Usually, a biparietal diameter of 81mm at 34 weeks is normal and nothing to worry about.
Biparietal diameter is the length of the widest part of the fetal head between the right and left sides. As the fetus grows, the value of the biparietal diameter changes, and you can roughly judge the development of the fetus by the size of the biparietal diameter.
A large or small biparietal diameter is abnormal and should be taken seriously.The size of the biparietal diameter of a 34-week-old fetus usually lies between 7.98cm and 9.24cm, so 81mm is generally normal.
If the biparietal diameter of the fetus is not within the normal range, you should go to the hospital in time to clarify the cause and treat it under the doctor’s guidance, so as not to affect the health of the fetus.