The causes of irregular gestational sacs include wrong calculation of the time of conception, problems with the embryo, and maternal infection. 1. Incorrect calculation of the time of conception: If a woman’s menstruation is delayed, it will cause ovulation to be delayed backward, and the time of conception will become late. If the calculation is made according to the first day of the last menstruation, the calculation of the time of conception may be incorrect, and therefore the gestational sac will feel small. 2. Problems with the embryo: Irregularity of the gestational sac may also be caused by problems in the development of the embryo itself or poor quality of the embryo. 3. Maternal infection: If the mother is infected with pathogens such as chlamydia, mycoplasma or viruses during pregnancy, which affects the development of the embryo, the pregnancy sac may also be irregular. When a pregnant woman has an irregular or small gestational sac, it is recommended that she go to the hospital in time to clarify the cause of the problem and then carry out targeted treatment.