Trisomies due to maternal chromosome non-disjunctions usually occur within 3rd and 4th decades of life with an increasing ratio. Fetal chromosomal anomalies can be detected by diagnostic and screening tests used depending on the gestational age. In this report, fetal chromosome analysis was performed in a pregnant individual with a high (1/90) risk of trisomy 18 in serum screening test and the karyotype was found to be 47,XY,t(2;18)(p21;q23),+18 in the fetus. Parental analysis were performed and unbalanced fetal karyotype was found to be resulted from balanced maternal 46,XX,t(2;18)(p21;q23) translocation. Prenatal level II USG performed at the 21st week of gestation revealed intrauterine growth retardation, typical clenched-hand posture and single umbilical artery in the fetus. The family decided termination of pregnancy after genetic counselling. Unbalanced karyotypes can be seen in families having balanced translocations. But this kind of unbalanced karyotypes due to 3:1 missegragation is rarely seen. In this report, a rare trisomy 18 case having 47,XY,t(2;18)(p21;q23),+18 karyotype due to 3:1 meiotic missegragation has been reported.
Keywords: Meiotic missegregation, 3:1 missegragation, trisomy 18, prenatal diagnosis
