Physiological changes in pregnancy

Endocrinal changes :

a) Placental hormones

During pregnancy, two important hormones are produced from syncytiotrophoblast.


Beta-HCG

Used as a marker for pregnancy (through urine/serum). Can be detected starting from 8-10 days from conception.
Role in early pregnancy is to maintain corpus luteum, hence secretion of estrogen and progesterone can be continued to maintain pregnancy, until placenta is sufficiently develop to replace function of corpus luteum.

Human Placental Lactogen

Acting as a "growth hormone" of pregnancy.
Provides alternative maternal source of energy by increasing fatty acid mobilisation, reducing maternal utilisation of glucose.
Hence, more glucose can be diverted for fetus to meet nutritional demands.

b) Pituitary gland

The size of pituitary gland enlarges, causing headache
Levels of ACTH - low
Oxytocin - low (until labour)
Vasopressin - low
Increased number of prolactin secreting cells - Increased serum prolactin

c) Thyroid gland

Size of thyroid gland increases during pregnancy.
Due to increased blood flow, and follicular hyperplasia, frank goitre may occur sometimes.
However, mother is euthyroid (T3 and T4 normal)
Increased serum TBG level

d) Parathyroid gland

Increased PTH secretion, leading to increased calcium absorption.

e) Adrenal gland

No increase in size of adrenal gland.
Cortisol and other corticosteroid secretion increases.

f) Pancreas

Increased size of Langerhan's cell
Increased number of B-cells
Increased insulin secretion
Increased insulin resistance

Hematological changes

Both plasma volume and RBC production increases during pregnancy.
However, plasma volume expansion outweights RBC production, leading to physiological dilutional anemia.

Renal excretion of folate increases during pregnancy. Hence, demand for folate increases.

WBC count increases during pregnancy.

Pregnancy is a hypercoagulable state, in order to prevent excessive blood loss during 3rd stage of labour (delivery of placenta).
However, it increases the risk of mother towards venous thromboembolic disease.

Cardiovascular changes

Heart rate is increased by 10-20%
Stroke volume is increased by about 10%
Since Cardiac output = HR X SV, hence, cardiac output increases about 35-50% in pregnancy.

Despite increased in SV and CO, BP doesn't increase.
In fact, due to hormonal-induced vascular smooth muscle relaxation, peripheral vascular resistance reduces for 30-35%.
Hence, mean arterial pressure during pregnancy reduces for about 10%.

Respiratory system changes

Divided into mechanical changes and biochemical changes.
For mechanical changes, the anatomy of thoracic cage is changed.
The rib cage is pushed upwards, transverse diameter increased.
Hence, it causes :

Increased Tidal volume
Decreased Residual volume
And decreased Vital capacity

An increased in tidal volume causing decrease in PCO2 and slight increase in PO2.
Hence, blood pH is increased, and to prevent significant alkalosis, renal excretion of bicarbonate ion increases.

Changes in the renal system

During pregnancy, urinary tract is dilated. (relaxation of smooth muscles)
Hence, this increases the risk of ascending urinary tract infection during pregnancy.

Renal blood flow increases, eventually causing increase in GFR.
Hence, more excretion of blood substances through urine.
Plasma urea and creatinine levels are slightly lower than in non-pregnant state.

Protein excretion through urine increases.
Renal threshold for glucose reduces - glycosuria (normal)

Changes in alimentary system

Increased appetite
Increased craving for food
Increased gastric emptying time
Increased heart burn
Increased constipation
Increased esophageal reflux

Decreased gastric secretion
Decreased intestinal motility
Decreased gastric motility

Category: Featured , Obstetrics Notes