Physiological Changes in Pregnancy Study Guide

Physiological Changes in Pregnancy

Study guide:

Changes occur in the mother’s body to provide for fetal needs, and to prepare the maternal body for labour & delivery. Here are some of those changes according to the bodily systems:

Cardiovascular :

With the upward displacement of the diaphragm, the apex is moved anteriorly & to the left:

- ECG findings: left axis deviation, depressed ST segments & inversion or flattened T-waves in lead III.

Cardiac output increases starting from week 6 – 8 of gestation, reaching a 30 – 50% increase by 32-34 weeks.

- Progesterone & oestrogen acting on the renin-angiotensin & aldosterone pathways: Retaining water & sodium

- Increases stroke volume by 25 – 35%

- Contractility remaining unchanged.

- Left ventricular hypertrophy & dilatation

- This increase enables uterine blood flow to meet growing nutritional & oxygenation needs of the foetus. It also enables blood loss (average 500 ml) at delivery without decompensation.

Oestrogen & progesterone causes vasodilatation:

- Resulting in a fall in peripheral vascular resistance by about 20% early in pregnancy.

- Postural hypotension may occur.

- Consequently heart rate increases by 15 – 25%

- Blood flow to kidneys, skin & mucosa increases.

Diastolic& systolic blood pressures tend to fall during mid pregnancy, which return to normal by week 36.

Haematological:

Renal erythropoietin increases red cell mass by 20-30%

- Which is a smaller rise than that in plasma volume.

- Resulting in haemodilution (physiological anaemia of pregnancy).

Serum iron ↓ falls whilst transferrin & total iron binding capacity rise↑.
↑ white cell count rises & peaks after delivery.

Pregnancy induces a hypercoagulable state:

- ↑ concentration of clotting factors & fibrinogen.

- ↓ fibrinolytic activity decreases.

- Platelet production is ↑.

- Platelets count ↓because of dilution & consumption; function remains normal.

Endocrine:

Insulin production & response ↑:

Blood sugar level usually remains normal, or sometimes becomes low.
Sometimes the insulin response is met with resistance caused predominantly by human placental lactogen.

- Follicular stimulating & luteinising hormones ↓

- ACTH & melanocyte-stimulating hormone ↑

- Prolactin ↑

Preparing the mother for breastfeeding.

- Thyroxine-binding globulin (TBG) ↑

- T4 & T3 ↑ over the first half of pregnancy but slightly ↓ during the pregnancy due to ↑ TBG-binding

- Serum calcium levels ↓, stimulating an increased production of parathyroid hormone (PTH↑ ).

- Cortisol levels ↑:

Favouring lipogenesis & fat storage

Alimentary (Gastrointestinal):

Appetite is usually ↑, sometimes with specific cravings.
Many women are prone to heartburn because:

- Progesterone causes relaxation of the lower oesophageal sphincter & increases reflux.

- The uterus causes a gradual upward displacement of stomach & intestines, which increases intragastric pressure & changing the angle of the gastroesophageal junction.

Serum alkaline phosphatase increases up to 3 times normal, as a result of placental production.
Serum albumin ↓.
Gastrointestinal motility is ↓& transit time is longer to increase nutrient absorption.

-Therefore, constipation is common.

↓ in the gallbladder contractility:

- Predisposition to forming cholesterol gallstones.

Gums become spongy, friable & prone to bleeding.

Respiratory:

The diaphragm is progressively displaced upward by the uterus.

- Moves with greater exertion during breathing.

Breathing is mainly diaphragmatic.
Lung capacities:

- Total lung capacity ↓slightly

- Inspiratory reserve volume is increased but FEV1 remain unchanged

- Tidal volume ↑

- ↑ vital capacity & ↓ residual volume

Capillary engorgement & oedema of the upper airway down to the pharynx, false cords, glottis & arytenoids (due to hormonal changes).
Respiratory rate usually doesn’t increase.
Increased oxygen consumption by approximately 20%
Airway resistance is ↓due to progesterone-mediated bronchial & tracheal smooth muscle relaxation
State of compensated respiratory alkalosis.

Metabolic:

The basal metabolic rate éslowly during pregnancy by 15 – 20%.
In women with normal BMIs, energy requirement:

- Does not increase significantly during the 1st trimester.

- ↑350 kcal/day in the 2nd trimester.

- ↑500 kcal/day in the 3rd trimester.

Normal weight gain is approximately 12.5 kg.

Renal:

Renal plasma flow & glomerular filtration rate (GFR) éprogressively during pregnancy, reaching 50-60% higher at term:

- Mild glycosuria &/or proteinuria is viewed as normal.

- ↑ clearance of urea, creatinine, urate & excretion of bicarbonate.

Plasma osmolality ↓ because of water retention.
Kidneys increase in length & ureters become longer, more curved & with an increase in residual urine volume.
Pregnant women are more prone to urinary tract infections because of progesterone-mediated smooth muscle relaxation of the renal pelvis, ureters, & bladder:

- 5% of pregnant women have bacteriuria, often asymptomatic.

- Symptomatic or not you have to treat.

Dermatological:

Hyperpigmentation of the umbilicus, nipples, abdominal midline (linea nigra) & face (chloasma) due to hormonal changes.
Spider naevi & palmar erythema may be seen.
Striae gravidarum ('stretch marks') are common.

Musculoskeletal:

Increased ligamental laxity caused by increased levels of relaxin.
Shift in posture with exaggerated lumbar lordosis leading to the typical gait of late pregnancy

References:

Oakley, Celia, and Carole A Warnes. Heart Disease In Pregnancy. Malden, Mass.: Blackwell Pub./BMJ Books, 2007. Print.
Editorial, AnaesthesiaUK. 'Anaesthesia UK : Physiological Changes Of Pregnancy'. Frca.co.uk. N.p., 2015. Web. 1 Oct. 2015.
Said, J. M. et al. 'Altered Reference Ranges For Protein C And Protein S During Early Pregnancy: Implications For The Diagnosis Of Protein C And Protein S Deficiency During Pregnancy'. Thromb Haemost 103.5 (2010): 984-988. Web. 1 Oct. 2015.

Written by: Abeer AlKhairy.

Reviewed by: Roaa Amer.

Format editor: Roaa Amer

Sara Qubaiban

Web Publisher: Adel Yasky