OB/Gyn Ultrasound

First Trimester Pregnancy

Urine test for B-hCG has a threshold of 20 IU/L and should detect a pregnancy 1 week post-contraception (3 weeks gestational age)

Progesterone for further evaluation >11ng/ml is assoc with intrauterine pregnancy (sens 91, spec 84) Acad Emerg Med 1998:5, 309)

2% of pregnancies are ectopics, however, symptomatic pts presenting to the emergency department can have rates from 7.5%-13%.

Discriminatory zones for serum B-hCG differ by institution but are usually between 1000-1500.

Pregnancy Loss

Vaginal Bleeding or threatened AB occurs in 25% of all clinically apparent early pregnancies. 40-50% will end in loss of the pregnancy.

Spontaneous AB is the expulsion of a non-viable pregnancy before 20 weeks. Microscopic presence of chorionic villi or obvious products of conception are necessary to make this diagnosis.

Incomplete AB is term for a failed pregnancy in which not all of the products have been expelled.

Pelvic Masses

Anatomy

Uterus in non-gravid state is 6-7 cm long and 3-4 cm in transverse and AP. Located in the center of the true pelvis between bladder and rectosigmoid colon. An anteflexed uterus forms a 90° angle with the vaginal canal. The anterior cul-de-sac lies between the uterus and the bladder and is usually empty or filled with bowel. The posterior cul-de-sac or the Pouch of Douglas, is usually filled with bowel loops. It is the most dependant portion of the intraperitoneal region and therefore the most common site for free pelvic fluid.

TRANSABDOMINAL IMAGING ALWAYS PRECEDES Transvaginal

Transabdominal

Should be performed with a full bladder. The absence of this sonographic window can be overcome in thin women with firm pressure.

Midline sagittal views are the most useful. Scan right above the pubic bone with the marker towards the patients head.

Transvaginal

Empty Bladder

Should see entire midline stripe. If the uterus is not immediately seen, it may be anteverted and the probe should be aimed upwards towards the anterior abdominal wall. The uterus will appear as a relatively hypoechoic structure with thick walls and a well defined border. The endometrial midline stripe is thin during the preovulatory phase and thickens and becomes more echogenic during the secretory phase. The cervix can be examined by pulling the probe back a few cm and aiming the head of the probe towards the patients back. The ovaries lie just lateral and posterior to the body of the uterus.

Ovaries hypoechoic structures containing multiple anoechoic follicles. Internal iliac artery and external iliac vein

Transvaginal coronal. If structures are not easily visualized, press on the patients anterior abdominal wall to bring them close to the probe tip. If structure might be bowel, stay still and watch for peristalsis to confirm.

Normal Early Pregnancy

Weeks

Beta

Vag Probe

Abd Probe

4-5

<1000

Intradecidual Sac (±DDS)

1000-2000

Gestational Sac (±DDS)

5-6

>2000

Yolk Sac

Gestational Sac (±DDS)

10-20000

Heart Tones

Yolk Sac

>20000

Clear Embryo

Embryo

Intradecidual Sac

Small sac completely embedded in the endometrium on one side of the uterine midline, not deforming the midline stripe. There should be focal echogenic thickening around the sac

Gestational Sac

Sonolucent center, thick echogenic ring.

DDS: double-decidual sign. 2 echogenic rings surrounding the sac. Decidua capsularis and decidua vera. Makes IUP very likely, but not 100% sensitive (AJR 1996:167) It is normal to sometimes not be able to visualize the double rings the full circumference of the sac.

Must have at least 5mm of myometrium surrounding the entire sac in both sag and transverse

Yolk Sac

The first definitive sign of an IUP. Symmetric circular echogenic structure at the edge of the sac. Present from 5-12 weeks of gestational age. Should see the yolk sac if the gestational sac is >1 cm. If the gestational sac is >2 cm and empty, then it is indicative of fetal demise.

Fetal Heart Tones

Cardiac activity should be seen with an embryo>5mm, at >6 weeks, or >10000 B-hCG. Examine with M-Mode, not Doppler.

Crown Rump Length

Most accurate test to establish dates. Do not measure the yolk sac.

Ectopics

· More than 40% of ectopics present with B-hCG of <1000.

· The only clinical evidence of spontaneous abortion is the passage of products of conception or chorionic villi.

· Always consider heterotopics in women on fertility meds or those having undergone in vitro fertilization.

· Do FAST Exam if woman is unstable

Definite

Live embryo outside of the uterus

Nonspecific

· Free fluid in the posterior cul de sac

· Empty uterus with beta above discriminatory zone

· Tubal ring-looks like a small gestational sac outside of the uterus.

· Complex mass-cystic and solid components

· Interstitial ectopics can look just like IUPs, only careful scanning will reveal that it lies on the margin of the uterine wall and not in the intrauterine cavity, (2-5% of ectopics)

Pregnancy Loss

· Gestational sac>1 cm without yolk sac is probable, >2 cm is definite.

· Embryos >5 mm should have cardiac activity

· Gestational Sac low in uterus

Variants

Pelvic Masses

Corpus Luteum Cyst-

Leiomyomas

Adnexal Torsion

Finding a normal ovary makes this diagnosis less likely

Gestational Trophoblastic Disease

Cluster of grapes appearance, an intrauterine mass with diffuse hypoechoic vesicles.

Tubo-ovarian abscess

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