EARLY PREGNANCY PITFALLSDr Catherine Magee

Clinical Fellow

Guys and St. Thomas’ NHS

Foundation Trust

CONTENTS

Why / who / when should we scan?

Role of biochemical markers

Scan findings:

Pregnancy of Unknown Location

Ectopic pregnancies

Miscarriage

Difficulties in diagnosis

SCANNING IN THE EARLY PREGNANCY UNIT

Why

Determine the location and viability of a pregnancy

Who

Symptomatic

Reassurance scan

Dating scan

Post miscarriage / termination

When

At presentation

Positive urinary pregnancy test

No need for blood HCG / progesterone prior to scan

BIOCHEMICAL MARKERS

BHCG

Hormone produced by the placental trophoblast

Detected in plasma or urine 8 days post ovulation

Peaks at 8-10 weeks gestation

Trend gives indication of pregnancy viability

Typically doubles over 48 hours in viable intrauterine pregnancies

Not used to establish gestational age

Not used to diagnose location of pregnancy

Used to plan management of ectopic pregnancy

BIOCHEMICAL MARKERS

Progesterone

Hormone produced by ovaries

Causes endometrial lining to thicken after ovulation

Continued production by corpus luteum after fertilisation / implantation

Usually high in viable intrauterine pregnancies, low in failing pregnancies

Not useful in predicting ectopic pregnancies

No need for serial progesterone levels

WHEN SHOULD WE SCAN?

Discriminatory zone for intrauterine pregnancies

Not the case for ectopic pregnancies

Therefore don’t need bloods prior to first scan

PREGNANCY OF UNKNOWN LOCATION

Positive pregnancy test but unable to visualise pregnancy on ultrasound

Pregnancy site not visualised on between 8-31% of scans

Three eventual possibilities:

Viable IUP

Failing pregnancy / miscarriage

Ectopic pregnancy

PUL

Symptoms

Scan findings

Blood in pelvis

Tenderness on scanning

Endometrial thickness

Gestation

Assisted conception

Unknown dates

Irregular cycle

PUL

Must have BHCG and progesterone levels

Follow up as per results

Algorithms

ECTOPIC PREGNANCIES

Pregnancy implanted anywhere outside the endometrial cavity

Most commonly tubal

Incidence 11/1000 pregnancies in UK

2-3% of women presenting to Early Pregnancy Unit

Known risk factors

DIFFICULTIES WITH ECTOPIC PREGNANCIES

Often present with vague / atypical symptoms

Majority will not have known risk factor

Can have with low HCG

If a patient has ‘passed tissue’ – does not rule out ectopic

Endometrium can be of varying thickness

Pseudosac can mimic early gestation sac

Can have other adnexal masses with different pathology

Cervical ectopics can mimic miscarriage

ENDOMETRIAL THICKNESS

EARLY GESTATIONAL SAC VS PSEUDOSAC

Anechoic sac with trophoblastic reaction

Eccentrically located

Blood flow when Colour Doppler applied

Negative sliding sign

Intradecidual sign

Double decidual sign

Irregular

Centrally located in endometrial cavity

Also consider decidual cysts

WHICH ARE EARLY GESTATIONAL SACS?

ADNEXAL MASS

CERVICAL ECTOPIC

Cervical pregnancies are rare, accounting for less than 1% of all ectopic gestations.

Ultrasound criteria for diagnosis

Empty uterine cavity.

A barrel-shaped cervix.

A gestational sac present below the level of the internal cervical os.

The absence of the ‘sliding sign’.

Blood flow around the gestational sac using colour Doppler

CERVICAL ECTOPIC VS. MISCARRIAGE

THE CORPUS LUTEUM

Cyst like structure on ovary

Different appearances / sizes

Hypoechoic cyst

Solid

Haemorrhagic

Classic ‘ring of fire’ when Doppler applied

Can be bilateral

Twin / heterotopic pregnancy

Note also number of embryos transferred

MISCARRIAGE

Delayed / missed

Empty sac with MSD >25.0mm

CRL with no FH >7.0mm

If CRL <7mm with no FH, must repeat TV US in 7 days

Always offer 2nd opinion

Should diagnose on transvaginal scan

If TA scan must have repeat in 14 days

Incomplete / Retained products of conception

Complete

DIAGNOSING MISCARRIAGE

Differences in intra- and inter-observer measurements

2011 study by Pexters et. al

18.8% difference in measurements of gestational sac (inter-observer)

14.6% difference in measurements of CRL (inter-observer)

11.4% difference in measurements of CRL (intra-observer)

Guidelines changed in 2011 to be 100% specific for the diagnosis of miscarriage ie. larger CRL and GS measurements

OTHER DIFFICULTIES

Chorionic bumps

Fibroids

Adenomyosis

Uterine anomalies

COMPLETE MISCARRIAGE?

History of heavy PVB with thin endometrium

Approx 5% of these will actually have ectopic pregnancy

If the first scan, always clarify with biochemical markers and follow up

CONCLUSIONS

Ultrasound is gold standard for diagnosis in early pregnancy

Early Pregnancy Unit is a multi disciplinary team

Be aware of difficulties

If in doubt – 2nd opinion or wait and rescan