Fetal bud 0.5cm is generally about 49 days pregnant, with the length of the bud can be calculated gestational weeks, the length of the bud (cm) + 6.5 results in an integer part of the gestational weeks, gestational weeks multiplied by 7 can get the specific number of days, this method is only applicable before 12 weeks, after which you can estimate the gestational weeks by the diameter of the diameters of the biparietal and other numerical values. Some women through this formula to calculate the number of days of pregnancy and their actual days of menopause does not match, commonly found in the following two cases: 1, irregular menstruation: some women menstruation is irregular, the time of ovulation may be advanced or may be pushed back, the corresponding time of fertilization of the egg implantation will be advanced or pushed back, so there will be the number of days of pregnancy and the number of days of menopause does not match the situation. Generally speaking, women with irregular menstruation in early pregnancy can check the gestational week by the size of the fetal buds or gestational sacs; 2, poor embryonic development: the quality of some embryos is not good, resulting in slow development of the embryo, the growth of the fetal buds is slow, and the number of days of pregnancy and the number of days of menopause will not match the calculated situation. It should be noted that early pregnancy is an important period of fetal molding, easy to be stimulated by certain physical and chemical factors, and lead to miscarriage, fetal arrest, etc., so need to pay attention to the early pregnancy is recommended to supplement a small dose of folic acid, avoid coitus and strenuous exercise. If there is bleeding abdominal pain timely consultation, if you need to take medication must be consulted in advance whether it can be used. Early pregnancy due to the embryo is small, does not need too much nutrition, so you need to control weight gain, early pregnancy three months, weight gain does not exceed 2kg.