Fetal Biometry

Question 0

Menstrual Age aka

Answer 0

Gestational Age

Question 1

1 reason 1st trimester bleed

Answer 1

Subchorionic hemorrhage/implantation bleed

Question 2

Fetal Age aka

Answer 2

Conceptual Age

Question 3

Conception

Answer 3

2 days after ovulation

Question 4

Most accurate meas GA

Answer 4

CRL

Question 5

Viability age

Answer 5

24 weeks

Question 6

YS seen when GS meas

Answer 6

> 8mm

Question 7

YS function

Answer 7

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

Question 8

Yolk Sac

Answer 8

< 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

Question 9

YS resorbs

Answer 9

Week 12

Question 10

Fail to see YS when MSD >____mm = abnormal

Answer 10

12 mm

Question 11

Poor prognostic indicators

Answer 11

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

Question 12

Fetal demise US

Answer 12

Huge sac, hetero embryo

Question 13

MSD

Answer 13

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

Question 14

Double sac sign

Answer 14

Decidua capsularis w/ chorionic villi & decidua vera

Question 15

Anembryonic pregnancy / blighted ovum

Answer 15

GS > 25 mm & no embryo

Question 16

CRL

Answer 16

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

Question 17

Rhombencephalon / Primitive Hind Brain

Answer 17

8-11 weeks

Cystic area in head

Question 18

Should ID embryo when GS >

Answer 18

16 mm

Question 19

BPD

Answer 19

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

Thalamus & CSP are landmarks

Question 20

Oxycephaly

Answer 20

Top of skull is pointy

Question 21

Brachycephalic

Answer 21

Rounded short wider head. Over estimates GA

Question 22

Dolicephalic

Answer 22

Flat long narrow head. Under estimates fetal age.

Question 23

Head circumference

Answer 23

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

Question 24

Cephalic index

Answer 24

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

>85% = brachycephaly
<75% = dolichocephaly

Question 25

AC

Answer 25

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

Question 26

FL

Answer 26

Meas shaft/diaphysis length. Exclude epiphysis.

Perpendicular to beam. Meas femur closest to beam.

Question 27

HL

Answer 27

Less accurate than FL

Question 28

Binocular meas

Answer 28

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

Question 29

Lat Vent

Answer 29

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

Meas perpendicular to LV at post glomus of choroid plexus.

Question 30

CM

Answer 30

Norm = 3-11mm

Question 31

Cerebellum

Answer 31

Corresponds to GA @ 26-24 weeks

Question 32

Nuchal Fold

Answer 32

Meas skin thickness behind occipital bone

> or = 5 is abnormal
Assoc with Downs Syndrome

Question 33

Nuchal Lucency criteria

Answer 33

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

Assoc with ❤️ anomalies & aneuploidy

Question 34

Absent nasal bone

Answer 34

Assoc with Downs Syndrome

Question 35

AMA

Answer 35

Mother 35+yrs ok due date