Reference ranges for blood tests in pregnancy

Complete Blood Count (CBC) – Interpretation

The interpretation of test results is for information only and is not intended as a substitute for medical diagnosis or treatment by a health practitioner.

The Administration of the website cannot be held responsible for possible negative consequences associated with self-diagnosis, self-treatment or inaction.

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A Complete Blood Count (CBC) also known as a Full Blood Count (FBC) is one of the most common blood tests in the laboratory. A Complete Blood Count (CBC) Test gives vital information through numerical values of the key blood components such as red blood cells (RBC), white blood cells (WBC), platelets (PTL). A CBC also helps your doctor diagnose conditions, such as anemia, infection, and many other disorders. Normal and abnormal physiologic changes that may occur during pregnancy and the laboratory values that indicate these changes.

Red blood cells (RBC) carry oxygen from the lungs to the rest of the body. If the RBC count is low (anemia), the body may not be getting the oxygen it needs. The hemoglobin molecule fills up the red blood cells. It carries oxygen and gives the blood cell its red colour.

White blood cells (also called leukocytes) function as part of the body’s immune system. They help to protect the body from infection and disease. There are different types of white blood cells: Neutrophils, Lymphocytes (B cells and T cells), Monocytes, Eosinophils, and Basophils. The white blood cell differential shows if the number of cells are in proper proportion to one another, and if there is more or less of one cell type.

Platelet count forms part of the Full Blood Count (FBC) panel of tests and may reveal the reason for easy bruising or bleeding problems.

Complete Blood Count (CBC) components: RBC count, hemoglobin (Hb or Hgb), hematocrit (Hct), MCV, MCH, MCHC, platelets, WBC count (leukocytes) – neutrophils, lymphocytes, monocytes, eosinophils, basophils, erythrocyte sedimentation rate (ESR). Reference Ranges for lab values during pregnancy, cbc levels in pregnancy.

What is the thyroid gland and how does it work?

The thyroid gland lies in the front of your neck just below your Adam’s apple. It is made up of two lobes, on either side of your windpipe, joined by a small bridge of thyroid tissue called the isthmus. The thyroid secretes two main hormones into the bloodstream. One of these is thyroxine, which contains four atoms of iodine and is often called T4. This in turn is converted to tri-iodothyronine (T3), which contains three atoms of iodine. It is the T3 that is biologically active and regulates your body’s metabolism.

The amount of T4 and T3 secreted by your thyroid gland is regulated by the pituitary gland, which lies underneath your brain. The pituitary senses the level of thyroid hormones in your bloodstream, just as the thermostat in your living room senses the temperature. If the level drops just a little below normal the pituitary reacts by secreting a hormone called thyroid-stimulating hormone (TSH), which activates the thyroid gland to produce more T4. When the thyroid hormone levels rise above normal, the ‘thermostat’ senses this and the pituitary stops secreting TSH so that the thyroid makes less T4. TSH is also called thyrotropin.

What are thyroid function tests?

The usual blood tests done for thyroid function are TSH, T4 and sometimes T3. A blood sample is taken from a vein in the arm and sent off to the laboratory for analysis. Usually the ‘free’ or active portion of T4 and T3 is measured (i.e., FT4 and FT3). Laboratories use reference ranges to compare blood test results with results in the normal healthy population. Typical reference ranges for healthy adults are:

In pregnancy the serum TSH reference range is different from the general population and should ideally be based on reference ranges derived from healthy pregnant women in the same population. Where such pregnancy reference ranges are unavailable a TSH range of 0.4–2.5 mU/l in the first trimester and 0.4–3.0 mU/l in the second and third trimesters can be used.

These ranges are only a guide and will vary according to laboratory. There are different reference ranges for testing babies and young children.

How can blood tests be used to diagnose thyroid disorders?

Your doctor will interpret these tests, together with your symptoms and how you feel, in order to diagnose whether you have a thyroid disorder, how severe it is, and how to treat it. If your TSH and FT4 results are outside the reference range your doctor may order additional tests.

TSH and FT4

If the TSH level is high and the FT4 result is low this suggests an under-active thyroid (hypothyroidism) that requires treatment.

If the TSH level is low and the FT4 result is high this suggests an over-active thyroid (hyperthyroidism) that requires treatment.

If the TSH level is slightly raised but the FT4 level is still within the normal reference range this is called subclinical hypothyroidism or mild thyroid failure. It may develop into overt or clinical hypothyroidism; an additional test for thyroid antibodies will help to determine the risk. Some people with subclinical hypothyroidism, particularly those whose TSH level is greater than 10 mU/l, may benefit from treatment with levothyroxine.

A low TSH with a low FT4 may be a result of a failure of the pituitary gland (secondary hypothyroidism caused by hypopituitarism) or a response to a significant non-thyroid illness

This is only used in testing for hyperthyroidism or assessing its severity.

Thyroid antibodies

If the initial thyroid test results show signs of thyroid dysfunction and if there is a suspicion of an autoimmune thyroid disease, one or more thyroid antibody tests may be ordered. The main thyroid antibodies are thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb), and thyroid stimulating hormone receptor antibodies (TSHR Ab formerly known as TRAb). There is no standard reference range for thyroid antibodies because this depends on many different factors.

Other more specialised tests are thyroglobulin (Tg) (used in monitoring people who have been treated for differentiated thyroid cancer) and calcitonin (used in monitoring people with medullary thyroid cancer).

How can blood tests be used to manage thyroid disorders?

The aims of treatment are to make you feel better and to ensure that you come to no long-term harm from your thyroid hormone replacement. The blood test for TSH, which is the most sensitive marker of your thyroid status, is used as a biochemical marker to ensure that your thyroid hormone replacement is adequate.

The recommended target range for TSH for patients on thyroid hormone replacement should preferably be within the reference range. Over-replacement may cause long-term harm to the cardiovascular system and the bones. The exception is thyroid cancer where the aim in selected patients is to keep the TSH level suppressed just below the reference range (usually to 0.1-0.5 mU/L).

Occasionally patients only feel well if the TSH is below normal or suppressed. This is usually not harmful as long as the FT3 is clearly normal. There are also certain patients who only feel better if the TSH is just above the reference range. It is recommended that each patient is treated as an individual and in conjunction with their supervising doctor is set a target that is right for them and their particular circumstances.

If you have been diagnosed with hypothyroidism you will start treatment with levothyroxine – a synthetic version of the thyroxine (T4) produced by the thyroid gland.

If you have hyperthyroidism the available treatments are antithyroid drugs to reduce the production of thyroid hormones; surgery to remove all or part of the thyroid gland; or radioactive iodine to reduce the activity of the thyroid. Your doctor will discuss treatment options with you.

At the start of treatment your doctor will carry out blood tests usually every few weeks. The results will help to fine-tune your treatment. You will normally have less frequent tests when you are stable on your treatment. In hypothyroidism, a TSH test once a year will check that levels are within the reference range. In hyperthyroidism the usual tests are TSH and FT4; how often these take place will depend on the treatment.

You will have additional tests if the results are abnormal, and you should tell your doctor about any change in your health between blood tests. If your results are normal, but you still don’t feel entirely well, ask your doctor whether there is room for a slight adjustment of your dose. This can be considered if your TSH level can be kept within the reference range. You should not, however, alter your dose without discussing this with your doctor.

Once you start on levothyroxine it may take several months before your symptoms improve even if the tests are biochemically satisfactory. This is especially the case in patients with a history of Graves’ disease who may have been hyperthyroid for many months and who may take a considerable time to adjust to feeling ‘normal’ with biochemically satisfactory tests following radioiodine or surgery.

What can affect the results of thyroid function tests?

Thyroid function tests can be influenced by medications and illnesses. Let the person taking your blood test know of anything that might affect the readings, especially:

  • Any serious illness such as heart attack, infection, trauma, serious liver disease or kidney failure
  • Medication used to treat thyroid disorders, especially when taking too much or too little
  • Any other medication you are taking, including: the contraceptive pill, steroid hormones, anticonvulsants, anti-inflammatory drugs, lithium (used for certain mental disorders) and amiodarone (used to control irregularities of the heart beat)

When should I have a thyroid function blood test?

You should make an appointment with your GP and ask for a blood test if you have:

  • Symptoms of an over- or under-active thyroid
  • Swelling or thickening in the neck
  • An irregular or fast heart rate
  • High cholesterol (which causes atherosclerosis – a build-up of fat in the arteries)
  • Osteoporosis (fragile or thinning bones)
  • Fertility problems, abnormal menstrual cycles, recurrent miscarriage, low libido
  • Family history of autoimmune disorders, e.g., type 1 diabetes, vitiligo, etc
  • Feeling unwell after having a baby
  • Planning pregnancy or in early pregnancy (and you have a family history or personal history of thyroid disorders, a past history of postpartum thyroiditis, or type 1 diabetes)

You should have a blood test once a year, or more frequently if your doctor advises, if:

  • You have a diagnosed thyroid disorder
  • You have had previous treatment for an over-active thyroid (radioactive iodine, thyroid surgery, medication)
  • You have had irradiation to the head and neck after surgery for head and neck cancer
  • Before you have treatment with amiodarone or lithium, then 6-12 months during treatment and 12 months after treatment

People with Down’s syndrome, Turner syndrome, Addison’s disease or other autoimmune diseases should also be tested regularly.

Some important points….

  • Blood tests are currently the most accurate way to diagnose and manage thyroid disorders
  • Your symptoms and how you feel are an important part of the diagnosis
  • It is important for your health that the TSH level is within the reference range
  • If you are taking medication for a thyroid disorder, there may be scope to fine-tune your treatment so that you feel better
  • If you have a diagnosed thyroid disorder or have had previous treatment for an over-active thyroid, it is important to have a blood test every 12 months, or as advised by your doctor
  • If you have a thyroid disorder you should have a blood test in early pregnancy or if you are planning a pregnancy
  • If you are taking medication, do not alter your dose without discussing this with your doctor

It is well recognised that thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.

If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.

The British Thyroid Foundation

The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

Endorsed by:

The British Thyroid Association – medical professionals encouraging the highest standards in patient care and research

The British Association of Endocrine and Thyroid Surgeons – the representative body of British surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)

First issued: 2008

Revised: 2011, 2015

Our literature is reviewed every two years and revised if necessary.

reference range

Универсальный англо-русский словарь . Академик.ру . 2011 .

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Physiological Changes In Pregnancy

Dr John Cox, 20 Jun 2016

Patient professional reference

Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use. You may find one of our health articles more useful.

In this article

  • arrow-downEndocrine system (non-reproductive) changes
  • arrow-downCardiovascular system changes
  • arrow-downRespiratory system changes
  • arrow-downAlimentary system changes
  • arrow-downUrinary tract changes
  • arrow-downHaematological changes
  • arrow-downMetabolic changes
  • arrow-downSkin changes
  • arrow-downMusculoskeletal changes
  • arrow-downInterpreting blood test results in pregnancy

Physiological Changes In Pregnancy

In this article

Pregnancy is associated with normal physiological changes that assist fetal survival as well as preparation for labour. It is important to know what ‘normal’ parameters of change are in order to diagnose and manage common medical problems of pregnancy, such as hypertension, gestational diabetes, anaemia and hyperthyroidism.

As a result of normal physiological change, normal ranges for certain blood tests are different in pregnancy, and women may have different susceptibility to medication. [1]

Endocrine system (non-reproductive) changes [2]

Pituitary hormones

  • FSH/LH fall to extremely low levels due to the high levels of oestrogen and progesterone.
  • ACTH and melanocyte-stimulating hormone increase.
  • Prolactin levels increase.
  • Pituitary growth hormone (GH) levels fall but overall serum levels increase due to placental production.
  • Oxytocin levels increase to a peak at term.
  • ADH levels are unchanged.

Thyroid and parathyroid gland

  • Thyroxine-binding globulin (TBG) concentrations rise due to increased oestrogen levels.
  • T4 and T3 increase over the first half of pregnancy but there is a normal to slightly decreased amount of free hormone due to increased TBG-binding. Normal ranges are slightly reduced in the second and third trimester.
  • TSH production is stimulated after the first trimester, although in healthy individuals this is not usually significant. A large rise in TSH is likely to indicate iodine deficiency or subclinical hypothyroidism.
  • Women are relatively iodine-deficient in pregnancy; the World Health Organization (WHO) recommends an increased intake during this time. [3, 4] Where iodised salt is unavailable, supplements are recommended. If iodine levels are maintained in pregnancy, the thyroid gland should stay the same size and any increase be investigated. It will be larger in the presence of iodine deficiency.
  • Although fetal need for calcium is high, maternal serum calcium levels are maintained in pregnancy by increased intestinal absorption. There is also increased excretion in the urine, as a result of which pregnant women are at increased risk of renal stones.
  • Colecalciferol (vitamin D3) is converted to its active metabolite, 1,25-dihydroxycolecalciferol, by placental 1α-hydroxylase. Serum levels rise and are responsible for the increased intestinal absorption of calcium.

Adrenal gland and pancreas

  • Cortisol levels increase in pregnancy, which favours lipogenesis and fat storage.
  • Insulin response also increases so blood sugar should remain normal or low.
  • Peripheral insulin resistance increases after early stages of pregnancy due to increased production of hormones such as cortisol, prolactin, progesterone and human placental lactogen.
  • The combination of insulin resistance and relatively low glucose promotes the use of fat for energy, preserving glucose and amino acids for the fetus.
  • Gestational diabetes is thought to reflect a pronounced insulin resistance of this sort.
  • HbA1c is not considered suitable for use in pregnancy, as normal range changes and suitable reference ranges have not been established. [5]

Cardiovascular system changes [2]

  • There is peripheral vasodilation.
  • Cardiac output increases by 20% by week 8, and then further up to 40% increase, maximal at week 20-28. In labour there is further increase in cardiac output and then a huge increase immediately after delivery, followed by return to normal within around an hour.
  • Contributing to the increased cardiac output are increased stroke volume and an increase in heart rate of 10-20 beats per minute.
  • Blood pressure is lower than normal in the first two trimesters but returns to normal in the third.
  • Venous return in the inferior vena cava can be compromised in late pregnancy if a woman lies flat on her back due to pressure from the uterus, resulting in reduced stroke volume and cardiac output. This is relieved by lying in the left lateral position. Reduced cardiac output can compromise fetal blood supply.
  • There is an increased risk of pulmonary oedema if there is an increase in blood volume, or increased pulmonary capillary permeability secondary to pre-eclampsia. The highest risk time is the second stage of labour or immediate postpartum period when cardiac output is high.
  • Changes on examination and ECG below are caused by the physiological changes described above.

Cardiac examination in pregnancy

  • There may be a bounding or collapsing pulse.
  • Many women have a third heart sound after mid-pregnancy.
  • Diastolic murmurs should be considered potentially pathological.
  • Systolic flow murmurs are common.

ECG changes considered normal in pregnancy

  • Left axis deviation.
  • Small Q waves and inverted T wave in lead III.
  • ST depression and inversion or flattening of the T wave in inferior and lateral leads.
  • Atrial and ventricular ectopics.

Respiratory system changes [2, 6]

  • Tidal volume increases by about 200 ml, increasing vital capacity and decreasing residual volume. In later stages of pregnancy, splinting of the diaphragm may occur with some decrease in tidal volume. Respiratory rate does not alter significantly.
  • Increased oxygen consumption (by approximately 20%) and increased metabolic rate cause increased oxygen demand.
  • State of compensated respiratory alkalosis – arterial pCO2 drops, arterial pO2 rises and decrease in bicarbonate prevents pH change. Lower maternal pCO2 facilitates oxygen/carbon dioxide transfer to/from the fetus.
  • Many women complain of feeling short of breath in pregnancy without hypoxia or explanatory pathology. The mechanism of this is not fully understood

Alimentary system changes

  • Nausea and vomiting are common in early pregnancy.
  • Appetite is usually increased, sometimes with specific cravings.
  • Progesterone causes relaxation of the lower oesophageal sphincter and increased reflux, making many women prone to heartburn. Pressure on the stomach from the enlarging uterus further contributes to this in later pregnancy.
  • Gastrointestinal motility is reduced and transit time is consequently longer. This allows increased nutrient absorption. Constipation is common.
  • The gallbladder may dilate and empty less completely. Pregnancy also predisposes to the precipitation of cholesterol gallstones.
  • Gums become spongy, friable and prone to bleeding. Good dental care is important.

Urinary tract changes [6]

  • The increased blood volume and cardiac output during pregnancy cause a 50-60% increase in renal blood flow and glomerular filtration rate (GFR). This causes an increased excretion and reduced blood levels of urea, creatinine, urate and bicarbonate.
  • Mild glycosuria and/or proteinuria may occur because the increase in GFR may exceed the ability of the renal tubules to reabsorb glucose and protein.
  • Increased water retention causes a reduction of plasma osmolality.
  • The smooth muscle of the renal pelvis and ureter become relaxed and dilated, kidneys increase in length and ureters become longer, more curved and with an increase in residual urine volume.
  • Bladder smooth muscle also relaxes, increasing capacity and risk of urinary tract infection.
  • The enlarging uterus may put pressure on the ureters.
  • 2-10% of women have asymptomatic bacteriuria in pregnancy and if untreated up to 30% may develop acute pyelonephritis. [7]

Haematological changes [2, 6]

  • Plasma volume increases over the course of pregnancy by about 50%. Dilutional anaemia is caused by the rise in plasma volume. Elevated erythropoietin levels increase the total red cell mass by the end of the second trimester but haemoglobin concentrations never reach pre-pregnancy levels.
  • Usually mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC) are unaffected.
  • A modest leukocytosis is observed.
  • A normal pregnancy creates a demand for about 1000 mg of additional iron. This equates to 60 mg elemental iron or 300 mg ferrous sulfate per day.
  • Serum iron falls during pregnancy whilst transferrin and total iron binding capacity rise.
  • Levels of some clotting factors (VII, VIII, IX and X) and fibrinogen increase whilst fibrinolytic activity decreases. These changes protect from haemorrhage at delivery but also make pregnancy a hypercoagulable state with increased risk of thromboembolism. See separate Venous Thromboembolism in Pregnancy article.
  • One study found that during early pregnancy: antithrombin activity remained unchanged, protein S activity decreased significantly and there was a potentially biologically significant increase in protein C activity. [8] See separate Thrombophilia article.
  • Serum albumin decreases.

Metabolic changes

  • The basal metabolic rate increases slowly over the course of pregnancy, by 15-20%.
  • It is thought that energy requirement does not increase significantly during the first or second trimesters, increasing by around 200 kcal per day in the third. [9]
  • Active energy expenditure tends to fall over pregnancy.
  • Recommended normal weight gain in pregnancy is 11.4 to 15.9 kg for a woman of normal body mass index (BMI). [10] Around 5 kg is the fetus, placenta, membranes and amniotic fluid and the rest is maternal stores of fat and protein and increased intra- and extra-vascular volume. Weight is no longer monitored in pregnancy as it does not affect outcome and is affected by a number of factors.

Skin changes

  • Hyperpigmentation of the umbilicus, nipples, abdominal midline (linea nigra) and face (melasma (chloasma)) are common due to the hormonal changes of pregnancy.
  • Hyperdynamic circulation and high levels of oestrogen may cause spider naevi and palmar erythema.
  • Striae gravidarum (‘stretch marks’) are common.

Musculoskeletal changes

  • Increased ligamental laxity caused by increased levels of relaxin contribute to back pain and pubic symphysis dysfunction.
  • Shift in posture with exaggerated lumbar lordosis leading to the typical gait of late pregnancy.

Interpreting blood test results in pregnancy [11]


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