Madtown Sono

Introduction to First Trimester Pregnancy/Pelvic Ultrasound

Objectives

  1. Identify the goals for the first trimester pregnancy POCUS for the Emergency Provider.
  2. Name the earliest findings of intrauterine pregnancy for the Emergency Provider.
  3. Walk through the steps of performing the transabdominal pelvic POCUS exam.
  4. Walk through the steps of performing the transvaginal pelvic POCUS exam.
  5. Name the views that are required when performing a first-trimester POCUS exam.

Introduction to First Trimester Pregnancy/Pelvic US (presented by Dana Resop, MD)

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Check your knowledge!

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Name several causes of bleeding/pain in early pregnancy.

  1. Implantation
  2. Miscarriage/abortion
  3. Subchorionic hemorrhage
  4. Ruptured ectopic
  5. Heterotopic pregnancy

True or False: Absent IUP on POCUS is highly sensitive for ectopic pregnancy.

True!

The study by Stein et al (2010) determined that an absence of IUP on US was 94-99% sensitive for ectopic pregnancy

True or False: Ectopic pregnancies cannot happen at low HCGs (<1500).

False!

Ectopic pregnancies can happen at ANY b-hCG level (1/10 rupture at <100, and 1/3 rupture at <1000).

Name the three goals (relevant to the ED provider) when performing a first-trimester ultrasound scan.

Three goals:

  1. Find the uterus
  2. Identify a pregnancy in the uterus (IUP or not)
  3. Identify uterus around the pregnancy (evaluating for interstitial pregnancy)

Name the most common location for an ectopic pregnancy to occur.

The fallopian tube! 95% of ectopic pregnancies occur here.

Ectopics may also occur in a variety of other places;

  • Cervix
  • C-section scars
  • Abdominal
  • Ovarian
  • Corneal/interstitial

True or False: When performing a transabdominal pelvic exam, the bladder should be full.

True!

A full bladder can help to more easily identify and visualize the uterus and IUP.

Also consider using a linear probe in thinner patients to evaluate for potential IUP.

True or False: When performing a transvaginal pelvic exam, the bladder should be empty.

True!

When performing a transvaginal exam, the bladder should be empty (can displace the uterus and make more difficult to see)

How do we define an intrauterine pregnancy?

In Emergency Medicine, an intrauterine pregnancy is defined as a gestational sac AND a yolk sac.

This occurs around the 5-6 week timeframe.

True or False: Transabdominal ultrasound should always be performed prior to a Transvaginal ultrasound.

True!

If an interuterine pregnancy is seen on transabdominal views, then a transvaginal view is not necessary.

Name the findings of an interstitial (corneal) ectopic pregnancy.

These are pregnancies that appear to be intrauterine, but are not centrally located within the uterus.

Measure the endomyometrial mantle (the distance from the edge of the gestational sac to the external uterine wall)

  • A measurement <5-7mm is concerning for an interstitial ectopic pregnancy
  • A measurement >7-8mm is more reassuring (with increased sensitivity) for a normal intrauterine pregnancy

Walk through the process of measuring the fetal heart rate

Steps:

  1. Ensure your machine is first set to OB settings!
  2. Using M-mode, place the M-mode line through the heart beat.
  3. Click M-mode again to activate M-mode.
  4. Click ‘Calc’ and use your calipers to measure one heartbeat

A normal fetal heart rate is usually 140-180 beats per minute.

Do NOT use Doppler in early pregnancy to evaluate for fetal heart rate!

Name various methods you can use to estimate gestational age.

Methods for estimating gestational age:

  1. Gestational sac
  2. Crown-rump length (preferred)– measure from the top of the fetus to the bottom of the fetus
  3. Femur length (later in pregnancy)
  4. Biparietal diameter (later in pregnancy)

True or False: The first views through the uterus should be to evaluate for pelvic free fluid.

True!

We recommend that your first few scans through the uterus/pelvis should be to evaluate for free fluid in the abdomen!

A small amount of free fluid may be physiologic, but large puddles of fluid are ectopics until proven otherwise!

Don’t forget to add in the right upper quadrant view if there is high suspicion for ectopic pregnancy.