diminished blood viscosity thus optimum gaseous

exchange between mama and baby Protection from the mother against the adverse

effects of blood loss during pregnancy.

Hematological changes

Leucocytes Neutrophilic leucocytosis Due to increased estrogen and cortisol

Total protein Increases from normal 180gm to 230gm at term A:G ratio is diminished to 1:1

Blood coagulation factor Pregnancy is hypercoagulable state. Fibrinogen level is raised by 50% 4-fold rise in ESR

Heart and circulation

Anatomical changes Heart is pushed upwards and outwards

CO Increased from 5th wks of pregnancy reaches peak 40-

50% at 30-34wks. Caused by

Increased blood volume To meet additional O2 required due to high metabolic

activity during pregnancy

BP Decreased due to decreased vascular resistance

Heart and circulation

Venous pressure Femoral venous pressure is markedly increased due to

pressure exerted by gravid uterus on the common iliac veins.

Central hemodynamics No significant change in CVP, MAP, and PCWP.

Postural hypotension Compression of gravid uterus to IVC and failed

collateral circulation (parasternal and azygos veins)

Heart and circulation

Regional distribution of blood flow Uterine blood flow increased to 750ml/min near term. Pulmonary BF increased by 2500ml/min Renal BF increased by 400ml/min

Explains flushing, sweating or stuffy nose in pregnancy.

Metabolic changes

General metabolism increased due to needs of growing fetus BMR increased to extent of 30% higher

Protein metabolism Positive nitrogenous balance throughout pregnancy Anabolism!

Carbohydrate metabolism Insulin secretion increased Sensitivity of insulin receptor reduced To ensure continous supply of glucose to fetus

Metabolic changes

Fat metabolism 3-4kg fat stored at abdoment,breast, hips and thighs.

Lipid metabolism HDL level increased by 15% LDL utilised for placental steroid synthesis.

Iron metabolism Pregnancy is an iron deficiency state Absorption from gut is increased but lost along the

routes, to placenta and during delivery. Serum iron and ferritin will fall if supplementation is

not given.

Systemic changes

Respiratory system Breathing becomes diaphragmatic Transverse diameter of chest expends by 2 cm Chest circumference increased by 5-7cm Mucosa of URT shows congestion Hyperventilation occur due to increased tidal volume

and progesterone acting at the respiratory center.Acid base balance

PCO2 fall, PO2 rises- facilitate transfer of gases between mam and baby

pH rises- respiratory alkalosis due to high maternal O2 consumption and fetal demand.

Systemic changes

Urinary system Dilatation of ureter and renal pelvis Kidney enlarges by 1cm Renal plasma flow increased by 50-75%

Alimentary system Muscle tone and motility of entire GI tract are

diminished due to increased progesterone level Cardiac sphincter relaxes chemical esophagitis and

heart burn Diminished gastric secretion

Systemic changes

Liver and gallbladder Functions are depressed except LFT serum levels.

Nervous system Psychological changes-nausea, sleeplessness Postpartum blues, depression or psychosis

Summary

There is various changes happening in a pregnant mother, not only at specific organs, but also systemically.

It is important to know these changes so we as doctors should assure them that the changes are normal whenever they have doubt about what’s happening to their own body.