A transvaginal ultrasound produces detailed images of the uterus, ovaries, fallopian tubes, and cervix. Because the probe sits just centimeters from these structures, it picks up far more detail than an abdominal scan, making it the preferred tool for evaluating early pregnancy, unexplained bleeding, pelvic pain, fertility, and suspected growths like cysts or fibroids.
Early Pregnancy Milestones
One of the most common reasons for a transvaginal ultrasound is confirming and dating an early pregnancy. A transabdominal scan often can’t see much before 7 or 8 weeks, but a transvaginal approach reveals pregnancy structures significantly earlier.
At 4 to 5 weeks, the gestational sac becomes visible inside the uterus. By 5 to 6 weeks, a yolk sac appears within that gestational sac, which is the first definitive proof that the pregnancy is located inside the uterus rather than in a fallopian tube. Around 6 to 7 weeks, the fetal pole develops and a heartbeat can be seen on screen. These milestones help your provider confirm viability, estimate a due date, and rule out ectopic pregnancy or early miscarriage.
Ectopic Pregnancy
When someone has a positive pregnancy test but experiences sharp pelvic pain or abnormal bleeding, a transvaginal ultrasound is the primary tool for checking whether the pregnancy has implanted outside the uterus. The most definitive sign is seeing a yolk sac or embryo in the tissue beside the uterus rather than inside it. If an embryo with cardiac activity is visible outside the uterus, that confirms an ectopic pregnancy and typically means urgent surgical referral.
Sometimes the scan shows neither an intrauterine nor an ectopic pregnancy. This is called a pregnancy of unknown location, and it usually means the pregnancy is too early to see. In that case, repeat bloodwork and imaging are scheduled to track what’s happening. Importantly, seeing a confirmed pregnancy inside the uterus essentially rules out an ectopic pregnancy, except in extremely rare cases where both occur simultaneously.
Ovarian Cysts and Other Growths
Transvaginal ultrasound is the go-to imaging method for identifying cysts on the ovaries. Most ovarian cysts are functional, meaning they form during a normal menstrual cycle and resolve on their own. The ultrasound can show the size, shape, and internal contents of a cyst, helping distinguish a simple fluid-filled cyst (almost always harmless) from a complex one with solid areas or irregular walls that may need closer follow-up.
The scan also detects uterine fibroids, which are noncancerous muscle growths in the wall of the uterus. It can show how many there are, how large they’ve grown, and where they sit, whether inside the uterine cavity, within the muscle wall, or on the outer surface. This matters because location affects symptoms and treatment options. Endometrial polyps, small growths on the uterine lining, are also visible, particularly when they cause irregular bleeding.
Endometrial Thickness and Cancer Screening
For women experiencing bleeding after menopause, a transvaginal ultrasound measures the thickness of the endometrium, the lining of the uterus. In postmenopausal women, an endometrial thickness of 4 mm or less carries a greater than 99% negative predictive value for endometrial cancer. In other words, a thin lining makes cancer extremely unlikely. A thicker measurement doesn’t mean cancer is present, but it does prompt further testing, usually an endometrial biopsy, to examine cells directly.
In premenopausal women, endometrial thickness fluctuates naturally throughout the cycle, so there isn’t a single cut-off. Your provider interprets the measurement in context with your cycle timing and symptoms.
Fertility Assessments
Transvaginal ultrasound plays a central role in fertility workups. One key test is the antral follicle count, performed early in your menstrual cycle, typically around day 3. During this scan, the doctor or technician counts the small, egg-containing follicles developing on each ovary. These antral follicles measure between 2 mm and 10 mm, and the number visible gives a useful estimate of your remaining egg supply, known as ovarian reserve.
A higher count suggests a larger reserve and a likely strong response to ovarian stimulation medications used in IVF. A lower count, roughly three to six follicles, indicates reduced ovarian reserve. That said, a low count doesn’t reliably predict failure to conceive. It may mean a higher dose of stimulation medication is needed if you pursue IVF. Throughout a fertility treatment cycle, repeat transvaginal ultrasounds track follicle growth so your provider can time procedures precisely.
PCOS Diagnosis
Polycystic ovary syndrome is diagnosed using a combination of symptoms, blood tests, and ultrasound findings. Under the widely used Rotterdam criteria, polycystic-appearing ovaries on ultrasound are defined as either 20 or more follicles per ovary or an ovarian volume greater than 10 cubic centimeters. The scan alone doesn’t confirm PCOS. At least two of three criteria must be present: the ultrasound findings, irregular or absent periods, and elevated androgen levels (signs like acne, excess hair growth, or high testosterone on bloodwork).
IUD Placement and Other Uses
If you have an intrauterine device and experience unusual pain, cramping, or changes in your IUD strings, a transvaginal ultrasound can confirm whether the device is still correctly positioned inside the uterus. It can also detect if the IUD has shifted, partially expelled, or in rare cases, perforated the uterine wall.
Beyond these common uses, the scan can identify fluid collections in the pelvis, help evaluate the cause of chronic pelvic pain, and provide guidance during certain procedures like saline infusion sonography, where sterile fluid is introduced into the uterus for a more detailed view of the cavity lining.
What the Exam Feels Like
The transducer is a slim, wand-shaped probe, narrower than a standard speculum. It’s covered with a protective sheath and lubricating gel before being gently inserted into the vaginal canal. You’ll lie on your back with your knees bent, similar to a pelvic exam position. The technician or doctor moves the wand at different angles to capture images of the uterus and both ovaries. Most people describe the sensation as mild pressure rather than pain, though it can be uncomfortable if you have active pelvic tenderness or certain conditions like endometriosis.
The entire scan typically takes 15 to 30 minutes. Unlike a transabdominal ultrasound, you don’t need a full bladder. In fact, you’re usually asked to empty your bladder beforehand, since a full bladder can push pelvic organs out of the probe’s optimal range. There’s no radiation involved, and results are often discussed the same day or at a follow-up appointment depending on the setting.