A biparietal diameter of 81mm at 34 weeks of pregnancy is usually normal and nothing to worry about. Biparietal diameter is a reference indicator used to determine whether the development of the fetus is normal during a woman’s pregnancy, and the normal value of the biparietal diameter during a woman’s 34-week pregnancy ranges from 7.98cm to 9.24cm, and the biparietal diameter of 81mm is 8.1cm, which is within the range of this interval. Therefore, it is usually normal in the absence of other symptoms in the organism. It is recommended that women maintain balanced nutrition during pregnancy, avoiding the intake of oily foods that may lead to a large biparietal diameter, and maintaining normal data indicators. Women are advised to pay more attention to the changes in their bodies during pregnancy and to undergo regular pregnancy checkups to detect problems and intervene in a timely manner, so as to avoid delays and other effects.