Mid-trimester Down syndrome screening results within normal range

Mid-trimester screening—also referred to as second-trimester screening—is a preliminary assessment conducted during the mid-pregnancy period to estimate the risk of the fetus developing congenital or genetic disorders. So, what constitutes a normal result for mid-trimester Down syndrome screening?

Normal Range for Mid-Trimester Down Syndrome Screening

The normal cutoff value for mid-trimester Down syndrome screening is 1:308. Minor deviations from this value are common and should not cause undue concern for pregnant women. Down syndrome screening is primarily performed between gestational weeks 16 and 20, and assesses the risk of trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and open neural tube defects. Prior to undergoing screening, a recent ultrasound report is required to confirm gestational age and fetal viability. If medically appropriate, blood sampling may be performed in the morning after an overnight fast.

Women aged over 35 years and those carrying twins are generally not recommended to undergo Down syndrome screening. Advanced maternal age is an indication for direct diagnostic testing via amniocentesis. In cases where Down syndrome screening indicates high or borderline risk, consultation with a genetic counseling clinic at a higher-level medical institution is advised; amniocentesis may be warranted based on clinical judgment.

The purpose of Down syndrome screening is to assess the likelihood of fetal Down syndrome. This screening is typically performed between gestational weeks 15 and 20+6 days. A venous blood sample is drawn from the pregnant woman to measure serum levels of human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and alpha-fetoprotein (AFP); these values are then used to calculate the individualized risk for Down syndrome. Infants with Down syndrome commonly exhibit intellectual disability, characteristic facial features, multiple organ malformations, and reduced functional independence; currently, no definitive cure exists in clinical practice. We hope this information has been helpful. Wishing you good health and happiness!