Impact of Maternal Body Mass Index (BMI) on the Performance of Non-Invasive Prenatal Testing (NIPT)

Noninvasive prenatal testing (NIPT) is widely used to screen for common fetal trisomies. Fetal fraction (FF), essential for NIPT accuracy, can be influenced by maternal obesity. This study analyzes NIPT results by obesity status and suggests strategies to improve performance.

This observational retrospective study evaluated FF, gestational age, number of re-works and re-sampling, and frequency of non-meaningful and aberrant results in different BMI categories in 26,000 pregnancies that underwent NIPT from April 2023 to March 2024.

BMI was significantly associated with higher re-working and re-sampling needs due to non-meaningful results. Low FF (< 4%) occurred in 4.5% of women with normal weight (NW) and in 19.5% of obese women (BMI > 30), with the highest prevalence of 35.5% in women with severe obesity (BMI ≥ 40). The effectiveness of re-working was 56% in obese women (BMI > 30) compared to 79% in a normal weight category (NW). The overall observed positivity rate in obese women was 0.45%, significantly lower than that in NW (0.94%).

Our results indicate that NIPT performs suboptimal in obese women due to too low FF. This should be addressed during pre-test counseling and strategies such as re-sampling instead of re-working, or postponing NIPT until after 12 weeks of gestation may be advisable.