| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Technical Briefs |
1
Ist. di Chim. e Chim. Clin. and
2
Clin. Ostet. e Ginecol., Univ. Cattolica del S. Cuore, Facoltà di Med. e Chirurg. "A. Gemelli", Largo Francesco Vito 1, 00168 Roma, Italy;
a author for correspondence: fax 039-6-35501918, e-mail b.giardina{at}uniserv.ccr.rm.cnr.it
The intrauterine biochemical assessment of the human fetus is important in fetal medicine, for both prenatal diagnosis and therapy of fetal diseases. Percutaneous umbilical blood sampling (PUBS) performed with ultrasound guidance is reliable for this, and the microvolume specimens obtained by this technique are readily analyzed by modern clinical chemistry analyzers to perform complete biochemical profiles with small blood volumes.
The interpretation of fetal biochemical tests requires age-gestational specific reference intervals to reveal possible pathological processes and to minimize the remarkable physiological variability observed with fetal growth and maturation, particularly in the last trimester of gestation. Various cord blood analytes have been investigated as potential indicators of fetal distress (1)(2), but no comprehensive report of reference intervals adjusted to various weeks of gestation has been available. Here, we present reference intervals for 18 analytes in plasma samples obtained by PUBS from 72 healthy fetuses between weeks 18 and 40 of pregnancy.
We analyzed plasma from 171 fetuses who underwent PUBS between the 18th and 40th week of gestation for various indications (Rh alloimmunization 79, maternal viral or parasitic infection 42, rapid karyotyping 25, and maternal thrombocytopenia 25). Informed consent was obtained from the parents. Gestational age at the time of sampling was determined from menstrual dates or by ultrasonography when the dates were uncertain. We selected 72 fetuses as "healthy" when the suspected pathologies were not confirmed and the subsequent progress of the pregnancy revealed no abnormalities; further, these babies were confirmed healthy at birth by pediatric examination and laboratory screening.
All fetal blood samplings were performed manually with ultrasound guidance by a single operator with heparin-coated 20-gauge needle, after abdominal infiltration with a local anesthetic. The ultrasound evaluation allows determination of where the placenta is located and the site of insertion. When the site of umbilical insertion was difficult to isolate and identify, a free standing loop of umbilical cord was utilized (3). Cardiotocogram monitoring was performed before and after every procedure to exclude fetal behavioral abnormalities resulting from the PUBS. Each fetus was sampled only once during the pregnancy.
All biochemical tests were performed within 2 h after the specimen
was collected in a tube containing liquid lithium-heparin (LP spa), and
all samples were stored at 4 °C until analysis. Plasma samples were
analyzed with a Hitachi 717 automated analyzer (Boehringer Mannheim)
and using the manufacturer's calibrators and reagents except in the
assays of glucose, urea, cholesterol, 
-glutamyltransferase
(SGM), calcium (Penta), alkaline phosphatase (ALKP; Randox), and
creatine kinase (CK; Sigma).
The reference interval for each analyte was determined by nonparametric statistical analysis according to the recommendations of the IFCC (4). Outliers, if present, were eliminated by visual inspection of frequency distributions. The reference intervals in use in our laboratory for adults and infants were calculated nonparametrically from results for 300 and 200 healthy subjects, respectively, according to the IFCC recommendations (4).
Production of reliable reference intervals requires careful selection of "reference individuals" (to be representative of the healthy population), careful collection and storage of specimens under defined conditions, control of analytical variation during the period of the analyses, and, finally, correct statistical treatment of the results obtained. In fulfilling these requirements, we followed the guidelines recommended by the IFCC (4).
We chose to select the "fetal reference individuals" retrospectively; philosophical and ethical considerations made a priori selection impossible. In fact, defining a healthy state in fetuses is more difficult than in adults because PUBS is executed during gestation only on the basis of specific anamnestic and clinical suggestions.
The low number of samples obtained in some gestation weeks did not
allow us to calculate the age-gestational-specific reference intervals
that would be more representative of biochemical changes occurring
during fetal life. We considered stable those variables that did not
show a significant correlation with gestational age (P
>0.05). For these analytes we considered it valid to use the results
obtained during the whole gestational period for calculation of the
reference intervals (Table 1
).
|
The behavior of those analytes that change with gestational age (P <0.05) is shown in Fig. 1. As reported also by Weiner et al. (5) and Takagi et al. (6), total protein and albumin concentrations in plasma tend to increase with advancing fetal age but are consistently lower than that of adults. Similar positive trends are shown by the enzymatic activities of CK and acylcholine-acylhydrolase (CHE II), whereas the enzymatic activity of ALKP decreases after the peak between the 21th and 25th weeks, as reported also by Legras et al. (7). In the last weeks of pregnancy, the enzymatic activities of CK and CHE II fall to within the reference interval for infants, whereas that of ALKP is much lower.
Frequency distributions were of the gaussian type only for glucose, calcium, chloride, and uric acid—as demonstrated by the kurtosis and skewness coefficients and by the Kolmogorov–Smirnov test.
The fetal reference intervals for sodium, potassium, urea nitrogen, creatinine, lactate dehydrogenase, uric acid, and magnesium are very close to those of infants. For glucose, aspartate aminotransferase, alanine aminotransferase, cholesterol, and triglycerides, the fetal reference intervals are shifted to much below those of adults. The fetal reference interval for total bilirubin is lower than that of infants but higher than that of adults.
The lower limit of the fetal reference interval for calcium was below
that of adults, but the upper limits of the fetal reference interval
for chloride, inorganic phosphorus, and direct bilirubin were higher.
The interval for enzymatic activity of -glutamyltransferase was
higher than that in both infants and adults.
Recently, Perkins et al. (8) reported reference intervals
for 21 clinical chemistry analytes determined in plasma obtained from
arterial and venous umbilical cord blood from healthy term infants
after delivery but before placental expulsion. Except for K, Ca, P, Cl,
uric acid, and -glutamyltransferase enzymatic activity, our findings
are similar to those they reported for healthy term infants. We are not
able to fully explain these differences; presumably they are related to
the different size and composition of the fetal reference
populations, given that our adult reference intervals are closely
similar to those of Perkins et al.
In conclusion the analysis of our data obtained for 18 analytes suggests that the fetal reference intervals are similar to those of infants only for urea nitrogen, Na, K, creatinine, lactate dehydrogenase, uric acid, and Mg. For those analytes that change as a function of gestational age, knowledge of the fetal reference intervals according to stage of pregnancy is important, particularly when therapy is necessary (e.g., albumin infusions in nonimmune hydrops).
|
References
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
