Early pregnancy FAQ: Picture of gestational sac size at 45 days of pregnancy In the early pregnancy, the gestational sac is a very important reference indicator because it can provide us with useful information. About 45 days into pregnancy, what is the size of the gestational sac? Below we will answer it from four aspects. The relationship between gestational sac size and embryonic development The size of the gestational sac can provide doctors with extremely important information, because the size of the gestational sac is closely related to embryonic development. Around the 45th day of pregnancy, the gestational sac is usually 0.5-1.