title: Screening for trisomy 21 in twin pregnancies in the first trimester: does chorionicity impact on maternal serum free beta-hCG or PAPP-A levels?
abstract: In a study of 180 twin pregnancies I have examined the distribution of maternal serum free beta-human chorionic gonadotrophin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A), in addition to fetal nuchal translucency thickness (NT), in twins classified as monochorionic or dichorionic, based on ultrasound appearance at 10-14 weeks of gestation. In 45 monochorionic and 135 dichorionic twin pregnancies the median MoM free beta-hCG was not significantly different (1.00 vs 1.01), whilst that for PAPP-A was lower (0.89 vs 1.01) but again with no statistical significance. Previous reports of an increased fetal NT in monochorionic twins pregnancies could not be confirmed (1.03 vs 1.00). It is concluded that the existing pseudo risk twin correction algorithm is appropriate for both monochorionic and dichorionic twins in providing accurate first trimester risks for trisomy 21.
authors.affiliation: Endocrine Unit, Clinical Biochemistry Department, Harold Wood Hospital, Gubbins Lane, Romford RM3 0BE, UK. KevinSpencer1@cs.com
authors.forename: K
authors.initials: K
authors.lastname: Spencer
mesh_terms: D000328:Adult; D002823:Chorion / Q000000981:diagnostic imaging*; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004200:Diseases in Twins / Q000175:diagnosis* / Q000235:genetics; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D005820:Genetic Testing; D006801:Humans; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A