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First Trimester Ultrasound. Maternal and Child Health Tutorial Sarah Gopman, MD Updated 8-29-04. Learning Objectives. Understand basic scientific principles of ultrasound Learn a systematic approach to the first trimester ultrasound exam

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First trimester ultrasound

First Trimester Ultrasound

Maternal and Child Health Tutorial

Sarah Gopman, MD

Updated 8-29-04

Learning objectives
Learning Objectives

  • Understand basic scientific principles of ultrasound

  • Learn a systematic approach to the first trimester ultrasound exam

  • Apply findings of first trimester ultrasound to pregnancy dating

  • Distinguish between normal and abnormal pregnancies

  • Understand applications of ultrasound in medical and surgical termination of pregnancy

Principles of ultrasound
Principles of Ultrasound

  • Bodily structures reflect sound waves differently depending on the density of the tissue

  • Ultrasound uses high-frequency waves (2–10 MHz) to visualize internal structures

  • The ultrasound transducer both transmits and receives sound waves

  • Sound waves reflected off internal structures are converted into an electrical signal, which is used to generate a two-dimensional image on an oscilloscope screen

Principles of ultrasound1
Principles of Ultrasound

  • The higher the frequency, the better the resolution (i.e. the picture is clearer)

  • However, higher frequency results in less penetration and therefore a shorter field of view

  • This is the principle by which endovaginal US works—the transducer is closer to the object being visualized, compensating for the decreased penetration and conveying the benefits of better resolution

Ultrasound terms
Ultrasound terms

  • Isoechoic—same texture as myometrium

  • Hyperechoic—appears whiter than myometrium

  • Hypoechoic—appears darker than myometrium

  • Anechoic—appears black, similar to urine in bladder (fluid)

Utility of routine early ultrasound
Utility of routine early ultrasound

  • Diagnose early pregnancy and establish accurate dating

  • Verify embryonic/fetal life

  • Determine intrauterine vs extrauterine pregnancy

  • Evaluate number of gestations

  • Determine uterine characteristics

  • Determine adnexal characteristics

When early us is especially important
When early US is especially important

  • Abdominal pain or bleeding in early pregnancy

  • Hx of prior ectopic pregnancy

  • Determine delivery date for repeat c/s

  • Potential to induce labor

    • Hx of pre-eclampsia with prior pregnancy

    • Diabetes

    • Other maternal medical condition, such as SLE, etc

  • Patient considering first trimester genetic screening

  • Patient considering termination of pregnancy

Transabdominal us advantages and disadvantages
Transabdominal US: Advantages and Disadvantages

  • Advantages

    • Provides a “panoramic” pelvic view

    • Noninvasive

    • Easy to learn

    • Simple when findings are present

  • Disadvantages

    • Often requires distended bladder for visualization

    • Expense

    • Unable to detect pregnancies less than 6 weeks’ gestation

Endovaginal us advantages and disadvantages
Endovaginal US: Advantages and Disadvantages

  • Advantages

    • Detects earlier pregnancies

    • Readily combined with pelvic exam

    • Does not need a distended bladder

    • Easy skill to learn

  • Disadvantages

    • Expense of examination

    • Invasive

    • Potential for infection

Screen image endovaginal


cervix in the upper right region

fundus in mid left region

bladder in upper left region

spine to right

Transverse (90 degrees counter-clockwise from longitudinal)

patient’s right side on left of screen

patient’s left side on right of screen

Screen Image—Endovaginal

True relationship b w patient and transducer
True relationship b/w patient and transducer

Pregnancy testing
Pregnancy Testing

  • Implantation occurs 5-7 days after fertilization

  • Trophoblastic cells begin to produce hCG

  • Urine pregnancy test positive at time of missed menses

    • Can detect levels of 25 mIU/ml

  • Serial quantitative hCG testing best performed through same laboratory

Structures of 1st trimester pregnancy
Structures of 1st Trimester Pregnancy

  • Gestational sac

  • Yolk sac

  • Embryo/fetus

  • Presence of cardiac activity

Gestational sac
Gestational sac

  • Earliest visualized structure

  • Seen as early as 30 days from LMP via endovaginal ultrasound

  • Eccentric to endometrial stripe

  • Choriodecidual “double ring” reaction

    • increased blood flow and endometrial thickening

    • not seen if pseudosac of ectopic

  • Chorionic sac contains yolk sac; amniotic sac contains embryo

  • Amnion usually fuses with the chorion at 8-10 weeks (obliterates yolk sac)

Beak sign
Beak Sign

  • The intrauterine fluid collection (or sac) shows a small “beak” that connects with or points toward the uterine cavity line

  • Highly suggestive of fluid collection or pseudo-gestational sac

    (Yeh, 1999)

Yolk sac
Yolk Sac

  • Seen at 5-6 weeks LMP, persists to 11-12 weeks

  • Circular, central anechoic area, measures 3-8 mm

  • Larger than the embryo initially

  • Identifies an intrauterine pregnancy

  • 2/3 of pregnancies with yolk sacs continue

  • Connected to embryo but outside amniotic sac

  • Yolk sac excludes pseudogestational sac


  • Cardiac activity in 6th week when embryo is 1-3 mm

  • 95% of pregnancies with cardiac activity continue

  • Crown rump length (CRL) provides most accurate dating

  • Limb buds observed at 8 weeks and terminology changes from embryo to fetus

Estimating gestational age
Estimating Gestational Age

  • Measurements

    • embryo (crown rump length)

    • if embryo not measurable, use gestational sac

  • Gestational sac measurement

    • Inner margins of sac in 2 or 3 dimensions

    • Estimated age (days) = 30 + mean gs (mm)

    • Gestational sac grows at 1 mm/day

    • Can be visualized as early as hcg of 500 mIU/mL

Discriminatory level
Discriminatory Level

  • hCG level at which all normal gestational sacs should be visualized

  • Value for transabdominal ultrasound = 3600 mIU/ml

  • Value for endovaginal ultrasound = 1500–2000 mIU/ml

Estimating ga by embryo size
Estimating GA by embryo size

Embryonic length (crown-rump length=CRL) measurement

Most accurate ultrasound estimate of GA

Avoid limbs and yolk sac

CRL formula (Goldstein):

estimated age (days) = CRL (mm) + 42

First trimester us part two review of learning objectives
First Trimester US: Part TwoReview of Learning Objectives

  • Understand basic scientific principles of ultrasound

  • Learn a systematic approach to the first trimester ultrasound exam

  • Apply findings of first trimester ultrasound to pregnancy dating

  • Distinguish between normal and abnormal pregnancies

  • Understand applications of ultrasound in medical and surgical termination of pregnancy

Systematic exam
Systematic Exam

  • Longitudinal view (transducer button upright)

    • Go from one side to the other

    • Scan uterus and cul de sac

    • Measure pregnancy if present—magnifystructure being measured!

  • Transverse view (transducer button to left)

    • Go from top to bottom

    • Scan uterus and ovaries

Requirements for standard exam in first trimester per aium
Requirements for “standard exam” in first trimester, per AIUM

  • Evaluate uterus and adnexae for gest. sac

  • Crown-rump length of embryo, if present

  • If no embryo, look for yolk sac and measure gest. sac

  • Gest. sac w/o embryo/yolk sac is not proven IUP

  • Document presence of embryonic heart motion (seen if CRL > or = 5mm) and fetal number

Ultrasound of ovaries
Ultrasound of Ovaries

  • Not always seen

  • Found in transverse view moving probe up and down

    • medial to iliac vessels

    • follicles remain round on all views, whereas blood vessels become tube-like

  • Can measure ovarian size in three dimensions

Ovarian cysts
Ovarian cysts

  • Size and consistency change over time

  • Functional Cysts

    • anechoic; sharp, thin walls

    • Ignore if <3 cm diameter

    • Monitor if >3 cm diameter

    • If >6 cm diameter for 6-12 monthsrefer

  • Corpus luteum cysts

    • Can reach 5 cm diameter

    • Thin-walled

    • Can be seen in various states of resolution

    • Regression by 10 weeks GA

Abnormal pregnancy
Abnormal pregnancy

  • Estimated that only half of fertilized eggs become clinical pregnancies

  • One fourth of clinical pregnancies will have threatened abortion—one-half of these will spontaneously abort

  • Cardiac activity in a threatened abortion has a better prognosis

Us findings and miscarriage
US findings and miscarriage

  • Empty gestational sac

  • Deformed gestational sac

  • Gestational sac low in the uterus

  • Gestational sac or embryo which fails to grow

Abnormal yolk sac
Abnormal yolk sac

  • >10 mm yolk sac diameter

  • Yolk sac not present in 29 mm gestational sac

  • Yolk sac not round

Abnormal embryo
Abnormal embryo

  • No cardiac activity when embryo is 5 mm = poor prognosis

  • Gestational sac >25 mm and no embryo = poor prognosis

Ectopic pregnancy
Ectopic pregnancy

  • 0.5-2% of all pregnancies and increasing

  • Fewer maternal deaths due to earlier diagnosis

  • Location

    • >95% in tube

    • 1-3% in cornual,cervical and abdominal locations

  • Heterotopic pregnancies occur at 1/30,000 but higher in assisted pregnancy

  • Ectopic pregnancy risk factors
    Ectopic Pregnancy: Risk Factors

    • Previous ectopic pregnancy

    • Tubal surgry of any kind

    • Known tubal pathology (sequela of PID)

    • DES exposure

    Cervical ectopic pregnancy
    Cervical Ectopic Pregnancy

    • Occurrence is less than 1% of ectopic pregnancies.

    • Risk factors are multiparity, prior surgical abortion, and instrumentation of cervix.

    • Differential diagnosis is incomplete spontaneous abortion.

    • Morbidity and mortality increased due to profuse bleeding.

    Interstitial cornual pregnancy
    Interstitial (Cornual) Pregnancy

    • Occurrence is 2-4% of all ectopic pregnancies

    • Myometrium surrounds a portion of the growing gestational sac, allowing it to expand painlessly for a relatively long time.

    • Increased morbidity and mortality because of later presentation and massive hemorrhage.

    Findings in ectopic pregnancy
    Findings in Ectopic Pregnancy

    • Diagnostic: sac, fetus, and fetal cardiac activity in the adnexa

    • Suggestive:

      • Absence of intrauterine GS when hCG above discriminatory zone

      • Complex adnexal mass and fluid in the cul-de-sac

      • Failure of hCG to double in 2 days

        • About 10% of ectopic gestations will have have hCG doubling times in the normal range

        • 12% of IUPs will have hCG’s that fail to double in the normal range(Romero et al., 1986 and Kadar et al, 1981).

    Medical treatment of ectopic pregnancy
    Medical Treatment of Ectopic Pregnancy

    • Methotrexate is effective in selected cases (85-95%)

      • <3.5 cm mass

      • HCG <5-10,000 IU/L

    • Mifepristone is not known to treat ectopic pregnancy

    Trophoblastic disease
    Trophoblastic Disease

    • Epidemiology

      • Rare in US., one in every 1000-2000 pregnancies

      • Elsewhere, up to ten times more common

    • Risk Factors

      • Asian heritage

      • Vitamin A deficiency

      • Older or very young gravida

      • Previous trophoblastic disease (2%)

    Presentation of trophoblastic disease
    Presentation of Trophoblastic Disease

    • Hyperemesis is the primary symptom

    • Vaginal bleeding occurs eventually, but not necessarily in the first 8 weeks

    • Bizarre symptoms from metastases

    • HCG levels are usually abnormally high

    Us applications in medical and surgical abortion
    US applications in medical and surgical abortion

    • Errors in evaluation of pregnancy duration are most important cause of abortion complications

    • US can identify uterine abnormalities, such as bicornuate uterus, which could affect surgical procedures

    • Abortion completeness assessed by

      • History

      • Bimanual exam

      • Ultrasound

      • Serum -hCG

    Transverse view of bicornuate uterus
    Transverse view of bicornuate uterus

    Medical abortion mifepristone
    Medical Abortion: Mifepristone

    • A drop in hCG of >50% by 24 hours is consistent with a complete medical abortion (Walker, et al, 2001) (Honkanen et al, 2002)

    • It is possible to perform a medical abortion using Mife/Miso without seeing a gestational sac, but greater vigilance may be needed to detect ectopic and ongoing intrauterine pregnancies. (Schaff)

    7 cases of ectopic pregnancy among 58 950 mab clients
    7 cases of ectopic pregnancy among 58,950 MAB clients

    Ectopic occurrence rate of 0.012%

    • 1 cornual ectopic

    • 1 ectopic with tube adherent to back wall of uterus, giving appearance of IUP

    • 1 patient with no GS seen on TV US, beta hCG was 1,232 mIU/ml, patient given mife and warning signs of ectopic. Same evening, experienced abd pain, went to hospital and ectopic pregnancy diagnosed.

    • 3 patients had pseudosacs that resembled small gestational sacs

    • 1 unknown- records were incomplete


    • Ultrasound is an invaluable but not infallible tool

    • A systematic scan should be performed

    • The entire patient history and presentation should be evaluated

    • HCG tests are useful combined with clinical judgment

    • Providers must find their own comfort level

    Thanks to

    Eric Schaff, MD

    Mary Fjerstad, NP, MA

    Mary Andrews, NP, MSN

    Mary Gatter, MD

    For use of images and slides