Alpha-fetoprotein levels in amniotic fluid in pregnancies complicated by rhesus isoimmunization

Maternal serum alpha-fetoprotein, fetal middle cerebral artery blood flow velocity and fetal haemoglobin in pregnancies at risk of fetal anaemia

OBJECTIVES

To evaluate the relationships between maternal serum alpha-fetoprotein (MSAFP) levels and both middle cerebral artery (MCA) peak systolic velocity and fetal haemoglobin in women at risk of fetal anaemia.

METHODS

Forty-one measurements of MSAFP were carried out in 22 women at risk of fetal anaemia (16 alloimmunised patients and 6 cases of parvovirus infection) who were monitored by using MCA Doppler measurements. The relationships between MSAFP (MoM) and both MCA peak systolic velocity (z-scores) and fetal haemoglobin (MoM) were studied.

RESULTS

There were significant correlations between MSAFP and both MCA Doppler measurements (r = 0.56, p = 0.00017) and fetal haemoglobin (n = 13, r = -0.71, p = 0.006). MSAFP was higher in cases with fetal anaemia (n = 10) than in those with normal haemoglobin levels (n = 3) (1.7 +/- 0.4 vs 0.8 +/- 0.1 MoM; p = 0.006). In cases of alloimmunised pregnancies with fetal anaemia, MSAFP elevations preceded the presence of increased MCA Doppler velocity by 2.7 weeks (range 0-9 weeks).

CONCLUSION

MSAFP is significantly correlated with both MCA Doppler measurements and fetal haemoglobin. Elevations of MSAFP may appear earlier than MCA Doppler abnormalities in cases of fetal anaemia associated with red blood cell alloimmunisation.

Fetal serum alpha-fetoprotein in alloimmunised pregnancies

OBJECTIVES

Maternal serum alpha-fetoprotein (AFP) levels have been known to be increased in red blood cell alloimmunisation. Since AFP is now thought be a pro-erythropoietic factor, we wished to evaluate fetal serum levels of AFP in cases of alloimmunised pregnancies.

METHODS

We studied AFP levels in 32 fetal serum samples from women with red blood cell alloimmunisation at the time of the first fetal blood sampling. We expressed the levels of AFP and haemoglobin as absolute numbers and as delta values (number of SDs by which the observed value differed from the normal mean for the same gestation). Main outcome measures were fetal serum AFP levels and fetal haemoglobin concentration.

RESULTS

Overall, fetal AFP level was higher than normal in the cases (delta values 2.4 +/- 5.5 SD). However, mildly affected non-hydropic cases had higher levels than severely affected fetuses with hydrops.

CONCLUSIONS

Fetuses affected by red blood cell alloimmunisation have increased levels of serum AFP but these levels fall back to low levels in severe anaemia especially with hydrops, which could represent the failing of a compensatory erythropoietic mechanism. Our results suggest that fetal haematopoiesis is activated early in red blood cell alloimmunisation but was subsequently impaired.

Alpha 1-fetoprotein (AFP) reference values in infants up to 2 years of age

The aim of this study was to establish reference values and factors associated with serum AFP elevation in infants. Five hundred twenty-four samples collected from infants up to the age of 2 years at the University Hospital Düsseldorf (Germany) were analyzed. At birth mean serum AFP levels were 41,687 ng/ml in 256 term babies and 158,125 ng/ml in 90 premature babies born before the 37th gestational week, excluding samples from children with factors known to be associated with AFP elevation. In the first 4 weeks of life, AFP levels decreased by 50% in 5.1 days in term babies. Between day 180 and 720 of life, AFP levels up to 87 ng/ml were within the 95.5% interval (assumed logarithmic normal distribution) with a mean of 8 ng/ml without a further decline. By the age of 2 years the infants of this study had not reached adult serum AFP levels (0-6 ng/ml).

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.

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.