Early Pregnancy Scan
If you have just found out you are pregnant — congratulations. This article covers what to expect from your first pregnancy ultrasound: when it should be done, how it is performed, and what your doctor will be looking for. If you are still at the stage of confirming your pregnancy with a home test or blood test, you may find our Pregnancy Confirmation article helpful to read first.
When Should the First Pregnancy Ultrasound Be Done?
The earliest an ultrasound can detect a pregnancy is around 4.5 to 5 weeks of gestation — but seeing very little at this stage is entirely normal and can cause unnecessary worry. In most cases, 6 to 7 weeks is the recommended time for a first scan. By this point, the gestational sac, yolk sac, and early fetal pole are usually visible, and fetal cardiac activity can often be detected. This makes the scan far more informative and reassuring.
If you have just missed your period and are keen to confirm the pregnancy sooner, a urine or blood pregnancy test is a good first step. An ultrasound can then follow once the pregnancy is far enough along to be seen clearly. More detail on that process is covered in our Pregnancy Confirmation article.
How Is the Scan Performed?
In early pregnancy, ultrasound is most commonly performed transvaginally (TVS — transvaginal sonography). This approach provides much clearer images than scanning over the abdomen at this stage, because the uterus is still small and low in the pelvis and the embryo is very small.
Your doctor may first attempt a transabdominal scan over your abdomen. If the pregnancy is clearly visible and measurements can be obtained, that may be sufficient. However, if the view is limited or the gestational age is very early, a transvaginal scan will be recommended.
For a transvaginal scan, you will be asked to change and lie comfortably on the examination table. A slim, covered probe is gently inserted into the vagina. The procedure is performed with full privacy and respect. While some women find it slightly uncomfortable, it should not be painful. The scan usually takes around 10 to 15 minutes.
What Does the Doctor Look for?
1. Is the pregnancy inside the uterus?
The first and most important question is whether the pregnancy is intrauterine — located inside the uterus as expected — or outside of it. A pregnancy located outside the uterus is called an ectopic pregnancy and is most commonly found in the fallopian tube. This is a serious condition that requires prompt treatment.
2. What pregnancy structures can be seen?
Pregnancy findings appear in a predictable sequence as gestation advances:
– Around 4–4.5 weeks: A gestational sac becomes visible inside the uterus — the first sign of an intrauterine pregnancy.
– Around 5–5.5 weeks: The yolk sac appears as a small ring within the gestational sac.
– Around 5.5–6 weeks: The fetal pole (early embryo) becomes visible alongside the yolk sac.
3. Is there a fetal heartbeat?
Fetal cardiac activity can be detected when the embryo measures as small as 2 mm. Once the embryo reaches 7 mm, cardiac activity should be visible in a normally developing pregnancy. The heart rate in early pregnancy is typically around 90–110 beats per minute at 6 weeks, rising to 140–170 bpm by 9–10 weeks.
4. How many pregnancies are there?
The number of gestational sacs and embryos is carefully assessed to determine whether you are carrying a single pregnancy, twins, or more.
5. How far along is the pregnancy?
Once a fetal pole is visible, the doctor measures the crown-rump length (CRL) — from the top of the head to the bottom — to accurately estimate gestational age. In the first trimester, CRL dating is the most reliable method and will be calculated against your last menstrual period (LMP). From this first scan a due date will be provided. For more on how gestational age and your due date are calculated, see our Due Date Calculation article.
6. Are the ovaries and surrounding structures normal?
The ovaries and adnexa (the tissue and structures surrounding the uterus) are also examined. This helps identify ovarian cysts, the corpus luteum (a normal finding in early pregnancy), or any other findings that may need follow-up.
What If It Is Too Early to See Much?
If the scan is performed very early and the findings are inconclusive — for example, a gestational sac is seen but no embryo or heartbeat yet — your doctor will typically recommend a follow-up scan in 1 to 2 weeks. This is a common and expected part of early pregnancy monitoring and does not necessarily mean anything is wrong. However, if you have symptoms that might indicate an abnormal pregnancy, such as bleeding or pelvic pain, coupled with an inconclusive ultrasound, your doctor might recommend a blood test to check your BhCG levels, and close monitoring to rule out abnormal pregnancy such as an ectopic pregnancy.
When Should You Seek Immediate Attention?
If you experience vaginal bleeding, pelvic pain, or shoulder tip pain at any point in early pregnancy, please do not wait for your next scheduled appointment. See your doctor or go to an emergency department promptly. These symptoms require urgent evaluation to rule out an ectopic pregnancy or miscarriage, both of which can have serious consequences if not identified quickly.
Is an Early Pregnancy Ultrasound Safe?
Yes. Diagnostic ultrasound is considered safe in pregnancy, including in the first trimester. Extensive research has found no causal relationship between ultrasound exposure and adverse pregnancy outcomes. As with all medical imaging, it is performed following the ALARA principle (As Low As Reasonably Achievable), meaning that exposure is kept to the minimum needed to obtain the necessary information.
References
1. Doubilet PM, Benson CB, Bourne T, et al.; Society of Radiologists in Ultrasound Multispecialty Panel on Early First Trimester Diagnosis of Miscarriage and Exclusion of a Viable Intrauterine Pregnancy. Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med. 2013;369(15):1443-1451. doi:10.1056/NEJMra1302417.
2. American College of Obstetricians and Gynecologists. Ectopic Pregnancy: ACOG Practice Bulletin No. 193. Obstet Gynecol. 2018;131(3):e91-e103. (Reaffirmed 2022).
3. Cunningham FG, Leveno KJ, Dashe JS, Hoffman BL, Spong CY, Casey BM. Williams Obstetrics. 26th ed. New York: McGraw-Hill; 2022.
4. International Society of Ultrasound in Obstetrics and Gynecology. ISUOG Practice Guidelines (updated): performance of first-trimester ultrasound scan. Ultrasound Obstet Gynecol. 2023;61(1):127-143. doi:10.1002/uog.26106.
Maternal–Fetal Medicine Specialist in Bangkok
Dr. Narisra Srikureja Firer (Dr. Niti)
Dr. Niti is a Bangkok-based OBGYN with subspecialty training in Maternal–Fetal Medicine (MFM). She provides comprehensive care for women across all stages of life, including pregnancy care, deliveries, and general gynecological conditions.
She dedicates her time to private practice at Ruamjairak Hospital and Mission Hospital, and serves as a Maternal–Fetal Medicine Consultant at a large government tertiary care center.
To read Dr. Niti’s full bio, click here.
