M. J. Kitau

MATERNAL PLASMA ALPHAFETOPROTEIN LEVELS IN THE SECOND HALF OF NORMAL PREGNANCY: RELATIONSHIP TO FETAL WEIGHT, AND MATERNAL AGE AND PARITY

A semi‐automated radioimmunoassay for plasma alphafetoprotein has been developed, suitable for routine clinical use. Several hundred samples can be assayed in a working week, with results available within 24 hours. The use of extensive quality controls ensures that good precision is maintained both within and between assays. The range of plasma concentrations of alphafetoprotein in the second half of pregnancy has been established in 100 normal subjects. The levels rise progressively to reach a peak at 32 weeks, and thereafter fall until term. No relationship between circulating alphafetoprotein levels and birth weight was observed.

ALPHA-FETOPROTEIN LEVELS IN PREGNANCIES COMPLICATEED BY GASTROINTESTINAL ABNORMALITIES OF THE FETUS

Alpha‐fetoprotein (AFP) levels have been measured in maternal serum and amniotic fluid in a variety of gastrointestinal abnormalities of the fetus. Maternal serum AFP levels were consistently elevated in abdominal wall defects of the fetus after 15 weeks gestation and the amniotic fluid levels were raised in 3 of the 4 patients measured. In atresia of the gastrointestinal tract and diaphragmatic hernia, serum AFP levels were usually normal unless there was an associated neural tube defect or multiple pregnancy, although the majority were not measured between 15 and 26 weeks gestation. If elevated amniotic fluid levels of AFP are used in the decision to terminate pregnancy on the assumption of a probable neural tube defect of the fetus, a proportion of terminations will be performed because of abdominal wall defects of the fetus.

ELEVATED LEVELS OF MATERNAL PLASMA ALPHA‐FETOPROTEIN AFTER AMNIOCENTESIS

An elevation of maternal AFP levels was observed in 11 of 65 cases (17 per cent) after amniocentesis. It is suggested that blood samples in which AFP levels are to be measured should always be collected before and not after amniocentesis.

Mid-trimester levels of alphafetoprotein in the screening of low birthweight.

Summary. Elevated maternal levels of alphafetoprotein (AFP) in midtrimester are believed by some to be a useful screening test for premature labour, low birthweight and low birthweight for gestation. In a prospective study on 887 randomly selected pregnant women we found that although there was an association between low birthweight and elevated AFP, the test would miss five out of every six cases of low birthweight and there would be nine false‐positives for every case correctly identified. The test is not therefore sufficiently predictive of low birthweight to be of value as a screening test for this condition.

Early amniocentesis: alphafetoprotein levels in amniotic fluid, extraembryonic coelomic fluid and maternal serum between 8 and 13 weeks

Objective— The aim was to establish a normal range of alphafetoprotein (AFP) concentrations in amniotic fluid from 8 to 12 weeks gestation, and to determine any difference between AFP levels in amniotic fluid and extraembryonic coelomic fluid.

THE SIGNIFICANCE OF RAISED MATERNAL PLASMA ALPHA‐FETOPROTEIN IN TWIN PREGNANCY

A hundred twin pregnancies were examined before 27 weeks gestation. The level of maternal plasma alpha‐fetoprotein (AFP) was correlated with outcome of the pregnancy. Forty per cent of all women had elevated plasma AFP levels. At birth the combined infant weights were greater in the women with elevated AFP; the gestational age at delivery was unrelated to the level of AFP in early pregnancy.

Absence of diurnal variation in urinary chorionic gonadotrophin excretion at 8–13 weeks gestation

It is usually recommended that a pregnancy test should be performed on the first urine specimen passed after the woman wakes in the morning. Most clinical studies involving the measurement or urinary human chorionic gonadotrophin (hCG) have used early morning specimens of urine (Banik & Givner 1979; Branch et al. 1980; Wang & Gemzell1982; Baker, Kovack & Burger 1987; Asch et al. 1988). Because various other solutes are at high concentrations in this specimen, it is assumed that hCG concentrations will also be relatively higher and, therefore, more likely to yield apositive result. However, there is no published evidence for this assumption. The aim of this study was to examine the time-totime variation of urine hCG excretion in the first trimester of pregnancy.

Short-term variation in the level of α-fetoprotein in maternal serum

Summary. Serial serum levels of α‐fetoprotein (AFP) were examined over a 24‐h period in six subjects. A short‐term variation was demonstrated which was significantly greater than that due to the assay alone, but which showed no particular pattern. These findings may explain why an‘abnormal’AFP level frequently reverts to a‘normal’level on second sampling.

Amniotic fluid levels of fibrin(ogen) degradation fragment E and alpha-fetoprotein in normal pregnancy and with fetal neural tube defect.

Amniotic fluid levels of alpha‐fetoprotein (AFP) and fibrin(ogen) degradation fragment E (FgE) were measured in 214 normal subjects and 27 pregnancies associated with an abnormal fetus (open neural tube defect or exomphalos). AFP levels showed no overlap between the normal and abnormal groups, thus confirming the reliability of the AFP assay in the detection of these abnormalities. FgE levels however showed considerable overlap and could not be used as a diagnostic parameter. Agarose gel chromatography of the amniotic fluid revealed the presence of large molecular weight FgE related antigen in open neural tube defect suggesting that leakage of proteins from exposed capillaries is responsible for the elevation of amniotic fluid protein levels.

CHANGES IN CIRCULATING ALPHAFETOPROTEIN FOLLOWING ADMINISTRATION OF MIFEPRISTONE IN FIRST TRIMESTER PREGNANCY

Summary. The occurrence of fetomaternal haemorrhage was investigated in 30 women by measuring maternal serum alphafetoprotein (AFP) levels before and after the administration of mifepristone (RU 486) for termination of first trimester pregnancy. A significant rise in AFP levels was seen in 21 women (70%), the increase ranging from 6 to 660% of baseline levels. The apparent frequency of fetomaternal haemorrhage was similar to that reported previously for surgical termination of first trimester pregnancies.