1st Trimester

AIUM/ACOG/ACR Guidelines Transabdominal and/or transvaginal imaging Appropriate labeling required Uterus, including the cervix and adnexa, to evaluate for

the presence of a gestational sac If a gestational sac seen, its location documented Gestational sac evaluated for presence or absence of

yolk sac or embryo Crown-rump length should be recorded Presence or absence of cardiac activity recorded

http://aium.org/resources/guidelines/obstetric.pdf

1st Trimester

AIUM/ACOG/ACR Guidelines Fetal number reported In multiple gestation, amnionicity and chorionicity

documented Fetal anatomy appropriate for first trimester (unspecified) Appearance of the nuchal region Uterus, cervix adnexal structures, cul-de-sac evaluated

presence, location and size of adnexal masses presence and size of leiomyomata free fluid

http://aium.org/resources/guidelines/obstetric.pdf

1st Trimester

Establishing age of the pregnancy For clinical (US) purposes, the first trimester is 2 weeks

0 days to 13 weeks 6 days The terms menstrual age and gestational age are

equivalent Embryonic age starts at fertilization (2 weeks gestational

age), concludes at the end of the 10th week (12 weeks gestational age) and is used by embryologists to describe human development, but is not useful in clinical practice

1st Trimester

Pregnancy Dating Gestational age based

on time elapsed from start of last menses

Reported in weeks plus days

Embryonic age based on date of fertilization - always 2 weeks less than gestational age

1st Trimester

Maternal Serum hCG2 weeks 0 days to 3 weeks 0 days

1st Trimester

3 weeks 0 days

3 weeks 2 days

4 weeks 0 days

1st Trimester

4 weeks 0 days 5 weeks 0 days

1st Trimester Gestational Sac

Often visible at 3 mm (4 weeks 6 days age)

Thick echogenic rim (chorion)

Intradecidual sign Diameter reported as the

average of three measurements

Enlarges approximately 1 mm mean diameter per day

1st Trimester

Yolk Sac Visible when GS is 10

mm (5 weeks 4 days) First unequivocal sign of

intrauterine pregnancy Resides in the extra-

embryonic space (coelom)

Measurements not useful

1st Trimester

Embryo Visible at approximately

3 mm (5 weeks 6 days) Adjacent to yolk sac Grows at approximately

1 mm per day

1st Trimester

Embryo (Crown-Rump Length)

Best US predictor of gestational age between 7-12 weeks

Useful up to 14 weeks

1st Trimester

Amnion Visible between 6 and 7

weeks Enlarges to obliterate the

extra embryonic coelom and “fuses” to the chorion by 16 weeks

1st Trimester

Embryonic Heart Activity

Visible when CRL is as small as 3 mm (5 weeks 6 days)

Rate starts very slow, and exceeds 160 in normal early pregnancy

Documentation with m-mode or cine preferable to Doppler

1st TrimesterComplications

Criterion “Old” Standards “New” Standards

Gestational sac mean diameter

If >20 mm mean diameter and empty

If >25 mm mean diameter and empty

Yolk sac If absent when GS is >10 mm

If absent when GS is >20 mm

Heart activity If absent when GS is >16 mm or CRL >5 mm

If absent when CRL >7 mm

Ultrasound Obstet Gynecol 2011:38:489

Ultrasound Predictors of Abnormal 1st Trimester Pregnancy

1st TrimesterComplications

Threatened abortion (miscarriage) - vaginal bleeding prior to viability

Inevitable abortion – abnormal gestational sac with no live embryo and dilated cervix

Missed abortion (retained products of conception) – embryo is dead for at least 8 weeks but no passage of tissue

1st TrimesterComplications

Extra-chorionic (subchorionic) hematoma

Between chorion and uterine wall (decidua)

Common in asymptomatic patients

Some correlation of size with clinical outcome

Size measured in 3 orthogonal dimensions

1st TrimesterComplications

Extra-chorionic (subchorionic) hematoma

Hematoma usually has low level echos

Because hematoma is extravascular, there is no flow (unlike placental venous sinus)

1st TrimesterComplications

Extra-chorionic (subchorionic) hemorrhage

But color Doppler is misleading because placental vascular sinuses have flow velocity below the threshold of most Doppler instruments

Hematoma is differentiated from a venous sinus with high resolution grey scale

1st TrimesterComplications

Ectopic Pregnancy Most common in assisted

reproduction (IVF etc.) Presentation most common

in 1st trimester Absence of intrauterine

gestational sac is key Presence of an intrauterine

gestational sac does not exclude an ectopic

Presence of blood in peritoneal cavity (hemoperitoneum) helpful but not always present

1st TrimesterComplications

Tubal Ectopic 80% of ectopics in ampula

or fimbrae Hematoma in the tube

(hematosalpinx) is subtle and must be actively searched for

1st TrimesterComplications

Interstitial Ectopic 3% of ectopics Presentation commonly in

early 2nd trimester Implantation in the tube

between the between isthmus and endometrial cavity

US findings are a gestational sac adjacent to the uterus with absent or thin (<5 mm) myometrium

1st TrimesterComplications

1st TrimesterMultiple Gestation

Twins (“high risk”) Perinatal mortality rate

of dizygotic (fraternal) twins 3-7x singletons

Perinatal mortality rate of monozygotic (identical) twins 2-5x times dizygotic twins

Dichorionic diamniotic Monochorionic,

diamniotic Monochorionic,

monoamniotic

1st TrimesterMultiple Gestation

Dichorionic Complete chorion

around each twin Easy diagnosis up to

12 weeks – chorion is thick and echogenic relative to amnion

Twin “peak” sign

1st TrimesterMultiple Gestation

Monochorionic Diamniotic

1st TrimesterMultiple Gestation

Monochorionic Monoamniotic

1st TrimesterChallenge