The size of the gestational sac early in pregnancy can lend huge clues to the age of the fetus, whether the pregnancy is in the uterus or tubes and if there are any issues with implantation. A gestational sac measuring small can indicate the pregnancy is not as far along as once thought or that the pregnancy is not advancing as it is supposed to. Keep in mind that doctors usually do not perform the first ultrasound until well into the second trimester of pregnancy. When used to screen the baby, the fetus needs to be of adequate size to see the vital organs and the development of the baby. Ultrasounds in early pregnancy is usually only done if you are experiencing issues like bleeding.

Ultrasounds or sonograms don’t give a very clear image in the early stages, but in the early weeks it can give clues to why you may be bleeding or cramping. While the doctor may not be able to see the actual embryo before a certain amount of weeks, the gestational sac is usually able to be seen early in pregnancy. Read on to see why some gestational sacs may measure small in size.

Gestational Sac Measuring Small—What Does It Mean?

If you have a small gestational sac, it can mean a few things depending on your situation. Here are a few possible explanations:

Miscalculated Dates of Last Period

If your pregnancy is still in the very early stages and this is the first ultrasound, the pregnancy may be earlier than what you may have calculated by the date of your last period. It may be that you ovulated later in your cycle. Most cycles are 28 days with ovulation around day 14 of the cycle. Some women have longer cycles and ovulate later, which means the pregnancy may not be as advanced.

Your doctor may choose to follow you closely over the next few weeks to see if the sac and fetus are growing as they should and then give you a new due date based on ultrasound measurements.

The Pregnancy Is Not Advancing

While this is rare, it may be the first sign that the pregnancy is not advancing as it should. It doesn’t always mean you are going to have a miscarriage, but the doctor will continue to monitor your ultrasounds often to see if your pregnancy will continue.

There is an issue with “low progesterone levels” early in pregnancy and if the gestational sac measures small, the doctor can test for progesterone levels and treat it with replacement.

According to studies done by the National Institute of Health or NIH, “small gestational sac occurs in 1.9% of pregnancies and only 80% of those end in miscarriage.” What this means is that some pregnancies do go on to full term after the gestational sac measures small and there is hope.

Gestational Sac Measuring Small—Should You Worry?

Not always. While there is a cause for concern if a gestational sac measures small, if the pregnancy is still very early then you may have an issue with the actual age of the pregnancy. If the pregnancy is beyond 8 to 10 weeks then there are concerns that the pregnancy is not viable.

At around the 6th week of pregnancy, there should be a visible “pole” in the sac and corresponding heartbeat. If this is not present, then a fetus may have never developed in the sac at all and it is in fact a “pseudo-sac” or “pseudo-pregnancy.”

In either case, the doctor will most likely draw blood levels for the pregnancy hormone, hCG (Human Gonadotropic Hormone) to monitor and see if they are going up or down. If there is no visible pole and the hCG continues to rise, the doctor may opt to “watch and wait” to see if a pole develops.

Other Moms' Experiences

Alisa, 24 Weeks Pregnant

“I want to share my story to possibly bring you some peace of mind. I had my first ultrasound when I was 8 weeks pregnancy. The technician said my gestational sac only measured 7 weeks and was really small. The tech said there was a possibility of miscarriage. I found an online Doppler rental service and listened to my baby’s heartbeat every day until I was 13 weeks pregnancy and it was fine! At my sonogram at 14 weeks, the sac had caught up and measured the perfect size. I am in my 24th week of pregnancy and things are still measuring just fine and my baby is fine. The tech said that the gestational sac needs to be at least 5mm bigger than the baby’s crown to rump length and my sac was 7mm larger. It is only when the sac is 5mm or smaller that the miscarriage risk is 80%. I feel very blessed that everything turned out okay.”

Cindy, 6 Weeks Pregnant

My pregnancy was confirmed 4 days ago but my doctor calculated me to be between 6 and 7 weeks pregnant. She sent me for an ultrasound and there was a very small sac measuring at about the 4th week of pregnancy. However, the embryo inside was measuring 6 weeks and there was a heartbeat. The doctor was very concerned and told me we needed to monitor the sac “closely” to make sure it catches up with the size of my baby. She also told me that the chance of miscarriage in this situation is 80%. I didn’t have any problems with my first pregnancy and don’t know why the gestational sac is so small.

3 weeks later I suffered a miscarriage. The sac never caught up to my growing baby and the baby passed away. I had to have a DNC because they could no longer find a heartbeat and my body would not miscarry on its own. I am recovering and feel good physically. I also feel lucky to have my daughter and for now will try to focus on the positive.

Gina, 8 Weeks Pregnant

The last few weeks I have had some light spotting and just last Friday I was bleeding like a period. My partner took me to the Emergency room where they drew an hCG level and they were over 5,000. They said I was around 7 weeks and 5 days. My hCG levels were up from 1,100 the Friday before. They did an ultrasound and there was a gestational sac, but they could not see a baby or heartbeat in the sac. It was measuring at 5 weeks and 4 days, but by my dates I should be 8 weeks pregnant. They drew my blood again after the ultrasound and the hCG went up to over 6,000. I go back for another ultrasound in a few days. They say it may just be that I ovulated later in my cycle and the pregnancy is still very early. I have all of the symptoms of pregnancy and I can just feel there is a baby growing inside of me.