A 34-year-old healthy pregnant woman underwent serological screening at 18 weeks of gestation, the results of which indicated a low risk (risk value: 1:3900) so she and her family were awaiting a healthy baby. However, considering her advanced maternal age, the doctor advised her to adopt NIPT for a healthy fetus. After informed consent, she and her family decided to conduct NIPT at 20 weeks and 2 days of pregnancy. Surprisingly, the results showed that the fetus had a high risk of trisomy-21. The results of karyotype analysis were 47, XN, +21, suggesting that the child had trisomy-21 syndrome. After consideration, she finally chose to terminate the pregnancy to avoid the baby with trisomy-21 syndrome.