Prenatal screening for Down's Syndrome

Uptake of invasive testing following a positive triple test for Down's syndrome. Are midwives different counsellors compared with obstetricians?

A review of the uptake rate of diagnostic tests following a positive triple test was undertaken in the two maternity units of the Hull and East Yorkshire NHS Trust. In one unit, midwives were actively involved in counselling and in the other, counselling was performed by Consultant obstetricians. During the study period, there were 721 (7.1% positive rate) positive triple tests. Of these, 212 (29.4%) and 509 (70.6%) were counselled by midwives and Consultant obstetricians, respectively. There was no significant difference in uptake of amniocenteses or chorionic villous sampling with respect to the counsellor with an uptake of 60.4% in the midwife counselled group compared with 67.6% in the Consultant counselled group (p = NS). We believe the determinants of the uptake rate of a diagnostic test are patient centred if adequate counselling is provided. Midwives will continue to play a role in counselling and should be encouraged to do so to reduce the burden on obstetricians.

Participation in maternal serum screening for Down syndrome, neural tube defects, and trisomy 18 following screen-positive results in a previous pregnancy

OBJECTIVE

To determine whether women who have had a positive serum screening result for Down syndrome or neural tube defect in 1 pregnancy have a lower rate of participation in screening in their next pregnancy.

SETTING

A triple-marker screening program at a university hospital.

METHODS

Pregnancy and screening information was collected from laboratory and hospital databases to compare subsequent screening participation of women who were screen-negative and screen-positive for the risk of a fetus with Down syndrome or a neural tube defect.

RESULTS

In an age-matched comparison, 108 women who had a previous screen-positive result were significantly less likely than 108 women who were screen-negative to participate in maternal serum screening in their next pregnancy. When examined according to the type of screen-positive result, the effect was significant for both those who were screen-positive for Down syndrome and those who were screen-positive for neural tube defect. The degree of risk in screen-positive women did not significantly affect their participation in screening in the next pregnancy.

CONCLUSIONS

Anxiety related to a screen-positive result probably causes decreased participation in maternal serum screening in the next pregnancy. Reducing the screen-positive rate in prenatal serum screening would alleviate maternal anxiety and would probably lead to more stable participation.

Factors affecting women's knowledge of antenatal serum screening

Antenatal screening for fetal anomaly is offered routinely in Glasgow. This study assessed pregnant women's knowledge of the test and implications of results. Questionnaires were completed by 574 women. Knowledge of the nature and uses of the test was superior to earlier studies Two-thirds knew that screening was undertaken for Down's syndrome, and 81% for spina bifida. The majority were aware of the sample used, ages invited and gestation at which it was undertaken. Knowledge of the likely results and implications was poorer. Three-quarters were unaware that 10% of results would suggest an increased risk. Half did not realise that positive results could occur without fetal abnormality, or negative results could be falsely reassuring. Socioeconomic deprivation was associated with poorer knowledge but not lower uptake. Written information was associated with superior knowledge and higher uptake. Leaflets should be provided prior to booking, at which time resultant queries can be answered.

Towards informed decisions about prenatal testing: a review

There are now several well-documented psychological problems associated with prenatal testing programmes. These include poor understanding of tests undergone or declined, anxiety following false positive results, and false reassurance in those receiving negative test results. There is, as yet, little evidence concerning how to provide services to circumvent these. The focus of this review is upon just one of these problems: how best to inform women about prenatal testing and their reproductive options following the diagnosis of a fetal abnormality. Possible methods of improving informed decision-making either about whether to undergo testing or whether to terminate an affected pregnancy are described drawing upon research from antenatal and other health care areas. Future challenges for clinical practice and research in this area concern the range of conditions and predispositions for which prenatal testing with the option of termination should be offered.

Functional analysis of the gene encoding the clavaminate synthase 2 isoenzyme involved in clavulanic acid biosynthesis in Streptomyces clavuligerus

A Streptomyces clavuligerus mutant disrupted in cas2, encoding the clavaminate synthase (CAS2) isoenzyme, was constructed by a gene replacement procedure. The resulting cas2 mutant showed no clavulanic acid production when grown in starch-asparagine medium. However, in soy medium, the cas2 mutant did produce clavulanic acid, although in amounts less than those produced by wild-type cultures. This medium-dependent leaky phenotype correlated well with the presence of the cas1 transcript, encoding the CAS1 isoenzyme, in cultures grown in soy medium and with its absence from those grown in starch-asparagine medium. This suggested that CAS1 and CAS2 both contribute to clavulanic acid production but that their production is regulated differently. Under nutritional conditions in which cas1 expression is blocked, cas2 becomes essential for clavulanic acid production. Northern (RNA) analysis revealed that while cas1 is transcribed as a 1.4-kb monocistronic transcript only, cas2 is transcribed both as a 1.2-kb monocistronic transcript and as part of a 5.3-kb polycistronic transcript. High-resolution S1 nuclease analysis located the transcription start point of the monocistronic cas2 transcript at a C residue 103 nucleotides upstream from the cas2 start codon.