Fetal development is four weeks smaller than the expected date of birth or need to be vigilant, may be normal, there may be growth and developmental defects caused. The due date is an estimated date, it may be advanced or pushed back 1-2 weeks is also the normal range, so the fetus currently has a small development, it may be ovulation irregularity also has a certain relationship, usually there is no abnormality in the obstetric examination, then it is recommended that you can be regularly observed, on the supplemental nutrition. If the placental dysfunction or external environmental factors, then it is easy to lead to fetal development is limited, then this time you need to consult a doctor in a timely manner, choose symptomatic treatment methods. Therefore, if the fetus is 4 weeks small, it is necessary for the doctor to evaluate the fetus in conjunction with the woman’s menstrual history and other developmental indicators, and if necessary, perform an amniocentesis to determine whether it is a pathological condition and whether intervention is needed.