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Obstetrics Simplified - Diaa M. EI-Mowafi

Maternal Changes Due to Pregnancy

THE GENITAL SYSTEM

The Ovaries

  • Both ovaries are enlarged due to increased vascularity and oedema particularly that containing the corpus luteum.
  • Corpus luteum starts to degenerate after the 10th week when the placenta is formed.
  • Corpus luteum secretes oestrogen, progesterone and relaxin.
  • Relaxin is a protein hormone. Its exact role in pregnancy is unknown. It may induce softness and effacement of the cervix.
  • Ovulation ceases during pregnancy due to pituitary inhibition by the high levels of oestrogen and progesterone.

The Fallopian Tubes

The musculature hypertrophies and the epithelium becomes flattened.

The Uterus

  • Size: increases from 7.5´ 5 ´ 2.5 cm in non-pregnant state to 35 ´ 25 ´ 20 cm at term.
  • Weight: increases from 50 gm in non-pregnant state to 1000 gm at term. This is due to:
    • hypertrophy of the muscle fibres (oestrogen effect) and their multiplication (progesterone effect).
    • increase in the mass of elastic connective tissue.
  • Capacity: increases from 4 ml in non-pregnant state to 4000 ml at term.
  • Shape: becomes globular by the 8th week and pyriform by the 16th week till term.
  • Position: with ascent from the pelvis, the uterus usually undergoes rotation with tilting to the right (dextro-rotation), probably due to presence of the rectosigmoid colon on the left side.
  • Consistency: becomes progressively softer due to:
    • increased vascularity, (ii) the presence of amniotic fluid.
  • Contractility: from the first trimester onwards, the uterus undergoes irregular contractions called Braxton Hicks Contractions, which normally are painless. They may cause some discomfort late in pregnancy and may account for false labour pain.
  • Uteroplacental blood flow: uterine and ovarian vessels increase in diameter, length and tortuosity. Uterine blood flow increases progressively and reaches about 500 ml/ minute at term.
  • Formation of lower uterine segment: After 12 weeks, the isthmus (0.5cm) starts to expand gradually to form the lower uterine segment which measures 10 cm in length at term.
  Upper Uterine Segment Lower Uterine Segment

Peritoneum

Firmly-attached.

Loosely-attached.

Myometrium

3 layers; outer longitudinal, middle oblique and inner circular. The middle layer forms 8-shaped fibres around the blood vessels to control postpartum haemorrhage (living ligatures).

2 layers; outer longitudinal and inner circular.

Decidua

Well-developed.

Poorly-developed.

Membranes

Firmly-attached.

Loosely- attached.

Activity

Active, contracts, retracts and becomes thicker during labour.

Passive, dilates, stretches and becomes thinner during labour.

The Cervix

  • It becomes hypertrophied, soft and bluish in colour due to oedema and increased vascularity.
  • Soon after conception, a thick cervical secretion obstructs the cervical canal forming a mucous plug.
  • The endocervical epithelium proliferates and / or everted forming cervical ectopy (previously called erosion).

The Vagina

The vagina becomes soft, warm, moist with increased secretion and violet in colour (Chadwick’s sign) due to increased vascularity.

The Vulva

It becomes soft, violet in colour. Oedema and varicosities may develop.

THE BREASTS

  • In the early weeks, the pregnant woman experiences tenderness and tingling of the breasts.
  • After the second month the breasts increase in size and become nodular as a result of hypertrophy of the mammary alveoli. Delicate veins become visible beneath the skin.
  • The primary areola becomes deeply pigmented. The nipples become larger, deeply pigmented and more erectile.
  • Montgomery’s follicles, which are hypertrophic sebaceous glands, appear as non-pigmented elevations in the primary areola.
  • Nearly after the third month colostrum, which is a thick yellowish fluid, can be expressed from the nipples.
  • During the fifth month, a pigmented area appears around the primary areola called secondary areola.

THE SKIN

Pigmentation

This is due to increased production of melanocyte stimulating hormone (MSH).

  • Chloasma gravidarum (pregnancy mask): A butterfly pigmentation appears on the checks and nose. It usually disappears few months after labour.
  • Breasts: increased pigmentation of the nipples and primary areolae and appearance of the secondary areolae.
  • Linea nigra: A dark line extending from the umbilicus to the symphysis pubis.
  • Other areas as axilla, vulva and recent scars.

Striae gravidarum

These are reddish, slightly depressed streaks appear in the later months of pregnancy in the abdomen and sometimes breasts and thighs. It may be due to mechanical stretching or increased glucocorticoids which results in rupture of the elastic fibres in the dermis and exposure of the vascular subcutaneous tissues. After delivery, they become white in colour but do not disappear and called "striae albicans".

Vascular changes

There is increase in the skin blood flow and temperature.

Secretions

Increase in sweat and sebaceous glands activity.

HEMATOLOGIC CHANGES

Blood Volume

  • The total blood volume increases steadily from early pregnancy to reach a maximum of 35-45% above the non-pregnant level at 32 weeks.
  • Plasma volume increases by 40% whereas red cell mass increases by 20% leading to haemodilution (Physiological anaemia).

Blood Indices

  • Erythrocytes: decrease during pregnancy from 4.5 millions to 3.7 millions /mm3 relative to the increase in plasma volume. Its contents from 2,3 diphosphoglycerate increase which competes for oxygen binding sites in the haemoglobin molecule thus release more O2 to the foetus.
  • Haemoglobin concentration: falls from 14 gm/dl to 12 gm/dl.
  • Leucocytes: increases from 7000/mm3 to 10.500/mm during pregnancy and up to 16000/mm3 during labour.
  • Fibrinogen: increases from 200-400 mg/dl to 400-600 mg/dl.
  • Erythrocyte sedimentation rate: increases from 12 to 50 mm/hour.

CARDIOVASCULAR SYSTEM

Heart

  • Position: As the diaphragm is elevated progressively during pregnancy the apex is displaced upwards and to the left so that it lies in the 4th intercostal space outside the midclavicular line.
  • Rate: The resting pulse rate increases by 10-15 beats per minute during pregnancy.
  • Cardiac output: increases mainly by increased stroke volume rather than increased heart rate reaching a maximum of 40% above the non-pregnant level at 20 weeks to be maintained till term.
    • During labour cardiac output increases more, particularly during the second stage due to pain, uterine contractions and expulsive efforts pushing the blood into the general circulation.
    • Postpartum, the increased COP is maintained for up to 4 days and then declines rapidly.

Arteries

  • Arterial blood pressure usually declines during the second trimester due to peripheral vasodilatation caused by oestrogens and prostaglandins.
  • The posture of the pregnant woman affects arterial blood pressure. Typically, it is highest when she is sitting, lowest when lying in the lateral recumbent position and intermediate when supine.
  • Supine hypotensive syndrome may develop in some women late in pregnancy in supine position. This is due to compression of the inferior vena cava by the large pregnant uterus resulting in decrease venous return, decrease cardiac output and low blood pressure that fainting may occur.

Veins

Varicosities in the lower limbs and vulva may occur due to:

  • back pressure from the compressed inferior vena cava by the pregnant uterus,
  • relaxation of the smooth muscles in the wall of the veins by progesterone.

RESPIRATORY SYSTEM

Dysponea may occur due to:

  • increase sensitivity of the respiratory center to CO2 possibly due to high progesterone level,
  • elevation of the diaphragm by the pregnant uterus.

GASTROINTESTINAL TRACT

Gingivitis

There is increased vascularity and tendency for bleeding as well as hypertrophy of the interdental papilla.

Ptyalism

It is excessive salivation and more common in association with oral sepsis.

Nausea and vomiting

Nausea (morning sickness) and vomiting (emesis gravidarum) occur in early months.

Appetite changes (longing or craving)

The pregnant woman dislikes some foods and odours while desires others. Reduced sensitivity of the taste buds during pregnancy creates the desire for markedly sweet, sour or salt foods. Deviation may be so extreme to the extent of eating blackboard chalk, coal or mud (pica).

Indigestion and flatulance

This is probably due to:

  • decreased gastric acidity caused by regurgitation of alkaline secretion from the intestine to the stomach,
  • decreased gastric motility.

Hurt burn

Due to reflux of the acidic gastric contents to the oesophagus.

Constipation

Due to:

  • reduced motility of large intestine (progesterone effect),
  • increased water reabsorption from the large intestine (aldosterone effect),
  • pressure on the pelvic colon by the pregnant uterus,
  • sedentary life during pregnancy.

Gall stones

More tendency to stone formation due to atony and delayed emptying of the gall bladder.

Haemorroids

Due to:

  • mechanical pressure on the pelvic veins,
  • laxity of the veins walls by progesterone,
  • constipation.

Appendix

It is displaced upwards by the enlarged uterus.

URINARY SYSTEM

Kidney

Renal blood flow and glomerular filtration rate increases by 50%.

Ureters

Dilatation of the ureters and renal pelvis due to:

  • relaxation of the ureters by the effect of progesterone,
  • pressure against the pelvic brim by the uterus particularly on the right side.

Bladder

Frequency of micturition in early pregnancy due to:

  • pressure on the bladder by the enlarged uterus,
  • congestion of the bladder mucosa.

Urinary stress incontinence may develop for the first time during pregnancy and spontaneously relieved later on.

MUSCULO-SKELETAL SYSTEM

  • Progressive lordosis to compensate for the anterior position of the enlarged uterus.
  • Increased mobility of the pelvic joints due to softening of the joints and ligaments caused by progesterone and relaxin.

ENDOCRINE SYSTEM

Pituitary gland

  • The anterior pituitary enlarges due to an increase in prolactin secreting cells (lactotrophs).
  • Prolactin level increases up to 150 ng/ml at term to ensure lactation.

Thyroid gland

  • There is diffuse slight enlargement of the gland.
  • Gland activity increases as evidenced by the increase in:
    • basal metabolic rate (BMR) by about 30%,
    • thyroxine-binding globulin, total T3 (tri-iodothyronine) and T4 (thyroxine),
    • protein bound iodine (PBI).
    • TSH, free T3 and T4.

Parathyroid glands

Increase in size and activity to regulate the increased calcium metabolism.

Adrenal glands

Hypertrophy particularly the cortex resulting in increased mineralocorticoids (aldosterone) and glucocorticoids (cortisol).

METABOLIC CHANGES

Weight gain

  • The average weight gain in pregnancy is 10-12 kg.
  • This increase occurs mainly in the second and third trimesters at a rate of  350-400 gm/week.
  • Six kg of the average 11 kg weight gain is composed of maternal tissues (breast, fat, blood and uterine tissue) and 5 kg of foetus, placenta and amniotic fluid.
  • Of  this 11 kg, 7 kg are water, 3 kg fat and 1 kg protein.

Water metabolism

There is tendency to water retention secondary to sodium retention.

Protein metabolism

There is tendency to nitrogen retention for foetal and maternal tissues formation.

Carbohydrate metabolism

  • Pregnancy is potentially diabetogenic.
  • Alimentary glucosuria may occur in early pregnancy.
  • Renal glucosuria may occur in the middle of pregnancy.

Fat metabolism

There is increase in plasma lipids with tendency to acidosis.

Mineral metabolism

There is increased demand for iron, calcium, phosphate and magnesium.