40 weeks of fetal labor does not start may be the date of estimation error, cephalic disk disproportion, estrogen-progestin hormone ratio imbalance and other reasons. 1. Wrong date estimation: Since the expected date of delivery is estimated based on the date of menstruation, the estimated date is not completely accurate, 40 weeks of labor may not start is also a normal phenomenon, if the normal pregnancy checkups do not have to be special treatment. 2. Cephalic disproportion: the size and location of the fetal prenatal area is not commensurate with the size and shape of the pelvis, there is no way for the fetus to enter the pelvis normally, 40 weeks of pregnancy, the start of the fetus will also be delayed. 3. estrogen-progestin ratio imbalance: 40 weeks pregnant body estrogen-progestin ratio imbalance, such as estrogen levels decrease, progesterone levels increase, progesterone inhibit uterine contractions, will also make the fetus delayed start. 40 weeks pregnant fetus is not launched first observation, under the guidance of the doctor for diagnosis and treatment.