The SD value refers to the ratio of contraction and relaxation of the umbilical artery in the fetus, which is closely related to the blood supply to the fetus. If you want to understand the development of the fetus, this is important data. Generally speaking, if there are problems with the fetus, especially the placenta, this value will be abnormal. So, what is the normal range for SD values at 39 weeks?
1. Normal range. Generally speaking, if it is a normal pregnancy, as the pregnancy cycle continues to grow, the fetal value will also change, and the ratio will gradually decrease. When the fetus is almost one month old, this ratio is often less than 3. If this ratio is greater than or equal to 3, it can be considered an abnormal condition, indicating that the fetus is likely to be malnourished, and even more dangerous, it is likely to be hypoxic. These values will gradually decrease over time for pregnancies without any issues.
2. Divide into different stages. Normally, the first stage refers to the period between 26 and 28 weeks of pregnancy, during which this ratio will increase but still remain below 3; After 36 to 37 weeks of pregnancy, which is the second stage, when monitoring the umbilical artery, its blood flow impedance will be divided into three levels; In the third stage, it refers to the impedance index of the umbilical artery during delivery.
3. The situation varies at different stages. Generally speaking, if there is an abnormal situation, doctors will first consider whether it is a fetal malformation, mainly because congenital diseases of the fetus are closely related to this ratio. If you want to be diagnosed, further B-ultrasound examination is necessary.
