CHAPTER 17

PHYSIOLOGICAL CHANGES DURING PREGNANCY

PHYSIOLOGICAL CHANGES DURING PREGNANCY

Introduction

Pregnancy is a state in which the female body carries a fertilized ovum inside the uterus, facilitates the development of the fetus and delivers it after maturity. During this period, women’s body undergoes numerous anatomical, physiological and biochemical changes in order to fill the raised need of self and the developing fetus.

FEMALE GENITAL ORGAN

1. Vulva

• The vulva, an outermost structure becomes edematous and more vascular, under the influence of the estrogens and progesterone hormone.
• There is a temporary discoloration of the labia minora and majora to a bluish or purplish color due to increased blood flow.
• Labia majora slightly retracts, which exposes the lip and makes them look bigger in shape and size.

2. Vagina

During pregnancy, the vagina becomes edematous, hypertrophied and hyperemic. Increased blood supply leads to the violet discoloration of vaginal walls known as Chadwick’s sign or Jacquemier’s sign.

• There is an increase in mucosal thickness, the loosening of connective tissue and the smooth muscles getting hypertrophied.
• Leucorrhea: An increased thick, white vaginal discharge under the influence of estrogen hormone.
• Secretion: Larger amount of glycogen gets stored in the vaginal epithelium due to the raised level of estrogen.

3. Uterus

Changes in the anatomical dimensions of pregnancy

A. Changes in Muscles

• Hypertrophy and hyperplasia of the uterine muscles.
• Stretching of the muscles leads to the thinning of the wall at term .

B. Contractions

• Braxton-hicks are uterine contractions during pregnancy. �These contractions are irregular, infrequent, spasmodic and painless without any effect on dilatation of the cervix.
• These contractions can be felt bimanually and can be excited by rubbing the uterus.

4. Decidua

On the 23rd day of normal the menstrual cycle, there is a modelling of the endometrial stromal cells, matrix and blood vessels into the decidua for the invasion of the trophoblasts (implantation). The decidua basalis reduces from 55 mm thick at 6 weeks to 1 mm thick at 14 weeks.

• Blood supply increases by 17 times than in the nonpregnant uterus
• Uterine soufflé is the soft blowing sound synchronised with the maternal pulse because of the passing of blood through the dilated uterine blood vessels. It is heard in the lower portion of the uterus.
• Placental soufflé is a muffled ocean-like sound of blood running into the placenta.

5. Fallopian Tube

• Fallopian tube is congested and elongated.
• Muscles are hypertrophied.
• Epithelial layer get flattened and patches of decidual reaction are observed.

6. Ovaries

The corpus luteum measures about 2.5 cm at 8th week of gestation.

It secretes and regulates the estrogen and progesterone hormone before the placenta as these hormones are required for the growth of the ovum.

7. Cervix

Physiological changes in the cervix

8. Goodell’ sign or Hegar’s Sign

It is a non-specific indication of pregnancy that is characterized by the compressibility and softening of the cervical isthmus at about 6-8 weeks.

BREAST

• Size: Increased due to hypertrophy and hyperplasia of the ducts.
• Vascularity: Increased which results in the appearance of bluish veins running under the skin.
• Nipple and areola: the nipples become larger, erectile and deeply pigmented. Areola enlarges from 3 cm to 5-6 cm. Sebaceous glands become visible and hypertrophied and are called montgomery’s tubercles which surround the nipple and its secretion keep them moist and healthy.
• Secretions: Colostrum is secreted by the 12th week and become thick and yellowish by the 16th week

CUTANEOUS CHANGES

WEIGHT GAIN

BODY WATER METABOLISM

The amount of water retained during pregnancy is 6.5 litres approximately.

HAEMATOLOGICAL CHANGES

CARDIOVASCULAR SYSTEM

Cardiac Output

• It start to increase from the 5th week of pregnancy
• Cause of increase in CO: Increased blood volume.
• To meet additional needs and the increased metabolic activity during pregnancy.
• CO is lowest in the sitting position and is highest in the right or left lateral recumbent position.
• CO increases during labour.
• CO returns to the prelabour range one hour after the delivery.

Blood Pressure

• Mean arterial pressure (MAP) = Cardiac output × systemic vascular resistance.
• Overall decrease in diastolic blood pressure and Mean arterial pressure

Venous Pressure

• It decreases due to the pressure exerted by the gravid uterus on the common iliac veins, more on the right side due to dextrorotation of the uterus.

Central Hemodynamics

• Unchanged CVP, MAP, PCWP.

Supine Hypotension Syndrome

• Also known as postural hypotension.
• The gravid uterus produces a compression effect on the inferior vena cava when the patient is in a supine position resulting in a decrease in venous return leading to hypotension with signs and symptoms of bradycardia, dizziness, light-headedness, nausea and even syncope

METABOLIC CHANGES

Protein Metabolism

There is a positive nitrogenous balance. The approximate 500 grams of protein is stored in the placenta whereas 500 grams is also gained and chiefly distributed in the uterus, breasts and the maternal blood. The suppression of the breakdown of the amino acid also falls the level of urea to 15-20%.

Carbohydrate Metabolism

There is an increase in the transfer of glucose from the mother to the fetus.

Fat Metabolism

An average of 3-4 kg of fat is stored during pregnancy. It is deposited in the breasts, hip, thighs and abdominal wall. Plasma lipids and lipoproteins are increased during pregnancy under the influence of estrogens, progesterone, hPL and leptin hormone

Lipid Metabolism

• HDL level increases by 15%.
• LDL is used for the synthesis of placental steroid.
• A peptide hormone called leptin is secreted by the adipose tissue and the placenta to regulate body fat metabolism

Iron Metabolism

There is an increase in the iron requirement and is limited to the second half of the pregnancy particularly to the last 12 weeks. The total iron requirement during pregnancy is 1000 mg

SYSTEMIC CHANGES

Respiratory Changes

The enlarged uterus elevates the diaphragm by 4 cm. Thus the total lung capacity is reduced by 5% and the breathing becomes diaphragmatic. Blood volume expansion and vasodilation lead to hyperaemia and oedema of upper respiratory mucosa. Nasal congestion, epistaxis, change in the voice, and airway obstruction are chief problems exacerbated by fluid overload and pre eclampsia

Urinary Changes

Kidney

• There is dilatation of the ureter, pelvis and calyces.
• The size of the kidney increases by 1 cm.
• Renal plasma flow is increased by 50-75%.
• Glomerular filtration rate is increased by 50%.
• Decrease in maternal plasma level of creatinine, blood urea nitrogen and uric acid.

Ureters

Ureters lose the tonicity due to the high level of progesterone.

Dilatation of the ureter causing stasis is markedly observed on the right side especially in primigravidae between 20-24 weeks of pregnancy.

There is an elongation, kinking and outward displacement of the ureters

Bladders

• Hypertrophy of the muscles of the bladder wall.
• Increased frequency of micturition is observed at 6-8 weeks of pregnancy and may be normalized by 12th week of pregnancy and reappears in late pregnancy. This is because of the resetting of osmoregulation increasing water intake and polyuria.
• Stress incontinence may be observed in the late pregnancy due to urethral sphincter weakness.

Alimentary System

• Ptyalism.
• PicaAbdominal distension, bloating may also be present.
• epulis of pregnancy
• Muscle tone—decreased and exhibit sluggish peristalsis
• Gastric secretion is decreased
• Nausea and vomiting

Liver and Gall Bladder

• The functions of the liver are depressed.
• All the LFT values remain unchanged (serum bilirubin, AST, ALT, CPK, LDH) with the exception of alkaline phosphatase.
• Gall bladder distension and biliary stasis leads to gall stones under the influence of raised estrogens level.

Nervous System

• Postpartum blues, depression, and psychosis may develop.
• Mild frontal headache is observed in the first or second trimester.
• Dizziness occurs due to vasomotor instability, postural hypotension, hypoglycaemia due to long-standing or sitting.
• Carpal tunnel syndrome may appear in the later months of pregnancy.

ENDOCRINOLOGICAL CHANGES DURING PREGNANCY

Placental Endocrinology

The functions of the corpus luteum are temporarily attained by the placenta at 6-8 weeks.

Protein Hormones

There are various protein hormones produced by the pituitary, other endocrine glands and the placenta but their biological functions are different .

• Human Chorionic Gonadotropin (hCG)
• It stimulates the corpus luteum to secrete progesterone.
• It rescues the corpus luteum till 6 weeks of pregnancy.
• It stimulates the leydig cells of the male fetus to produce the testosterone hormone.
• It stimulates both adrenal and placental steroidogenesis.
• It stimulates the maternal thyroid because of its thyrotropic activity.

• Human Placental Lactogen (hPL)

It is also known as human chorionic somatomammotropin (hCS) synthesized by the syncytiotrophoblast .

Functions

• It antagonizes the insulin action as a high level of insulin helps in protein synthesis.
• It leads to maternal lipolysis and promotes the transfer of glucose and amino acids to the fetus.
• It is a potent angiogenic hormone.
• It promotes the growth of the breast for lactation .

• Pregnancy Specific beta-1 Glycoprotein (PS beta-1 G)

Functions

It is a potent immunosuppressant of lymphocytes and prevents the rejections of the product.

• Early Pregnancy Factor (EPF)

Functions

It is an immunosuppressant and prevents the rejection of the conceptus.

• Growth Factors

Functions

Immunosuppressive, paracrine and steroidogenic.

• Pregnancy Associated Plasma Protein

It is also secreted by syncytiotrophoblast. It also acts as an immunosuppressant

• Estrogens
• Among the three types of estrogens (estrone, estradiol, estriol) estriol is the major estrogen. It is synthesized by trophoblastic cells of the placenta.
• Estriol is first detectable at 9 weeks and it increases gradually to about 30 ng/mL. Low estriol is associated with fetal death, fetal, hydatidiform moles, placental sulfatase or aromatase deficiency.

STEROIDAL HORMONES

• Progesterone
• The placenta uses cholesterol as a precursor to produce pregnenolone.
• Pregnenolone undergoes enzymatic reaction in the endoplasmic reticulum to produce the progesterone. The daily production is about 250 mg in normal pregnancy. Progesterone is not detectable after 24 hours of delivery. There are various conditions associated with levels of progesterone

Functions of the Steroidal Hormones

Pituitary Gland

Thyroid

Morphological Changes

Hyperplasia leads to the enlargement of the thyroid gland.

Physiological Changes

• Renal clearance of iodine is increased due to increased GFR, ultimately decreasing the maternal serum iodine level.
• Stimulatory effect of the hCG causes hyperplasia of the gland.
• WHO recommended the iodine intake during pregnancy from 100–150 μg/ml/day to 200 μg/ml/ day.
• There is an increase in BMR by 25% during the last trimester.

Adrenal Cortex

Morphological Changes

Slight enlargement of the adrenal cortex particularly the thickness of the zona pellucid is increased.

Physiological Changes

• A marked increase in the serum levels of the aldosterone, deoxycorticosterone, CBG, cortisol and free cortisol.
• The doubling of CBG is due to the high estrogen level.
• Fetal cortisol rises 3 times the non-pregnant values.
• The level of corticotrophin-releasing hormone increases markedly.

Parathyroid Gland

Morphological Changes

Hyperplasia of gland

Physiological Changes

PTH remains unchanged. The main functions of PTH are to regulate the renal synthesis of 1,25 dihydroxy vitamin D3 and mobilization of calcium from bone. Calcitonin opposes the action of PTH and vitamin D.

PTH does not cross the placenta but the calcium ions do cross against a concentration gradient.

Pancreas

Physiological Changes

There is hyperinsulinism, particularly during third trimester which coincides with the peak concentration of placental hormones. The postprandial insulin level is increased whereas the fasting insulin concentration is reduced.

Serum hormone levels