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:​​​

  1. Oakley, Celia, and Carole A Warnes. Heart Disease In Pregnancy. Malden, Mass.: Blackwell Pub./BMJ Books, 2007. Print.

  2. Editorial, AnaesthesiaUK. 'Anaesthesia UK : Physiological Changes Of Pregnancy'. Frca.co.uk. N.p., 2015. Web. 1 Oct. 2015.

  3. 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