The increased ratio of pulmonary artery to aorta at 27 weeks may be caused by incomplete maturation, congenital cardiovascular disease, etc. It needs to be treated by reviewing the 4D ultrasound, good pregnancy health care and surgery. The increase in the ratio of the pulmonary artery to the aorta at 27 weeks may be due to the incomplete maturation of the fetal cardiovascular system. If the ratio is not obvious, the pregnant woman needs to have another 4D ultrasound after 2~4 weeks to determine whether there is still an abnormality. If the ratio is no longer increasing, it is only caused by incomplete maturity, and the pregnant woman should pay attention to the obstetric examination on time and do a good job of pregnancy care. However, if the ratio is larger, it is likely to be caused by congenital cardiovascular disease, etc., which needs to be evaluated by specialists and, if necessary, treated with surgery after delivery. Pregnant women are advised to consult a doctor as soon as they notice an increase in the ratio of the pulmonary artery to the aorta at 27 weeks of gestation, to complete the relevant examinations and to standardize the treatment.