OB ultrasound

The plane, and which way is up

Transvaginal, sweeping the uterus in sagittal and transverse, then each adnexa and the pouch of Douglas; transabdominal and the right upper quadrant when free fluid is suspected.

Look for, in order

1. Empty uterus, or a thin decidua or a pseudosac (central, no double ring), in a woman with a positive test.
2. An adnexal mass separate from the ovary: an inhomogeneous mass (the blob sign) or a ring with an echogenic rim (the bagel sign), with or without a yolk sac or embryo inside.
3. Free fluid: a little in the pouch of Douglas is common; echogenic fluid, or fluid reaching Morison's pouch, means haemoperitoneum.
4. The corpus luteum on the ovary is not the ectopic; it moves with the ovary when the probe presses.

What normal looks like

No intrauterine sac with an hCG above the discriminatory level, or an adnexal mass with a positive test, is ectopic until proven otherwise. A definite intrauterine pregnancy almost always excludes it, except after assisted reproduction.

Trap. A pseudosac in the cavity has fooled many: it is central, lacks the double decidual ring, and never contains a yolk sac.

Describe it in this order

1. The plane and the approach (transabdominal or transvaginal)
2. Location of the pregnancy: in the uterus or not
3. Number: singleton or multiple, and chorionicity
4. Viability: cardiac activity
5. Dating or growth: the measurement that fits the stage
6. Fetal anatomy, placenta, cord, fluid, cervix, as the stage allows
7. Adnexa and free fluid
8. Then, and only then, the impression