A lower-abdomen (pelvic) ultrasound images the bladder, uterus, endometrium and ovaries (or prostate and bladder in men), plus nearby bowel and pelvic blood flow. It detects pregnancy, ovarian cysts, fibroids, pelvic masses, ectopic pregnancy, hydronephrosis and free fluid/ascites. The scan assesses organ size, structure and vascularity to help diagnose pain, abnormal bleeding, infertility or suspected pelvic disease.

On a 3D ultrasound, sex is usually identified from about 18–22 weeks by visualizing external genitali

A 3D pelvic ultrasound is performed with the patient lying on an exam table; gel is applied to the lower abdomen for a transabdominal scan or a small probe is inserted vaginally for a transvaginal scan. The transducer sweeps or captures multiple 2D slices that the machine reconstructs into a 3D image. The test is non‑ionising, quick (about 15–30 minutes) and typically painless.

3D ultrasound provides detailed views of fetal anatomy and can help detect structural abnormalities such as facial clefts, limb and skeletal defects, neural tube and spinal anomalies, and some cardiac or chest defects. It improves visualization of the placenta, uterine anatomy, multiple pregnancies, and fetal surface features (including fetal sex). It complements 2D imaging for diagnosis, surgical planning, and parental counseling.

Abdominal ultrasound commonly detects liver cancers (primary hepatocellular carcinoma) and liver metastases, kidney (renal) tumors, gallbladder and bile-duct lesions, ovarian masses, and some splenic or retroperitoneal tumors. It can suggest pancreatic masses but is less sensitive for pancreas and bowel cancers. Ultrasound finds masses and ascites but may miss small or deep lesions, so CT or MRI are often needed.

A heavy feeling in the lower abdomen can come from bloating, gas, constipation, menstrual cramps or ovulation, urinary tract infections, pelvic inflammatory disease, ovarian cysts, fibroids, early pregnancy, or irritable bowel syndrome. Less commonly a hernia or other surgical condition causes it. Seek medical attention if you have severe pain, fever, persistent or worsening symptoms, abnormal bleeding, difficulty urinating, or signs of pregnancy complications.