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Flashcards in Fetal Biometry Deck (36)
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#1 reason 1st trimester bleed

Subchorionic hemorrhage/implantation bleed

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Menstrual Age aka

Gestational Age

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Fetal Age aka

Conceptual Age

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Conception

2 days after ovulation

4

Most accurate meas GA

CRL

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Viability age

24 weeks

6

YS seen when GS meas

>8mm

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YS function

Provide nutrients from trophoblast to embryo
Forms primitive gut
Vitellines arteries & veins
Produces primordial germ cell

8

Yolk Sac

< 6mm, not assoc with gest age
YS attached to embryo via yolk stalk
Only see 2nd YS on US

Abnormal YS > 8mm, solid, echogenic lumen, irreg walls

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YS resorbs

Week 12

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Fail to see YS when MSD >____mm = abnormal

12 mm

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Poor prognostic indicators

CRL without HR. CRL > 7 mm without HR indicates demise

Low HR < 90 bpm

Abnl YS: irreg walls, Echogenic, > 8mm

Discordant Sac Size: GS vs CRL. GS > 25 mm without embryo = failed pg

12

Fetal demise US

Huge sac, hetero embryo

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MSD

Earliest measurement.
< 5 weeks
Low accuracy +- 2-3 wks
Seen when hCg > 500mIu/ml
MSD=(L+W+AP)3
MSD+4= Age

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Double sac sign

Decidua capsularis w/ chorionic villi & decidua vera

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Anembryonic pregnancy / blighted ovum

GS > 25 mm & no embryo

16

CRL

Most accurate
+- 5 days
ID 5.5 weeks
Less accurate > 12 wks

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Rhombencephalon / Primitive Hind Brain

8-11 weeks
Cystic area in head

18

Should ID embryo when GS >

16 mm

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BPD

+- 11 days @ 17-26 weeks
+- 3 wks in third tri
Meas outer to inner, perpendicular to falx, meas through thalamus

Thalamus & CSP are landmarks

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Oxycephaly

Top of skull is pointy

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Brachycephalic

Rounded short wider head. Over estimates GA

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Dolicephalic

Flat long narrow head. Under estimates fetal age.

23

Head circumference

At BPD level
Trace outer edge of calvarium
HC= (BPD+OFD)X1.57

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Cephalic index

CI=(BPD/OFD)x100
Indicates reliability of BPD

>85% = brachycephaly
<75% = dolichocephaly

25

AC

Estimates fetal weight
Indicates growth
HC/AC ratio indicates symmetry

Trvs abdomen at portal umbilical junction. Trace outer skin. May or may not see stomach depending if full. Make sure spine not oblique. May see adrenals. Should not see kidneys or fetal CI.

AC= (long diam + trvs diam ) 1.57

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FL

Meas shaft/diaphysis length. Exclude epiphysis.

Perpendicular to beam. Meas femur closest to beam.

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HL

Less accurate than FL

28

Binocular meas

Useful when BPD is difficult to obtain. Outer distance. Both orbits.

29

Lat Vent

Meas atrium
Doesn't change much from 13-40 weeks
> 10 mm = ventriculomegaly

Meas perpendicular to LV at post glomus of choroid plexus.

30

CM

Norm = 3-11mm

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Cerebellum

Corresponds to GA @ 26-24 weeks

32

Nuchal Fold

Meas skin thickness behind occipital bone

> or = 5 is abnormal
Assoc with Downs Syndrome

33

Nuchal Lucency criteria

+ calipers, 75% of image, fetus mid sag plane, no hyperflexion or hyoerextention

Assoc with ❤️ anomalies & aneuploidy

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Absent nasal bone

Assoc with Downs Syndrome

35

AMA

Mother 35+yrs ok due date