Pelvic/Transvaginal US
- Pelvic ultrasound is done two ways: a transabdominal scan (probe on the belly, full bladder) for the wide overview, and a transvaginal scan (probe up close) for the high-resolution detail. They're a team, not rivals.
- A full bladder is your friend transabdominally — it pushes gas-filled bowel out of the way and acts as a window. Transvaginally, you want the bladder empty.
- Read it in a fixed order every time: uterus (size, endometrium, myometrium), then each ovary, then the cul-de-sac for free fluid. Same checklist, every patient.
- The two findings you must never miss are ovarian torsion and ectopic pregnancy — both are clock-ticking emergencies, and both can look deceptively quiet.
The pelvis is a crowded, gassy neighborhood, and ultrasound is the polite way to knock on the door. No radiation, no contrast, just sound waves bouncing off organs that are otherwise tucked deep behind bowel and bone. The catch is that you have to scan it twice, from two different angles, because no single view sees everything. Let me walk you through how the two halves of a pelvic ultrasound fit together — and the handful of things you're really hunting for.
Two probes, one pelvis
Think of it like photographing a house. The transabdominal scan is the photo from across the street: you see the whole property and how things relate, but you can't read the house numbers. You put a curved probe on the lower belly and you need a full bladder — a fluid-filled bladder acts as an acoustic window, a clear pane of glass the sound waves sail straight through, and it conveniently shoves the gas-filled bowel up and out of the picture. Gas is ultrasound's nemesis; sound waves hit it and scatter into useless static.
The transvaginal scan is walking up onto the porch to read the address. A slim high-frequency probe goes right up against the cervix, just centimeters from the uterus and ovaries. Higher frequency buys you gorgeous resolution but shallow reach — perfect here, because the targets are close. For this one you want the bladder empty, the opposite of before, so it isn't crowding the field.
High frequency = sharp detail but shallow penetration. Low frequency = deep reach but blurrier. That trade-off is the whole reason we use two probes instead of one. If the physics of why feels fuzzy, the Doppler and ultrasound basics page lays the groundwork.
The systematic read
The secret to never missing anything is boring on purpose: trace the same checklist on every single patient.
- Uterus. Measure it, note its orientation (anteverted vs. retroverted — which way it leans), and scan the myometrium for fibroids.
- Endometrium. The stripe down the middle of the uterus. Its thickness changes with the menstrual cycle and matters enormously after menopause, where a thickened stripe raises the question of endometrial pathology.
- Ovaries. Find both. Tucked beside the uterus, studded with little dark follicles like a strawberry with seeds — that speckled look is actually how you recognize an ovary.
- Cul-de-sac. The lowest pocket of the pelvis, behind the uterus. A little free fluid here is normal; a lot is a flag.
Color isn't just decoration
Add Doppler and the gray pictures gain a heartbeat — it shows you where blood is flowing and how fast. This is the difference between a boring cyst and a true emergency, so it earns its keep on almost every pelvic study.
In a woman of reproductive age with pelvic pain, the first question isn't "what's the lesion?" It's "is she pregnant?" A urine or blood pregnancy test reframes the entire scan, because it puts ectopic pregnancy at the top of the list.
The two you cannot miss
Most pelvic ultrasounds are reassuring. But two diagnoses turn a routine scan into a sprint, and both are sneaky.
Ovarian torsion is the ovary twisting on its own blood supply like a dog leash wrapping around a post — choke the vessels and the ovary dies. The classic clue is an enlarged, swollen ovary, often with the follicles pushed out to the rim. Doppler flow can be absent, but here's the trap.
Present arterial flow does NOT rule out ovarian torsion. The ovary has a dual blood supply, and torsion can be intermittent, so flow may persist early or come and go. Torsion is a clinical-plus-imaging diagnosis — if the ovary is big and the patient is doubled over in pain, take it seriously even with a reassuring color box. The dedicated adnexal masses page goes deeper.
Ectopic pregnancy is a pregnancy that implanted outside the uterus, usually in a fallopian tube that can't stretch and eventually ruptures. The reassuring sign is finding a normal pregnancy inside the uterus. The worry is a positive pregnancy test with an empty uterus and perhaps an adnexal mass or free fluid in the cul-de-sac. That combination is an ectopic until proven otherwise.
Positive pregnancy test + empty uterus + free fluid in the pelvis = assume ectopic and act fast. A ruptured ectopic bleeds, and it bleeds quickly. See the early pregnancy and ectopic page for how the numbers (the discriminatory zone) tie it together.
The takeaway
Pelvic ultrasound is two scans that cover each other's blind spots — the wide transabdominal overview and the close-up transvaginal detail — read with the same uterus-endometrium-ovaries-cul-de-sac checklist every time. Do that, layer on Doppler, and always ask whether she's pregnant, and the two true emergencies have nowhere to hide.