The Development of Action Lines in an Australian Maternal Serum Alphafetoprotein Screening Service for Neural Tube Defects

EDITORIAL COMMENT: In this careful study, 6 of 7 mothers carrying fetuses with neural tube defects were found to have raised serum alphafetoprotein levels (more than 2.5 multiples of the median) in the second trimester, out of 3,182 pregnancies tested. In the other 65 patients with elevated AFP levels there were 4 fetuses with major malformations and many with other important clinical complications. All of these fetal malformations were identifiable by ultrasonography. This paper does not consider the association between low AFP levels and Down syndrome, although this is another reason why screening maternal serum AFP levels could be advocated, since it can offer a detection rate of 28% by selecting less than 3% of unaffected pregnancies for amniocentesis, a better yield than using maternal age alone (Cuckle HS, Wald NJ, Thompson SG. Estimating a woman's risk of having a pregnancy associated with Down's syndrome using her age and serum alphafetoprotein level. Br J Obstet Gynaecol 1987; 94: 387 ‐ 402 — this review concluded that screening for Down syndrome using both maternal age and serum AFP is more efficient than using age alone and that, where antenatal serum AFP screening programmes are in progress, there is no justification for not using both). The authors leave it to the reader to ponder whether or not maternal serum AFP screening should be offered to all patients. At present it is not performed routinely in any of the teaching hospitals in Melbourne. Should it be? If so, must the patient be counselled regarding the reasons for screening before being offered the test? Is the test less important now that ultrasonography performed at 16 ‐ 18 weeks' gestation can identify all neural tube defects and many other major malformations — but not Down syndrome, regardless of the fact that several ultra‐sonographic stigmata of Down syndrome have been reported. At present ultrasonography is performed in 60 ‐ 80% of pregnancies and a structured referral screening programme for fetal malformations is being introduced in some hospitals. Nonetheless the benefits of routine ultrasonography remain in order of merit: (i) determination of gestational age (ii) diagnosis of multiple pregnancy (iii) siting of the placenta and (iv) recognition of fetal anomalies. It is estimated that routine screening will detect a major fetal malformation in 0.3% of low risk pregnancies i.e. approximately 90% of fetuses with major malformations will escape identification by such a programme. A recent issue of this journal (1987; 27:92) enumerated the antenatal investigations currently judged to be ‘essential’ or ‘recommended’. The case for inclusion of hepatitis B antigen and group B beta haemolytic streptococcus testing has been reemphasized (Cruz AC, Frentzen BH, Belinke M. Hepatitis B: A case for prenatal screening of all patients. Am J Obstet Gynecol 1987; 156: 1180–1183; Morales WJ, him DV, Walsh AF. Prevention of neonatal group B streptococcal sepsis by the use of a rapid screening test and selective intrapartum chemoprophylaxis. Am J Obstet Gynecol 1986; 155:980–983). Should maternal serum alphafetoprotein screening be added to the list of antenatal tests? Summary: A retrospective study covering the period from January 1, 1980 up to June 30, 1982 was conducted, producing the first definitive normal range for maternal serum alphafetoprotein from the Royal North Shore Hospital in Sydney. The normal range established is based on and applicable to the pregnant women tested at this NSW laboratory. Maternal serum alphafetoprotein levels had been determined by radioimmu‐noassay for 3,182 pregnancies between 13 and 20 weeks' gestation. Five anence‐phalics and 2 open spina bifidas were noted in the study. Only one of these abnormalities (spina bifida) was associated with maternal serum alphafetoprotein levels within the normal range, the remainder all having elevated levels. Low false positive and false negative rates of 1.16% and 0.03% respectively were obtained in this study.