Under normal circumstances, the presence of a gestational sac without a yolk sac is usually indicative of pregnancy at about 5-6 weeks. If the yolk sac is not seen after 6 weeks of pregnancy, there may be an abnormality and timely improvement of relevant tests is needed. The time of pregnancy is counted from the first day of the last menstrual period and ovulation is usually around the 14th day of the menstrual cycle. It takes about 7-10 days for the fertilized egg to be formed during ovulation and then it takes about 7-10 days for the fertilized egg to be laid. Therefore, the normal appearance of a gestational sac without a yolk sac indicates that the pregnancy is within 6 weeks. If only a gestational sac is seen without a yolk sac beyond 6 weeks of pregnancy, the possibility of slow or arrested development of the embryo should be considered. If the yolk sac is not seen at 6 weeks of pregnancy but the blood HCG level is still rising, the ultrasound can be repeated in 1 week to see if the yolk sac is present.