Prenatal screening for trisomy 18 with free beta human chorionic gonadotrophin as a marker.
OBJECTIVE
To determine the relation between maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in pregnancies complicated by trisomy 18 and establish whether prenatal biochemical screening for this condition could be developed in a way similar to that proposed for trisomy 21.


METHODS
Serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in women with singleton pregnancies affected by cytogenetically confirmed trisomy 18, uncomplicated by neural tube defect or ventral wall defect, were identified from prospective trisomy 21 screening programmes. Additionally, stored maternal serum from similar pregnancies was analysed retrospectively. Analyte concentrations from singleton unaffected pregnancies were identified from a prospective screening programme as controls. Statistical parameters of the affected and unaffected populations were compiled.


METHODS
Biochemical screening laboratories in Britain and the United States.


METHODS
52 women with singleton pregnancies complicated by trisomy 18; control population of 6661 women with unaffected singleton pregnancies.


METHODS
Median values of each analyte and their distribution in the affected and unaffected populations; detection rate of trisomy 18 and the false positive rate.


RESULTS
Maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations were significantly lower in pregnancies complicated by trisomy 18 (median values 0.71 and 0.37 respectively). By using a multivariate risk algorithm incorporating maternal age risk of trisomy 18 and the concentration of the two biochemical markers it was predicted that 50% of trisomy 18 cases (unaffected by neural tube defect or ventral wall defect) could be detected with a 1% false positive rate.


CONCLUSIONS
Second trimester biochemical screening for trisomy 18 could be a valuable addition to trisomy 21 screening programmes.
Spencer
K
K
Department of Clinical Biochemistry, Oldchurch Hospital, Romford, Essex.
Mallard
A S
AS
Coombes
E J
EJ
Macri
J N
JN
D000293:Adolescent; D000328:Adult; D015415:Biomarkers; D006063:Chorionic Gonadotropin / Q000097:blood*; D018997:Chorionic Gonadotropin, beta Subunit, Human; D002887:Chromosomes, Human, Pair 18; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D010446:Peptide Fragments / Q000097:blood*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D014314:Trisomy; D000509:alpha-Fetoproteins / Q000032:analysis*
D015415:Biomarkers; D006063:Chorionic Gonadotropin; D018997:Chorionic Gonadotropin, beta Subunit, Human; D010446:Peptide Fragments; D000509:alpha-Fetoproteins