Early Pregnancy Ultrasound Results

Researchers have mapped out the expected measurements for specific points in early pregnancy, An early ultrasound scan can give a doctor important information about gestational age and viability.

An ultrasound is a highly accurate means of dating a pregnancy. In a normal pregnancy, ultrasound can provide an estimate of the gestational age to within five to seven days of accuracy. When a woman is having miscarriage symptoms, a doctor may order one or more ultrasounds to determine whether the pregnancy is viable.

How Early Pregnancy Ultrasound Works

In the first trimester, doctors usually use a transvaginal rather than abdominal ultrasound. The transvaginal ultrasound provides the most accurate information, given that the early developing gestational sac and fetal pole are extremely tiny at this point. A transvaginal ultrasound can get closer to the developing pregnancy.

In a transvaginal ultrasound, the doctor or technician inserts a thin probe into the vagina. During the ultrasound, they take a series of measurements, including the size of the gestational sac, the size of the yolk sac, the length of the fetal pole, and the heart rate.

In an abdominal ultrasound, the woman will be asked to come to the scan with a full bladder, because this positions the uterus in a way that makes it easier to obtain measurements. The doctor or technician then spreads a gel over the lower abdomen and uses a transceiver to take measurements from a number of angles.

Expected Ultrasound Results by Week in Early Pregnancy

Gestational Age Milestone Visible on Ultrasound
4 weeks Possible endometrial thickening, or no evidence of pregnancy
5 weeks Gestational sac
5.5 to 6 weeks Yolk sac
5.5 to 6.5 weeks Fetal pole; possible fetal heartbeat
6.5 to 7 weeks Fetal heartbeat

These are averages for when specific early pregnancy developmental points become detectable by transvaginal ultrasound. Generally, abdominal ultrasound is less sensitive and may not detect these milestones until a week or later in the pregnancy.

Remember that any uncertainty about the date of ovulation could affect what the ultrasound will show at any point in early pregnancy.

Early Ultrasound for Determining Miscarriage

Female nurse performing ultrasound on pregnant woman in examination room
Hero Images / Getty Images

The results of an ultrasound are compared to what is expected for the gestational age of a pregnancy. The gestational age is calculated by the number of weeks since the last menstrual period; however, this method generally assumes a 28-day cycle with ovulation occurring on the 14th day. Many women have shorter or longer cycles and do not ovulate on the 14th day, and this could affect what an ultrasound should show in the development of the pregnancy.

For example, if a woman has a 35-day menstrual cycle, she most likely ovulates around the 21st day of her menstrual cycle (because ovulation usually occurs two weeks before the menstrual period would begin). If the woman became pregnant and had an ultrasound scan six weeks from her last menstrual period date, her normally developing pregnancy would measure with a gestational age of five weeks.

If the woman did not know that she ovulated on the 21st day of her cycle, she might worry unnecessarily that she was having a miscarriage. Her early ultrasound would show only five weeks of development in her pregnancy when she was technically six weeks pregnant.

Similarly, not everyone meticulously tracks the start of the menstrual period. If a woman cannot remember when her menstrual period started and guesses the wrong day, even if she does have a typical 28-day cycle, this could also change the expected results of an ultrasound scan.

In early pregnancy, the gestational sac and embryo change drastically every day, so being off even by a few days with dating can make a difference in whether or not the ultrasound should detect a heartbeat or reach certain measurements.

When Results Are Uncertain

Pregnant couple having sonogram
John Fedele / Getty Images

Sometimes an ultrasound will give uncertain results. For example, if a woman is seven weeks pregnant and the ultrasound does not reveal a fetal heartbeat, the doctor may order another ultrasound in a week. The pregnancy could still be normal but simply off by a few days in the dating. Or, the dating could be accurate, but still within the margin of error for when the heartbeat becomes detectable.

Similarly, if an ultrasound reveals an empty gestational sac, this could still be a normal finding if the pregnancy is early along. The developing baby is too small to be seen on ultrasound until about five weeks of gestation. In this case, the doctor may opt to repeat the ultrasound at a later date.

In either of these cases, the ultrasound results may indicate a miscarriage or the pregnancy may still be normal. If the subsequent ultrasound shows that the pregnancy has continued developing, the earlier results can be attributed to problems with dating.

If the subsequent ultrasound still shows abnormal development, the doctor can conclusively diagnose a miscarriage. In many cases, the doctor cannot make a diagnosis based only on one early pregnancy ultrasound scan. The wait for the repeated ultrasound can be emotionally very difficult, but it may be necessary to avoid a misdiagnosis.

Other Diagnostic Information

Midwife taking blood sample from arm of pregnant woman
ADAM GAULT/SPL / Getty Images

If there is any question as to whether or not a woman is having a miscarriage based on an ultrasound scan, the usual course of action is to do another ultrasound in a few days or a week. Sometimes, however, the presence of other diagnostic information can help a doctor to interpret ultrasound results.

For example, if a woman has a positive pregnancy test the day of her missed period, followed by confirmation with hCG blood test results, and an ultrasound four weeks later shows a pregnancy at only five weeks gestational age, the doctor may conclude that the woman has had a missed miscarriage. The positive pregnancy test a month earlier would indicate that the pregnancy should be more developed.

In addition, if the ultrasound measurements indicate an embryo and/or heartbeat should be present and it is not, the doctor may diagnose miscarriage. The American College of Obstetricians and Gynecologists guideline is that if the crown-rump length is 7 mm or greater with no heartbeat, or if the mean sac diameter is 25 mm or greater and there is no heartbeat, pregnancy failure has occurred.

Ultrasounds in Late Pregnancy Loss

Medical consultation
VOISIN/PHANIE / Getty Images

As pregnancy progresses, ultrasound becomes more and more accurate for determining the viability of a pregnancy. If an ultrasound in the second or third trimester shows that a baby has no heartbeat, this is considered conclusive for diagnosing a missed miscarriage or impending stillbirth.

Was this page helpful?
Article Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Skupski DW, Owen J, Kim S, et al. Estimating gestational age from ultrasound fetal biometrics. Obstet Gynecol. 2017;130(2):433-441. doi:10.1097/AOG.0000000000002137

  2. Kaur A, Kaur A. Transvaginal ultrasonography in first trimester of pregnancy and its comparison with transabdominal ultrasonography. J Pharm Bioallied Sci. 2011;3(3):329-38. doi:10.4103/0975-7406.84432

  3. Bickhaus J, Perry E, Schust DJ. Re-examining sonographic cut-off values for diagnosing early pregnancy loss. Gynecol Obstet (Sunnyvale). 2013;3(1):141. doi:10.4172/2161-0932.1000141

  4. ACOG practice bulletin no. 200: Early pregnancy loss. Obstet Gynecol. 2018;132(5):e197-e207. doi:10.1097/AOG.0000000000002899

Additional Reading