Obstetrics Simplified - Diaa
Maternal Changes Due to Pregnancy
THE GENITAL SYSTEM
- 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.
- 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
- 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.
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.
Active, contracts, retracts and becomes thicker during labour.
Passive, dilates, stretches and becomes thinner during labour.
- 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 becomes soft, warm, moist with increased secretion and violet
in colour (Chadwick’s sign) due to increased vascularity.
It becomes soft, violet in colour. Oedema and varicosities may develop.
- 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.
This is due to increased production of melanocyte stimulating hormone
- 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
- Other areas as axilla, vulva and recent scars.
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".
There is increase in the skin blood flow and temperature.
Increase in sweat and sebaceous glands activity.
- 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).
- 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.
- 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
- 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.
- 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.
Varicosities in the lower limbs and vulva may occur due to:
- back pressure from the compressed inferior vena cava by the pregnant
- relaxation of the smooth muscles in the wall of the veins by progesterone.
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.
There is increased vascularity and tendency for bleeding as well as hypertrophy
of the interdental papilla.
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
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.
Due to reflux of the acidic gastric contents to the oesophagus.
- reduced motility of large intestine (progesterone effect),
- increased water reabsorption from the large intestine (aldosterone
- pressure on the pelvic colon by the pregnant uterus,
- sedentary life during pregnancy.
More tendency to stone formation due to atony and delayed emptying of
the gall bladder.
- mechanical pressure on the pelvic veins,
- laxity of the veins walls by progesterone,
It is displaced upwards by the enlarged uterus.
Renal blood flow and glomerular filtration rate increases by 50%.
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
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.
- 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.
- 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.
- 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
- protein bound iodine (PBI).
- TSH, free T3 and T4.
Increase in size and activity to regulate the increased calcium metabolism.
Hypertrophy particularly the cortex resulting in increased mineralocorticoids
(aldosterone) and glucocorticoids (cortisol).
- 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.
There is tendency to water retention secondary to sodium retention.
There is tendency to nitrogen retention for foetal and maternal tissues
- Pregnancy is potentially diabetogenic.
- Alimentary glucosuria may occur in early pregnancy.
- Renal glucosuria may occur in the middle of pregnancy.
There is increase in plasma lipids with tendency to acidosis.
There is increased demand for iron, calcium, phosphate and magnesium.
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Edited by Aldo Campana,