Early pregnancy assessment(first trimester scan)

Dr Shuhaila AhmadAssociate ProfessorFeto-Maternal Unit

UKM Medical Centre

04/21/23

Scope of the lecture

• Importance of early pregnancy scan• Viable pregnancy• Non-viable pregnancy

– Miscarriage– Ectopic– Molar pregnancy

• Others – Multiple pregnancy– Nuchal translucency

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Importance of EP scan

• Determine:– Site of pregnancy– Gestational age– Viability– Fetal number– Pathology in the uterus and adnexae

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Ectopic pregnancy Intrauterine pregnancy

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Pregnancy with corpus luteal cyst

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Viable pregnancy

• Calculate gestational age using LMP• Scan the whole uterus and adnexae

systematically• Identify the IUGS

– Anechoic area within the uterine cavity– TVS : 4.5 – 5 weeks– Ensure not pseudogestational sac:

• Must see the throphoblastic rim around the GS• Identify the yolk sac

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Gestational sac

Trophoblastic rim

TVS

TAS

• If TVS: – fetal echo should be

present by 16mm– Presence of yolk sac

does not guarantee viable fetus.

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Yolk sac

Fetal echo

Gestational age

• Most accurate is the crown rump length• Least biological variation• Early gestation is better as at late gestation,

the fetus assumes flexion attitude• Beware not to include yolk sac into the

measurement• Wrong measurement may cause wrong EDD

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Gestational age

• Crown-rump length– Get the sagittal view in longest

image of the fetus– Enlarge the image to nearly 70% of

the monitor– Ensure the fetus in neutral

position– Measure from the highest point in

the head to the bottom end.– Do not include the legs– Do at least twice

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Which image is good for measuring CRL?

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Longest image but not sagittal

Longest axis, sagital view but the fetus is in flexion

Fetal viability

• Must be able to see pulsation– If unsure, use M mode

or colour doppler– Should be present if CRL

is 2-4mm– If > 5mm, no FH activity

may mean missed miscarriage

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Important discriminatory values

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Parameters suggestive of viable pregnancy

TAS TVS

Serum βHCG and presence of IUGS

6000 IU/L 2000 IU/L

Mean diameter of GC and presence of yolk sac

NA 8mm

Mean diameter of GC and presence of fetal echo

25mm 16mm

Mean fetal length (CRL) and presence of fetal heart activity

10mm 5mm

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Ectopic pregnancy

• Definition:– Pregnancy that is not present within the inner

lining of the uterus– 95% in the fallopian tubes

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Ultrasonographic features

• Empty uterus• Free fluid the POD• # complex mass / GS in

the adnexae

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U

Molar pregnancy

• Excessive pregnancy symptoms

• Uterus maybe palpable in first trimester

• Usually no fetal echo• Cavity filled up with

multiple sonolucent areas = snow storm appearance

• Presence of multiple theca lutein cysts in the ovaries

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Multiple pregnancies

• Determine number of fetuses• Determine chorionicity

– MC : “T” sign– DC : “λ” sign

• Determine viability• Determine gestational age

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Number of fetuses

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Chorionicity

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Nuchal translucency

• Between 11 to 13+6

weeks• About CRL of 45-84mm• Mid sagittal view of the

head• Just chest and the head

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Key points

• Determine LMP and gestational age• Identify uterus, adnexae and cervix• Identify site if gestational sac• Confirm viability and numbers• Determine gestational age by measuring the fetus

– Identification by TAS is delayed by I week compared to TVS

• Do not hesitate to proceed to TVS if needed• It will NOT increase bleeding or risk of miscarriage

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Thank you and

Good Luck for the hands on session 04/21/23