4D is also known as four-dimensional ultrasound, 4D ultrasound shows that the baby is four days older than the actual will not usually affect the due date. The four-dimensional ultrasound shows that the baby is four days larger than the actual, may be the menstrual cycle is shorter, ovulation time earlier, the fertilized egg implantation earlier, the fetal nutritional status is better and so on the cause, belongs to the normal phenomenon. The four-dimensional ultrasound shows that the baby is four days older than the actual general will not affect the expected date of delivery, the expected date of delivery is generally based on the last menstrual period projection, not all babies to the expected date of delivery, delayed or two weeks ahead of the time of delivery are normal phenomena. Through the four-dimensional ultrasound examination of the baby is four days older than the actual, all aspects of the development is normal, generally will not affect, if there is any discomfort in time to seek medical advice, consult the physician’s guidance.