Physiological Changes

6-Physiological changes

During pregnancy

Volume homeostasis

. The rapid expansion of blood volume begins at 6–8 weeks gestation and plateaus at 32–34 weeks gestation. While there is some increase in
intracellular water, the most marked expansion occurs in extracellular fluid volume, especially circulating plasma volume.
This expanded extracellular fluid volume accounts for between 8 and 10 kg of the average maternal
weight gain during pregnancy

Physiologic anaemia

. Overall, total body water increases from 6.5 to 8.5 L by the end of pregnancy.
the larger increase of plasma volume relative to erythrocyte volume results in haemodilution and a physiologic anaemia

Na-retention

Outside of pregnancy, sodium is the most important determinant of extracellular fluid volume. In pregnancy, changes in osmoregulation and the renin-angiotensin system result in active sodium reabsorption in renal tubules and water retention.

Factors contributing to fluid retention

• Sodium retention.


• Resetting of osmostat.


• ↓ Thirst threshold.


• ↓ Plasma oncotic pressure.
Consequences of fluid retention


• ↓ Haemoglobin concentration.


• ↓ Haematocrit.


• ↓ Serum albumin concentration.



• ↑ Stroke volume.


• ↑ Renal blood flow.

Another feature of this change in fluid balance is that plasma osmolality decreases by about 10 mOsmol/kg.
Whereas in the non-pregnant state such a decrease would be associated with a rapid diuresis in order to maintain volume homeostasis, the pregnant woman appears to tolerate this level of osmolality

Plasma oncotic pressure

Is mainly determined by [albumin ] , and this decreases by about 20 %
As plasma oncotic pressure partly determines the degree to which fluid passes into and out of capillaries, its decrease is one of the factors responsible for the increase in glomerular filtration rate (GFR) during pregnancy and probably contributes to the development of peripheral oedema,a feature of normal pregnancy

Blood/Haematology

Maternal haemoglobin levels are decreased because of the discrepancy between the 1000 to 1500 mL increases in plasma volume and the increase in erythrocyte mass, which is around 280 mL.
Transfer of iron stores to the fetus contributes further to this physiological anaemia.
The mean[ haemoglobin] falls from
13.3 g/dL in the non-pregnant state to 10.9 g/dL at the 36th week of normal pregnancy.

Renal clearance of folic acid increases substantially during normal pregnancy and plasma folate concentrations fall


platelet count
usually remains stable throughout pregnancy.
Increases in the platelet count have been reported in the first week postpartum and this may contribute to the increased risk of thromboembolic complication sin this period.

Haemostasis and coagulation

Pregnancy is a hypercoagulable state, which returns to normal around 4 weeks after delivery. Almost all procoagulant factors, including factors VII, VIII, IX, X and XII are increased during pregnancy.
Fibrinogen is increased by 50 per cent

Biochemistry

Plasma protein concentrations, particularly albumin,are decreased during normal pregnancy, which affects :-
the plasma oncotic pressure
the peak plasma concentrations of drugs that are highly protein bound

Oxygen consumption increases by about 45 mL/min during the course of pregnancy, which represents an increase of about 20% from oxygen consumption at rest (300 mL/min).

Cardiovascular system

Signs and symptoms of pregnancy mimic those of heart disease. Elevation of the diaphragm,adjustments of lung volumes and increases in minute ventilation give rise to breathlessness. Oedema in the extremities is a common finding, and results
from an increase in total body sodium and water,
as well as venous compression by the gravid uterus. Which aisocause decreased venous return to
the heart, leading to light-headedness and syncope.
Palpitations are common and usually represent sinus tachycardia, which is normal in pregnancy


In normal pregnancy, cardiac output increases as early as 5 weeks gestation (3 weeks after conception)
and rises to around 40 per cent above the prepregnancy baseline by 24 weeks, i.e. from about 5.0 to 7.0 L/min when

The increase in cardiac output is caused partly by an increase in heart rate, which is detected first as early as 5 weeks, and partly by an increase in stroke volume.
A progressive increase in heart rate continues until the third trimester of pregnancy, when rates are typically 10–15 beats per minute greater than those found in the non-pregnant state.

Decreases in diastolic blood pressure (10–

15 mmHg) are more marked during the antenatal period than the decrease in systolic pressure
(5–10 mmHg). Thus, early pregnancy is associated
with a relative increase in pulse pressure.
An 11%fall in mean arterial blood pressure at rest. Later, diastolic blood pressure increases to levels that are at least equivalent to those found in the non-pregnant state

Changes in reference values in normal pregnancy.

Non-pregnant Pregnant (term)
Haemoglobin (g/dL) 13.3 11.0
Haematocrit (%) 38–45 32–34
White cell count (109/L) 4–11 6–14
Fibrinogen (mg/dL) 300 450
Platelets (109/L) 140–440 150–400
Ferritin (g/L) 17–320 4.8–43.5
Sodium (mmol/L) 132–144 127–140
Potassium (mmol/L) 3.5–5.0 3.3–5.4
Urea (mmol/L) 4.3 3.1
Creatinine (mol/L) 73 64
Uric acid (mol/L) 246 269 (186–401)
Albumin (g/L) 37–48 23–38
Alanine aminotransferase (IU/L) 4–40 6–28
Alkaline phosphatase (IU/L) 30–130 133–418
Bilirubin (mol/L) 2–20 3.0–19.4
Triglycerides (mmol/L) 0.3–1.7 1.6–5.8


summery
Decreases in:
• haemoglobin concentration;
• haematocrit;
• plasma folate concentration;
• protein S activity;
• plasma protein concentration;
• creatinine, urea, uric acid.
Increases in:
• erythrocyte sedimentation rate;
• fi brinogen concentration;
• activated protein C resistance;
• factors VII, VIII, IX, X and XII;
• D-D-dimers; • alkaline phosphatase.

The maternal brain

Women frequently report problems with attention,concentration and memory during pregnancy and in the early postpartum period.
While these associations are well established, particularly the decline in memory in the third trimester,

Respiratory tractAirway

The neck, oropharyngeal tissues, breasts and chest wall
are all affected by weight gain during pregnancy.
This, as well as breast engorgement and airway oedema,
can compromise the airway leading to difficulty
with visualization of the larynx during tracheal
intubation.
The vascularity of the respiratory tract mucosa increases and the nasal mucosa can be both oedematous and prone to bleeding.
During pregnancy this is often perceived as congestion and rhinitis


Cardiovascular system
The cardiac output is elevated at the onset of
labour to over 7.0 L/min, rising further within labour,
with a 30 per cent increase in demand in the fi nal
stages .
This increase is due to the uterine contractions each of which squeezes 300–500 mL of blood into the maternal circulation.
At delivery,a shift of blood from the empty uterus into the
maternal circulation – called autotransfusion – causes
an increase of 10–20 per cent in the cardiac output.

Ausculatory changes

The first heart sound is loud and sometimes split, while a third heart sound is audible in 84 per cent of pregnant women by 20 weeks
An ejection systolic murmur can be heard in 96 per cent of apparently normal pregnant women

Key points

Cardiovascular changes
• ↑ Heart rate (10–20 per cent).
• ↑ Stroke volume (10 per cent).
• ↑ Cardiac output (30–50 per cent).
• ↓ Mean arterial pressure (10 per cent).
• ↓ Pulse pressure.
• ↓ Peripheral resistance (35 per cent).


Gastrointestinal changes

Oral

Elevated circulating oestrogen and progesterone levels are implicated in increasing vascular permeability and decreasing immune resistance, thereby increasing susceptibility to
Gingivitis (erythema,oedema, hyperplasia and increased bleeding of the gingival tissue). .

Gut
As gestation advances, the uterus displaces the stomach
and intestines upwards, which can hinder diagnosis of
intra-abdominal surgical events as well as confound
the routine abdominal examination.
Elevated progesterone levels reduce lower oesophageal sphincter tone and increase the placental production of gastrin, increasing gastric acidity.
These changes combine to increase the incidence of refl ux oesophagitis and heartburn, which affect up to 80 per cent of pregnant women.

The kidneys and urinary tract1-Anatomic changes

The kidneys increase in size in normal pregnancy,with a 1–2 cm change in length. The calyces, renal pelvis and ureters dilate, giving the usually incorrect impression of obstruction.
By the third trimester, over 80 per cent of women have some evidence of stasis or hydronephrosis, which is more marked on the right side due to uterine dextrorotation

2-Functional changes

Glomerular fi ltration rate (GFR) rises immediately after conception and increases by about 50 per cent overall, reaching its maximum at the end of the fi rst trimester. GFR then falls by about 20 per cent
in the third trimester,
Renal blood flow increases by up to 80 per cent in the second trimester, due to the combination of increased cardiac output and increased renal vasodilatation, but this is followed by a 25 per cent fall towards term


Key points
Renal changes
• ↑ Kidney size (1 cm).
• Dilatation of renal pelvis and ureters.
• ↑ Blood flow (60–75 per cent).
• ↑ Glomerular fi ltration (50 per cent).
• ↑ Renal plasma flow (50–80 per cent).
• ↑ Clearance of most substances.
• ↓ Plasma creatinine, urea and urate.
• Glycosuria is normal.

Reproductive organsUterus

Uterine blood fl ow increases 40-fold to
700 mL/min at term
Oestrogen mediates the adaptation of the uterine
smooth muscle to pregnancy. High levels of maternal oestradiol and progesterone induce both hyperplasia and hypertrophy of the myometrium, increasing the weight of the uterus from 50–60 g prior to pregnancy to 1000 g by term.

By the third trimester, the uterus is described in lower and upper segments.

the lower segment It is thinner, contains less muscle and fewer blood vessels and is the site of incision for the majority of Caesarean sections

specialized cellular connections also develop with increasing gestation.

These intercellular gap junctions allow changes in membrane potential to spread rapidly from one cell to another, facilitating the spread of membrane depolarization, and subsequent
myometrial contraction


Cervix
The cervix is described as looking bluer due to its increased vascularity. oestradiol;stimulates growth of the columnar epithelium of the cervical canal. This becomes visible on the ectocervix and is called an ectropion, which is prone to contact bleeding.

Breasts and lactation

Deposition of fat around glandular tissue occurs,
and the number of glandular ducts is increased
by oestrogen, while progesterone and (hPL) increase the number of gland alveoli.
Prolactin is essential for the stimulation of milk secretion and during pregnancy prepares the alveoli for milk production.
Towards the end of pregnancy, and in the early puerperium,the breasts produce colostrum, a thick yellow secretion rich in immunoglobulins.

The rapid fall in oestrogen concentration

over the fi rst 48 hours after delivery removes this
inhibition and allows lactation to begin.
Lactation is initiated by early suckling, which stimulates the anterior and posterior pituitary to release prolactin and oxytocin, respectively.
[prolactin]
estrogen
No lactation


prolactin promotes breast engorgement and the alveoli become distended with milk. Oxytocin released from the posterior pituitary causes contraction in myoepithelial cells surrounding the alveoli and small ducts, squeezing milk towards the nipple.

Endocrine changes

• ↑ Prolactin concentration.
• Human growth hormone is suppressed.
• ↑ Corticosteroid concentrations.
• ↓ TSH in early pregnancy.
• ↓ fT4 in late pregnancy.
• hCG is produced.
• Insulin resistance develops.

MetabolismWeight gain

1-(fetus, placenta, amniotic fl uid),
2-various maternal tissues (uterus,breasts, blood, extracellular fl uid),
3-and the increase in maternal fat stores.
The increase in weight is largely fluid, with today body water increasing by around 8 L
Ranges of weight gain recommended for women with low pre-pregnancy BMI (20) are 12.5–18.0 kg, compared to 11.5–16.0 kg for those with normal pre-pregnancy BMI (20–26)

Skin

Hyperpigmentation can be localized or generalized
and affects almost 90 per cent of pregnant women,
being more obvious in women with darker skin


The linea alba darkens to a brown line along themidline of the abdomen, which reaches the symphysispubis, and is called the linea nigra



Melasma, also called chloasma, is an acquired hypermelanosis characterized by symmetrical, irregular, macular brown-grey pigmentation of the face, reported in up to 75 per cent of pregnant women.











Striae gravidarum (stretch marks) occur in mostpregnant women, usually by the end of the secondtrimester, with a reported incidence of 90 per centin Caucasians.

Key points

Skin changes
• Hyperpigmentation.
• Striae gravidarum.
• Hirsuitism.
• ↑ Sebaceous gland activity


Thank you

1- the following parameters increase during normal pregnancy except :

• Hemoglobin production
• Hemoglobin concentration
• Plasma volume
• GFR
• Oxygen demand
• 2- during normal pregnancy there is reduction in
• a. Oncotic pressure
• Prolactin production
• Estrogen level
• Cardiac output
• None of the above