Hemodynamic Changes

In addition to sodium retention, water retention is also a key pregnancy-induced change. Plasma osmolality decreases as early as 5 wk (14). The relative hypotonicity of the plasma is maintained by an approx 10 mosmol kg decrease in the osmotic threshold for both thirst and vasopressin (antidiuretic hormone) release. Lowering the threshold to drink stimulates water intake and dilution of body fluids. Vasopressin is not suppressed at the usual osmolality, therefore, it continues to circulate and...

Combining Multiple Markers Into a Risk Based Screen

As a marker for risk of Down syndrome, MSAFP by itself measured solely for the purpose of estimating the risk of Down syndrome would not be powerful enough to be justified. However, because MSAFP is widely used for ONTD screening, use of its modest additional information about the risk of Down syndrome is easily justified. Screening for Down syndrome also benefited from screening for ONTD in that the concept of the MoM had already been developed for ONTD screening (see Using the MoM to Adjust...

Confounding Variables of Second Trimester Markers and Risk

Similar to prenatal screening for ONTD, there are a number of factors that modify the risk of Down syndrome from that derived from the maternal age and optimally measured marker concentrations. MSuE3 concentrations increase by approx 25 per wk through the early second trimester (Fig. 10), although this rate of rise diminishes slightly beyond week 18 (143). In contrast, maternal serum (MShCG) concentrations decrease from their 10-12 wk maximum, most rapidly during weeks 15-17, reaching...

Cervical Ultrasound

The cervix changes throughout gestation, with the most dramatic changes occurring soon before delivery. The cervix shortens, softens, takes a more anterior position, and finally begins to dilate (5). Although digital exams are used to assess these cervical changes and to stratify which patients are at high risk for preterm delivery, manual cervical examinations by clinicians are subject to significant variation between observers, making digital exams of questionable accuracy and reproducibility...

Clinical Aspects of Trisomy 21 Down Syndrome

A congenital syndrome of mental retardation associated with specific facial and physical features was first described by J. Langdon Down in 1866 ( 72). Down syndrome is characterized by a moderate to severe learning disability (average IQ approx 40) and congenital heart defects affecting approx 50 of affected individuals. The birth prevalence of Down syndrome ranges from approx 1 in 800 up to 1 in 400, depending on the maternal age distribution of pregnant women in the region. Down syndrome is...

The Integrated Test Combining First and Second Trimester Markers

If first-trimester screening relies on the nondisclosure of the ultrasound results until the first-trimester biochemical markers become available, could screening be further improved by waiting even longer for the second-trimester markers to become available A screening method called the Integrated Test, first proposed by Wald et al. in 1999, utilizes the potential of both first- and second-trimester screening markers (263). The term integrated stems from the concept of combining information...

Info

MSAFP distributions in twin pregnancies, expressed in MoM for unaffected singleton pregnancy. Despite the greater overlap between the unaffected and affected (one twin) pregnancies, a moderately successful OSB screen can be performed. Twin Pregnancies. Large-scale studies of MSAFP in twin pregnancies have generated sufficient data to construct the frequency distribution of MSAFP in OSB as well as in unaffected twin pregnancies (47,48,56). The distributions are log Gaussian, like their...

Calculating Patient Specific Risks of the Targeted Disorder

With knowledge of the relative frequency distributions of the affected and unaffected populations for a given screening variable (e.g., MSAFP MoM result, see Fig. 3), the risk of the targeted disorder can be calculated from the screening variable result. Although screening for ONTD initially used a MoM cutoff value, as patients become more informed participants in their health care decisions, the pattern of practice is shifting to reporting both the MoM value and its associated patient-specific...

Biology of Second Trimester Serum Biochemical Markers for Down Syndrome

Trisomy Afp

The pathophysiological basis of Down syndrome is unknown, although the sequence of chromosome 21 has now been completed 120 . Similarly, the reasons for altered second-trimester maternal serum analytes in Down syndrome pregnancy remain largely unexplained. A current hypothesis for the second trimester is that the serum analyte pattern is related to poorly functioning fetal tissue with compensatory placental hyper-function. The mechanisms leading to this phenomenon of increased placental and...

Is Louis Gluck Founded The Ls Ratio

Marie Kulovich and Louis Gluck developed the L S ratio in the early 1970s 72,73 . The major component of AF lecithin is dipalmitoyl PC, the best biologically derived surfactant. Sphingomyelin has no pulmonary surfactant role and therefore serves as a convenient internal control. Kulovich and Gluck expanded the technique to include PG and PI by two-dimensional chromatography and called this procedure the lung profile 74,75 . In 2002, only 18 laboratories perform the lung profile 20 . Because...

Hepatic System

The size and histology of the liver is largely unchanged during pregnancy. Absolute blood flow through the liver is also unchanged. Therefore, because cardiac output increases, the liver actually receives a smaller percentage of the total cardiac output 10 . The relative decrease in blood volume through the liver, combined with the increase in volume of distribution, may affect the clearance of some drugs during pregnancy. Liver function tests are frequently misinterpreted in normal pregnancy...

Respiratory System

Relative hyperventilation occurs during the luteal phase of the menstrual cycle, resulting from the presence of progesterone. This causes alveolar and arterial tensions of carbon dioxide to fall. When pregnancy is established, the hyperventilation continues and by term, end-tidal partial pressure carbon dioxide PCO2 and arterial PCO2 decline to below 30 torr 14,33 . The magnitude of this decrease is proportional to progesterone concentrations 14 . The mechanism by which progesterone causes...

91011121314

Relative changes in the median free -hCG and PAPP-A concentrations in maternal serum during the first trimester of pregnancy. Fig. 14. Maternal serum PAPP-A distributions during the 10th wk of gestation in the Down syndrome and unaffected populations. The LR for the PAPP-A MoM values is shown, with the scale of LR values on the right of the figure. Fig. 14. Maternal serum PAPP-A distributions during the 10th wk of gestation in the Down syndrome and unaffected populations. The LR for...

Trisomy

Trisomy 18 Edwards' syndrome T18 is less common and more lethal than trisomy 21. The prevalence of T18 during the first and second trimester is approx 1 in 3000 but spontaneous loss of T18 pregnancies reduces the birth prevalence to approx 1 in 8000. T18 pregnancies miscarry at a rate of 70 between midpregnancy and term 264,265 . Like Down syndrome, the prevalence of T18 is correlated with increasing maternal age. T18 is characterized by severe mental retardation, growth retardation, and...

Preface

During pregnancy, a woman undergoes a multitude of normal physiological changes and is subject to a variety of pregnancy-specific diseases. Furthermore, there are a number of diseases that can affect the unborn fetus and the physiological status of the fetus can in turn affect the mother. Taken together, laboratory testing during pregnancy can be complicated and confusing. The aim of Handbook of Clinical Laboratory Testing During Pregnancy is to aid clinicians and laboratorians in the art of...

TDx FLM II

The first-generation test, TDx FLM, was developed by Russell 39 at Abbott Laboratories, Inc., in collaboration with Tait et al. 40 as an attempt to improve on the original work of Shinitzky and colleagues 41 . The original Shinitzky method used diphenyl-hexatriene DPH and an ultraviolet fluorescence spectrophometer. The results were reported in polarization units. Because DPH is very unstable and the instrument was difficult to maintain, this method never achieved widespread use. Tait's method...

Diagnostic Tests for Ontd Afafp and AChE

The most accurate diagnosis of ONTD requires amniocentesis with measurement of AF AFP and AChE 24,70 . Both of these tests are diagnostic of ONTD, and the existence of two such tests allows for their selected combined application to maximize diagnostic performance. Abnormal AFAFP results are usually defined as greater than 2.0 MoM. In these patients, AChE can add to the diagnostic certainty and reduce false positives to a dramatically low level. AChE can also be performed when a positive family...

Confounding Variables Influencing AFP Concentration

Normal Pregnancy

Relative changes in the median AFP values in maternal serum and AF at each week during the early second trimester of pregnancy. 14 15 16 17 18 19 20 21 22 Gestational Weeks Fig. 4. Relative changes in the median AFP values in maternal serum and AF at each week during the early second trimester of pregnancy. per week Fig. 4 . In order to eliminate the need to have normative data for each week of gestation, patient results are expressed as the ratio of the median concentration in...

Interassay Variation

Nicked Hcg

Interassay variation between different quantitative serum tests and between different qualitative urine tests can cause confusion and misdiagnosis of pregnancy. Most clinical laboratories participate in external proficiency testing through the College of American Pathologists CAP . CAP surveys have been the biggest indicator of interassay variation. The five most recent CAP surveys each with a single hCG preparation of 2307 to 2324 testing laboratories showed 1.50- to 1.59-fold variations from...

References

Time of implantation of the conceptus and loss of pregnancy. N Engl J Med 1999 340 1796-1799. 2. Wilcox AJ, Baird DD, Dunson D, McChesney R, Weinberg CR. Natural limits of pregnancy testing in relation to the expected menstrual period. JAMA 2001 286 1759-1761. 3. Daya S. Human chorionic gonadotropin increase in normal early pregnancy. Am J Obstet Gynecol 1987 156 286-290. 4. Pittaway DE, Reish RL, Wentz AC. Doubling times of human chorionic gonadotropin...

Introduction

Human Chorionic Gonadotropin Nicked

Human chorionic gonadotropin hCG is a glycoprotein composed of two dissimilar subunits, a- and P-subunit, held together by charge interactions. hCG is produced by trophoblastic cells of the placenta in both pregnancy and gestational trophoblastic diseases. It is a remarkable glycoprotein in that up to 35 of the molecular weight MW is from oligosaccharide side chains. hCG is sometimes considered a mucopolysaccharide, like collagen, because of the large carbohydrate component. There is wide...

Endocrine Changes And Metabolic Adaptations

Macrosomia Fetal

Gestation is associated with profound hormonal and metabolic changes in the mother. These changes are responsible for establishing and maintaining pregnancy, fetal growth and development, and subsequent lactation. The first endocrine changes of pregnancy can be detected as early as 1 wk after ovulation. During the luteal phase of the menstrual cycle, the corpus luteum CL produces progesterone and estrogen for approx 12-14 d. Progesterone is required to maintain pregnancy. If fertilization...

Amniotic Fluid

Amniotic fluid is a body fluid that is unique to pregnancy. The volume of amniotic fluid increases progressively through gestation until approx 34 wk, when the volume begins to decrease. It is approx 200 to 300 mL at 16 wk, 400 to 1400 mL at 26 wk, 300 to 2000 mL at 34 wk, and 300 to 1400 mL at 40 wk 35 . The volume of amniotic fluid at term is approx 800 mL and constitutes only 6 of the total maternal weight gain by fluids 27 Table 7 . During gestation, a woman with a single fetus will gain,...

Contributors

Adewale Adeyinka, mbbs, PhD Cytogenetics Laboratory, Mayo Clinic and Mayo Foundation, Rochester, MN Edward R. Ashwood, md ARUP Laboratories, University of Utah School of Medicine, Salt Lake City, UT William A. Bennett, PhD Department of Obstetrics and Gynecology, University of Mississippi Medical Center, Jackson , MS Isaac Blickstein, md Department of Obstetrics and Gynecology, Kaplan Medical Center, Rehovot and the Hadassah-Hebrew University School of Medicine, Jerusalem, Israel Lynn Bry, md,...