Alpha-fetoprotein in antenatal diagnosis

Retinol binding protein 4: an adipokine associated with intra-amniotic infection/inflammation

OBJECTIVE

Retinol binding protein 4 (RBP4), a specific carrier for retinol in the blood, is a novel adipokine that has been implicated in the pathophysiology of insulin resistance, and its gene expression has been associated with adipose tissue inflammation. Recently, proteomic profiling of amniotic fluid (AF) from women with preterm labor (PTL) revealed over-expression of RBP4 in those who delivered preterm. The aim of this study was to determine whether RBP4 is present in AF, and if its concentrations change with gestational age, in the presence of labor, and intra-amniotic infection/inflammation (IAI) in patients with spontaneous PTL.

STUDY DESIGN

This cross-sectional study included pregnant women in the following groups: (1) mid-trimester (n = 30); (2) term not in labor (n = 31); (3) term in labor (n = 30); (4) spontaneous PTL without IAI who delivered at term (n = 60); (5) PTL without IAI who delivered preterm (n = 64); and (6) PTL with IAI (n = 56). RBP4 concentrations in AF were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

(1) RBP4 was detected in all AF samples; (2) among patients with PTL, women with IAI had a higher median AF RBP4 concentration than those without IAI who delivered preterm (1268.9 ng/ml, interquartile range (IQR) 900.3-1970.1 vs. 815.8 ng/ml, IQR 592.4-1098.1; p < 0.001) and at term (828.7 ng/ml, IQR 499.7-1119.6; p < 0.001); (3) the median AF RBP4 concentration was higher in women in the mid-trimester than in those at term not in labor (1861.1 ng/ml, IQR 1486.2-2034.3 vs. 766.1 ng/ml, IQR 608.5-1154.1; p < 0.0001; (4) the median AF RBP4 concentration did not differ significantly between patients with PTL without IAI who delivered preterm and those who delivered at term (p = 0.7); and (5) among women at term, the median AF RBP4 concentrations was not significantly different between those in labor and those not in labor (p = 0.4).

CONCLUSIONS

RBP4 is a physiologic constituent of the AF. Among patients with PTL, the median AF concentration of immunoreactive RBP4 is elevated in pregnancies complicated by IAI. These results suggest that RBP4 may participate in the host response against IAI.

Alpha-fetoprotein: a review

Alpha fetoprotein (AFP) is the major protein of fetal serum and most resembles albumen, which replaces it shortly after birth. It is produced by fetal liver and passes into the amniotic fluid (AF) via fetal urine. A small amount crosses the membranes into the maternal circulation. Excluding fetal blood contamination, elevated AF/AFP levels indicate fetal demise or one of several abnormalities. Maternal serum (MS) AFP measurement can be used as a screening procedure to identify neural tube defects providing a rigorous protocol is followed. This requires that a laboratory establish its normal range of MS/AFP levels between 15 and 20 weeks gestation, employ a reliable assay with adequate controls, and has recourse to genetic counseling as well as expert sonography, amniocentesis and amniography if necessary. Pregnancy is the only normal situation in which AFP is present after birth. It may be present in high levels in certain malignancies and has been useful in monitoring their recurrence. This article will review the history, biochemistry, and different assays of AFP in AF and blood as well as the indications and limitations for their use.

Early prenatal diagnosis of neural-tube defects by ultrasound-guided fetoscopy

In three fetuses with neural-tube defects (N.T.D.s) the lesions were clearly seen by fetoscopy in the second trimester. In a fourth fetus, in which the diagnosis of N.T.D. was suspected because of raised amniotic-fluid alpha-fetoprotein, spina bifida was excluded by fetoscopic examination and a normal baby was delivered at term. Ultrasound-guided fetoscopy has a place in the diagnosis of N.T.D.s when the results of other investigations are conflicting or inconclusive, and may be useful in assessing the severity of a lesion.

The use of alpha fetoprotein in prenatal diagnosis

Maternal or blood levels of alpha fetal protein are elevated in the presence of certain fetal anomalies, particularly those of the neural tube in which protein from the cerebrospinal fluid may leak into the amniotic fluid. Since this is a nonspecific elevation, other diseases are potentially screened for by this determination. Alpha fetal protein levels should be measured on any amniotic fluid samples obtained during the middle trimester of pregnancy.

Radioimmunoassay of serum alpha-fetoprotein in patients with different maliganant tumors

The level of serum alpha-fetoprotein (AFP) was estimated by radioimmunoassay in 153 normal healthy Malysians of different ethnic groups. The mean level was 7.5 In1/ml (SD 2.28InU/ml). Among 330 patients with malignant tumors, 11 had increased levels of AFP. The only patient who had hepatoma had a very high level of serum AFP. High levels were also found in three of four patients with dysgerminoma of the ovary, in the only two patients with carcinoma of the testis, and in one patient with secondary carcinoma of the humerus of unknown origin. Lower, but significantly increased levels were observed in one patient (of 48) with breast carcinoma, one patient (of 8) with basal cell carcinoma of the nose, one patient (0f 27) with carcinoma of the lung, and one patient (of 59) with nasopharynegeal carcinoma.

Alpha-fetoprotein

Despite all the information about AFP presented, a great deal still needs to be discovered especially in pregnancy. Geographical and racial differences remain to be elucidated. Similarly, differences in obstetric population in Helsinki and Baltimore, for example, are only now being studied. Sex differences may exist; Lardinois and associates195 cited a higher level of AFP in male than female fetuses. The important questions that need to be answered are whether AFP assays can help improve the other half of prenatal care- that directed to the fetus- and whether the AFP model can help enhance our understanding of the similarities and differences of fetal and cancer cells.

The present status of prenatal detection of neural tube defects

In experimentally induced myelocele in rats, efforts to find neural cells in amniotic fluid (AF) were unsuccessful. Creatine phosphokinase (CPK) and aldolase concentrations studied in serum of 118 and cerebrospinal fluid (CSF) in 9 patients with myelomeningocele showed serum CPK to be significantly elevated and more responsive to additional muscle injury than aldolase, but both enzymes appeared in lower concentrations in patients with myelomeningocele than those with infantile atrophy or cerebral palsy. In CSF, CPK, and aldolase concentrations averaged 4.2 I.U. and 2.7 S.L.U. per milliliter, respectively. Significant CPK elevation (p less than 0.001) was also found in AF from myeloschitic fetuses and maternal rat serum. Although these findings suggest that increased CPK concentration is an indicator of myelocele in rats, the technique is impractical for prenatal detection of human fetus occurs too late in gestation. This does not, however, preclude the value of CPK for detecting onset of paraparesis. In all myeloschitic human fetuses, the CSF communicates directly with AF for at least 3 to 4 weeks. This implies that CSF is probably the principal source of increased alpha-fetoprotein concentration encountered in AF of all pregnancies with NTD. When biological variables are recognized, it is evident that increased concentration of amniotic fluid alpha fetoprotein is a reliable indicator of fetuses with open myelocele and/or anenciphalus.

Amniotic fluid alphafetoprotein measurements in the early prenatal diagnosis of central nervous system disorders

Amniotic fluid alphafetoprotein (AFP) has been measured in 520 pregnancies between 8 and 24 weeks of gestation. The normal range of values has been defined for fortnightly periods between these limits. Grossly elevated AFP concentrations were found in four pregnancies leading to spina bifida and nine pregnancies leading to anencephaly. Slightly elevated AFP concentrations were found in one twin pregnancy and two pregnancies affected by rhesus isoimmunisation. Normal AFP values were observed in 36 amniotic fluids from pregnancies where the outcome was rhesus isoimmunisation, an inborn error of metabolism, a cytogenetic disorder or a birth defect unrelated to the central nervous system. The reliability of amniotic fluid AFP in the early prenatal diagnosis of spina bifida and anencephaly and the possibility of performing assays on samples sent by post from any part of the world are emphasized.