INTRODUCTION — Numerous physiologic changes occur during pregnancy to accommodate the maternal and fetal needs. Most of these changes begin soon after conception and continue until late gestation. Not surprisingly, these physiologic adaptations of pregnancy result in many significant changes in laboratory test values. Some of these changes are well-known, such as the reduction in hematocrit and hemoglobin levels, which is termed physiologic or dilutional anemia of pregnancy. Similarly, the renal changes leading to lower creatinine values in pregnancy are well-described and a "normal" serum creatinine value of 1.0 mg/dL in a nonpregnant female is immediately recognized as elevated in pregnancy.
Despite the well-recognized phenomenon of pregnancy-induced physiologic changes and their potential for altering normal laboratory values, very few laboratories provide clinicians with normal reference ranges during pregnancy. Indeed, many laboratories do not even report normal values for females versus males. This topic will discuss normal reference ranges for laboratory values during pregnancy based upon our review of the literature [1-75].
NORMAL REFERENCE RANGES IN PREGNANCY — Previous investigators have compiled information on normal laboratory reference ranges in pregnancy [30,40,43,76]. Using these references, as well as publications by other researchers in which normal values were determined across pregnancy for a number of analytes, we compiled a table of the most common, and some not so common, laboratory test values across pregnancy (table 1) [1-75].
Laboratory test values are grouped by system and listed for each trimester and for nonpregnant adults. The table shows that some analytes, such as the leukocyte count and alkaline phosphatase levels, continue to rise during normal pregnancy. Similarly, the upper limit of normal for D-dimer nearly doubles during midpregnancy. Several hormones and coagulation factors all increase markedly. Unless these normal, pregnancy-related alterations are taken into account when evaluating laboratory values in a pregnant patient, many of the physiologic adaptations of pregnancy can be misinterpreted as pathologic or may mask diagnosis of a disease process.
We consider these data the best available information on normal reference ranges in pregnancy; however, there are some limitations. The analysis is subject to the inherent limitations of abridged data and does not account for potential variations between racial groups, regions of the world, and time of day of sampling. Although we have tried to include comparisons of analytes performed by similar analytic methods, some variation is inevitable. In the majority of instances, reference ranges for analytes are expressed as 5th to 95th percentiles, but some are reported with standard deviations. In addition, pregnancy-specific information is not always available for laboratory tests that have been newly introduced into medical care or have recently gained in popularity. Despite these limitations, the table is intended to provide a quick reference for most laboratory values needed to provide care for the pregnant patient.
ADDITIONAL RESOURCES — Additional information on physiologic changes during pregnancy can be found in the following UpToDate topic reviews:
●(See "Maternal adaptations to pregnancy: Dyspnea and other physiologic respiratory changes", section on 'Physiologic cardiopulmonary changes in pregnancy'.)
●(See "Maternal adaptations to pregnancy: Hematologic changes".)
●(See "Maternal adaptations to pregnancy: Cardiovascular and hemodynamic changes".)
●(See "Maternal adaptations to pregnancy: Gastrointestinal tract".)
●(See "Maternal adaptations to pregnancy: Musculoskeletal changes and pain".)
●(See "Maternal adaptations to pregnancy: Skin and related structures".)
●(See "Maternal adaptations to pregnancy: Renal and urinary tract physiology".)
●(See "Clinical manifestations and diagnosis of early pregnancy".)
●(See "Immunology of the maternal-fetal interface".)
SUMMARY AND RECOMMENDATIONS
●Laboratory test values across pregnancy – Numerous physiologic changes occur during pregnancy to accommodate the maternal and fetal needs. This table shows common, and not so common, laboratory test values across pregnancy (table 1). (See 'Normal reference ranges in pregnancy' above.)
1 : Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum.
4 : Calcium-regulating hormones and parathyroid hormone-related peptide in normal human pregnancy and postpartum: a longitudinal study.
6 : Liver function tests in normal pregnancy: a prospective study of 103 pregnant women and 103 matched controls.
10 : Fluctuations in C-reactive protein concentration and neutrophil activation during normal human pregnancy.
11 : Serum levels of erythropoietin and soluble transferrin receptor in the course of pregnancy in non beta thalassemic and beta thalassemic women.
12 : Relationship of systemic hemodynamics, left ventricular structure and function, and plasma natriuretic peptide concentrations during pregnancy complicated by preeclampsia.
13 : Relationship of systemic hemodynamics, left ventricular structure and function, and plasma natriuretic peptide concentrations during pregnancy complicated by preeclampsia.
16 : Coagulation and fibrinolysis changes in normal pregnancy. Increased levels of procoagulants and reduced levels of inhibitors during pregnancy induce a hypercoagulable state, combined with a reactive fibrinolysis.
17 : Tissue plasminogen activator levels change with plasma fibrinogen concentrations during pregnancy.
18 : Plasma osmolality and urinary concentration and dilution during and after pregnancy: evidence that lateral recumbency inhibits maximal urinary concentrating ability.
19 : Correlation of hormones with lipid and lipoprotein levels during normal pregnancy and postpartum.
21 : Renin, aldosterone, and serum-converting enzyme activity during normal and hypertensive pregnancy.
23 : Non-postural serial changes in renal function during the third trimester of normal human pregnancy.
31 : The changes of trace elements, malondialdehyde levels and superoxide dismutase activities in pregnancy with or without preeclampsia.
32 : Longitudinal study of plasma lipids and lipoprotein cholesterol in normal pregnancy and puerperium.
35 : The relationship between aldosterone to renin ratio and RI value of the uterine artery in the preeclamptic patient vs. normal pregnancy.
45 : Assessment of copper status in pregnancy by means of determining the specific oxidase activity of ceruloplasmin.
46 : Reference intervals for haematological variables during normal pregnancy and postpartum in 434 healthy Danish women.
47 : Erythrocyte folate, plasma folate and plasma homocysteine during normal pregnancy and postpartum: a longitudinal study comprising 404 Danish women.
48 : Serum erythropoietin during normal pregnancy: relationship to hemoglobin and iron status markers and impact of iron supplementation in a longitudinal, placebo-controlled study on 118 women.
49 : Parathyroid hormone and calcitriol changes in normal and insulin-dependent diabetic pregnancies.
50 : Longitudinal study of plasma lipoproteins and hormones during pregnancy in normal and diabetic women.
52 : Establishing a normal range for D-dimer levels through pregnancy to aid in the diagnosis of pulmonary embolism and deep vein thrombosis.
54 : Effect of smoking on serum concentrations of total homocysteine, folate, vitamin B12, and nitric oxide in pregnancy: a preliminary study.
62 : Relationship between urinary albumin and albumin/creatinine ratio during normal pregnancy and pre-eclampsia.
63 : Iron requirement in normal pregnancy as assessed by serum ferritin, serum transferrin saturation and erythrocyte protoporphyrin determinations.
65 : Comparison of blood levels of histamine and total ascorbic acid in pre-eclampsia with normal pregnancy.
70 : Assessment of adrenal reserve in pregnancy: defining the normal response to the adrenocorticotropin stimulation test.
71 : Haematological and biochemical profile of uncomplicated pregnancy in nulliparous women; a longitudinal study.
74 : Reference intervals for plasma levels of fibronectin, von Willebrand factor, free protein S and antithrombin during third-trimester pregnancy.
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