Physiological Changes During Pregnancy

The human body makes physiological changes during pregnancy. in this article, you will find an overview of physiologic changes in different systems of our body.

What is the Purpose of the Change?

  • To provide nutrient and oxygen to the baby
  • Provide a supportive environment to the baby
  • Dispose of metabolic waste
  • Protect from infection, toxin and trauma. Eg protects mom from male fetus testosterone.
  • Prepare the mother for delivery – Eg ligament and joint mobility increased which help the mother to deliver vaginaly.
  • Prepare breast milk
  • To accommodate the fetus (the baby is the antigen for the mother normally but the uterus manage to bear the fetus until delivery). So what are the changes?

Changes in the Cardiovascular System

Changes in cardiovascular system are

  • Heart rate increase throughout the pregnancy.
  • Heart size also increases by 12% that means intracardiac volume also increase too.
  • Blood volume increase by 50%. That is because of hormones called estrogen and progesterone produced by the placenta. Estrogen stimulated a system called the renin-angiotensin system which makes a kidney retain more water and salt. The purpose of an increase in blood volume is to increase blood flow to the fetus. It also helps the mother to stabilize from the blood loss during delivery (normally blood loss during vaginal delivery is 500 ml and after c-section is 1000 ml.)
  • Cardiac output increase by 40% and stroke volume increased by 25 – 30%. The main purpose of increase CO and SV is some organs need more blood supply during pregnancy. For eg: – Blood flow to the uterus increased by 250%, to the kidney increase by 35%, and the breast by 200ml/min.

Changes in the Respiratory System

Changes in respiratory system are

  • Normally during pregnancy, the diaphragm will be pushed upward by 4 cm and the ribcage displaced upward. so lower thoracic diameter increase by 2 cm and thoracic circumference by 6 cm.
  • Tidal volume increase by 40% and inspiratory volume by 10%.
  • Carbon dioxide concentration of arterial blood decrease and oxygen concentration increase because of hyperventilation which helps the baby get more oxygen. Fetal hemoglobin by itself has more affinity for oxygen than carbon dioxide.
  • Progesterone also affects the brain decrease threshold of the central chemoreceptor which increases sensitivity. That is protective to the baby in a way because the baby will not be exposed to increased co2 levels.

Changes in the Renal System

Changes in renal system are

  • Length of kidney increases by 1.5cm.
  • Ureter enlongated, widen and become more curved because of progesterone (dilate smooth muscle)
  • Renal blood flow increases so GFR increases up to 60% during pregnancy which helps the kidney to excrete more toxins out of the body.

Weight Gain During Pregnancy

Depending on prepregnancy body mass index, the mother expect to gain weight during pregnancy
average weight gain is 12.5 kg or 27.5 lb.

Pre preganancy BMIExpected Weight gain
<18.512.5 – 18.5 kg
18.5 – 2512.5 kg
>257 – 10 kg

All these physiological changes during pregnancy are there to help both the mother and the baby to handle the pregnancy period.

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