Trisomy 18: Prenatal Diagnosis and Outcome in a Tertiary Care Fetal Medicine Center in South India

Abstract

Edwards' syndrome (trisomy 18) is the second most common aneuploidy known in humans, with an overall incidence of 1 in 6,000 live births. It occurs due to the presence of complete or part of an extra copy of chromosome 18 in all or a few body cells of the affected fetus, and it causes major anomalies in the organ systems. Despite this, an accurate diagnosis is often not made antenatally due to its very varied phenotype and the subtle nature of some of the common and consistent findings associated with this condition. This leads to lapses or delays in cytogenetic confirmation as well as delays in decision regarding termination of pregnancies with this mostly lethal fetal aneuploidy. We describe the prenatal profile of 45 confirmed cases of trisomy 18 at a tertiary fetal medicine unit. The presence of a combination of ultrasound (US) findings described in these cases will help alert sonologists and clinicians to suspect this condition and offer a confirmative cytogenetic test without delay for prenatal diagnosis. This study describes the prenatal diagnostic profile of cytogenetically confirmed trisomy 18 cases in a tertiary fetal medicine center in India. A retrospective analysis of records of 45 prenatally diagnosed trisomy 18 cases at a single tertiary fetal medicine center over a period of 11 years was done. Data were collected to describe maternal demography, indication for evaluation, major and minor US findings (trimester-wise), type of invasive test, and gestational age at diagnosis. Outcomes in terms of pregnancy termination, miscarriage, stillbirth, or livebirth were documented. Presenting at a mean maternal age and gestation age of 31.7 years and 22 + 5 weeks, respectively, 41/45 (91%) fetuses showed major and 40/45 (89%) showed minor US findings with an overall US sensitivity of 100%. The most common major US finding was a cardiac anomaly in 26 (57.8%) patients, while clenched fist with pointing index finger, observed in 17 (37.8%) cases, was the most common minor US finding. Fetal growth restriction (FGR) was noted in 20 (44.4%) patients. After cytogenetic confirmation, 37.8% underwent termination, 17.8% had a fetal demise, and only 11.1% had live birth with the longest survival noted at 5.5 months postnatally. Gender was documented in 13 fetuses with a male-to-female ratio of 0.6. A meticulously performed US examination can detect a combination of anomalies that could alert the sonologist to the possibility of trisomy 18. While the US profile could vary among fetuses, an understanding of the spectrum of the anomalies commonly seen in these fetuses would enable caregivers to reach an early accurate diagnosis, and offer appropriate genetic counseling and pregnancy decisions in these cases.