The gestational sac is 1-1.5 cm in size at 40 days of pregnancy.If the gestational sac is small in a pregnant woman, it may be due to delayed ovulation and conception, or pathogen infection. If it is large, it may be caused by early ovulation or twins, or it may be an embryonic abnormality. First, the gestational sac is small 1, physiological factors: due to emotional stress, poor diet, physical weakness, overwork and other factors, resulting in delayed menstruation before pregnancy, ovulation after the wrong time, the time of conception is late, so that the size of the gestational sac is smaller than the actual days of menopause corresponds to the small, is a normal situation. Pregnant women need to carry out a one-week dynamic examination, if the examination shows that the value of progesterone, chorionic gonadotropin are gradually rising, the gestational sac is growing normally, and gradually appearing buds and fetal heart, it can be determined that the small size of the gestational sac is due to physiological reasons, and you can continue to carry out the pregnancy, and at the same time remove the factors that are not conducive to the development of the fetal sac; 2, pathogenic infections: infection with pathogens such as mycoplasma, chlamydia, rubella virus, etc, or other toxic and harmful substances, may also lead to the pregnancy of the small size. other toxic and harmful substances, may also lead to poor development of the gestational sac. Usually this kind of gestational sac is unhealthy, and the possibility of miscarriage is higher. It is recommended to find out the cause of the problem and treat the cause, and then get pregnant again after the review is normal. Second, the gestational sac is large 1, ovulation earlier: pregnant women ovulation earlier, early fertilization time will also lead to large gestational sac. If there is a normal fetal heart and buds, the large gestational sac will have no effect on the fetus. If there is no other abnormality, there is no need to worry too much; 2, twins or multiple births: if you find two or more fetal buds, large gestational sacs may also be caused by twins or multiple births; 3, embryonic anomalies: there is a lack of tension in the empty gestational sac, but also compared to the corresponding gestational weeks of the gestational sac is larger, so large gestational sacs should be alert to the possibility of embryonic anomalies.