When the buds are 2.5cm, it is usually around 9 weeks of pregnancy. In early pregnancy, the number of weeks can be estimated from the last menstrual period, but for women who usually have irregular periods, there may be a large error, so it is more accurate to measure the size of the fetal buds by ultrasound. Usually, you can use the formula of fetal bud (cm) + 6.5 as the number of weeks of pregnancy to make an approximate estimate, and the calculation can be obtained when the fetal bud is 2.5cm at about 9 weeks of pregnancy. Since the degree of embryonic development is related to parental genetics and personal circumstances, there may still be some error in the calculation, and the gestational age can be estimated by measuring the head and hip length of the fetus after the 11th week of pregnancy, which is a more accurate result. At 9 weeks of pregnancy, the fetus already has a human shape, and the placenta is gradually forming, you can go to the hospital to prepare for the birth examination, and regularly through the ultrasound test results and blood hCG and progesterone levels, a comprehensive evaluation of the embryonic development. In early pregnancy, we should pay attention to a balanced diet, rationally strengthen the nutrition, under the guidance of the doctor to supplement folic acid, pay attention to the regularity of work and rest in life, do not stay up late, avoid strenuous activities or heavy physical labor.