Patient: description of condition (onset time, main symptoms, hospital visit, etc.): (1) My last period was December 31-January 3, and my periods are usually on time. (2) I had my Down’s test on April 26th. (3) On the report, the doctor miscalculated my gestational week and wrote that I was 18 weeks and 1 day pregnant. (4) The trisomy 18 index is 1:287. (5) My DOB is 1985-9-27 and my weight is 52kg. 1) Recalculate my gestational week. 2) Is the trisomy 18 still on the high side? 3. Do I need further examination? Doctor：Hello, at present, all hospitals use the gestational week for Down’s syndrome screening not according to the last menstrual period, but according to the biparietal diameter of the fetus, and the statistical conclusion of the relevant software is also based on the biparietal diameter, so the gestational week is correct. However, the reference value of the Down’s syndrome report varies from hospital to hospital, so it is recommended to take the next step according to the doctor’s recommendation in the receiving hospital, such as amniocentesis if necessary, and wish you a good pregnancy!