Uteroplacental Blood Flow

The delivery of most substances essential for the growth and metabolism of the fetus and placenta, as well as the removal of most metabolic wastes, is dependent upon adequate perfusion of the placenta. Placental perfusion is dependent in turn upon the blood flow to the uterus through the uterine and ovarian arteries.

The enlarged uterus presses on the inferior venacava and the lower aorta (blood vessels) when the patient lies supine (on the back), causing slight hypertension and this is called "supine hypertension" in pregnancy. Hence it is advisable that she should lie on her left side to prevent increase in blood pressure.

Kidney

The kidney undergoes tremendous anatomic and physiologic changes during pregnancy. With advancing gestation, the enlarging uterus can compress the ureters as they cross the pelvic brim and cause further dilatation by obstructing the flow of urine. These changes may contribute to the frequency of urinary tract infections during pregnancy.

Respiratory system

Hormonal changes may cause swelling of the lining in the nose, oropharynx, larynx, and trachea. Symptoms of nasal congestion, voice change and upper respiratory tract infection may prevail throughout gestation.