Hello,
The gestational sac first appears at about 4 weeks gestational age, and grows at a rate of about 1 mm a day through the 9th week of pregnancy. A
gestational sac larger than 13 mm that contains
no yolk
sac means the pregnancy is not viable, so when the sac is larger than this and there is no yolk sac, the doctor can diagnose miscarriage and a miscarriage that consists of no yolk sac would fall in the category of blighted ovum.