First Trimester Combined Aneuploidy Screening for Trisomy 21: A Three Years Retrospective Study

Introduction: Prenatal testing also known as maternal screening is primarily performed to screen out most common chromosomal anomalies in the foetus using maternal blood. It provides an accurate and sensitive assessment of a patient’s risk of carrying a foetus with chromosomal anomalies.

Aim: To study the first trimester prenatal screening using a Foetal Medicine Foundation (FMF) certified platform to estimate the risk of foetal trisomy 21.

Materials and Methods: This retrospective study was conducted at Global Reference Laboratory, Mumbai, Maharashtra, India, from January 2018 to March 2021 on samples of 86118 pregnant Asian women with respect to age, the risk cut-off was set at 1:250 for trisomy 21. The study included determination of free β-human Chorionic Gonadotropin (β-hCG) and Pregnancy Associated Plasma Protein-A (PAPP-A) in maternal serum, ultrasound studies of Crown Rump Length (CRL), Nuchal Translucency (NT) and nasal bone and maternal characteristics. Concentration of biochemical parameters was expressed in Multiple of Medians (MoM) respective to gestation age. Risk assessment of trisomy 21 was analysed using lifecycle software cut-off being 1:250 at sampling.

Results: The overall positive risk (high risk) for trisomy 21 obtained was 2.58%, association with advanced maternal age, history of Insulin dependent diabetes mellitus and absent nasal bone status. Biochemically, the MOM of β-hCG was high with mean MoM of 2.40 (>1.5) and MoM of PAPP-A was low with mean MoM of 0.64 (≤0.6).

Conclusion: This study enabled us to understand the importance of prenatal testing, a non invasive screening of chromosomal disorders like trisomy 21 which gives the advantages of early counseling and diagnosis quite as early as in the first trimester of pregnancy. It helps in drastically reducing the use of invasive procedures associated with risk of miscarriages. It is suggested that screening for chromosomal abnormalities be offered in all antenatal women irrespective of age and parity.