UTZ Obstetrics

AOG

Age of Gestation

CRL

Crown-Rump Length; most accurate dating method up to 12 weeks; measured crown to rump in sagittal plane

BPD

Biparietal Diameter; measured at thalamus and cavum septi pellucidi; outer-to-inner calvarial margins

HC

Head Circumference; measured along outer skull margin at same level as BPD

AC

Abdominal Circumference; taken on true transverse plane through stomach, portal sinus, and umbilical vein; used for fetal weight

FL

Femur Length; diaphysis length measured when shaft is perpendicular to beam; reliable after 14 weeks

BPD measurement landmarks

Outer skull table to inner skull table at thalamic level

HC measurement landmarks

Outer skull margins including thalamus and cavum septi pellucidi

AC measurement landmarks

Skin line through stomach, portal vein, and umbilical vein

FL measurement landmarks

Ends of ossified femoral diaphysis excluding epiphyses

Third trimester fetal weight

Estimated from BPD, HC, AC, and FL; normal 2500–4000 g near term

Fetal position

Cephalic (head down) most common; breech or transverse abnormal after 34 weeks

Cephalic presentation types

Vertex, face, brow

Breech presentation types

Frank (hips flexed, knees extended), complete (hips/knees flexed), footling (feet presenting)

Fetal lie

Longitudinal (normal), transverse, oblique

Placenta location

Anterior, posterior, fundal, or lateral; documented at each scan

Placenta thickness

2–4 cm mid-pregnancy; >5 cm thick abnormal (hydrops, diabetes)

Placenta previa

Placenta partly or completely covers internal os after 28 weeks

Placenta accreta spectrum

Abnormal adherence to myometrium; includes accreta, increta, percreta

Placenta abruption

Retroplacental hematoma; hypoechoic or complex collection behind placenta

Placental maturity grades

Grade 0 (uniform echotexture), I (scattered calcifications), II (calcifications with indentations), III (cotyledons, extensive calcification)

Umbilical cord vessels

Normally 3 (2 arteries, 1 vein)

Single umbilical artery

May indicate renal or cardiac anomaly

Cord coiling

Normal; absent or excessive coiling may signal compromise

Velamentous cord insertion

Cord inserts into membranes; vessels unprotected, risk of vasa previa

Battledore placenta

Marginal cord insertion within 2 cm of placental edge

Vasa previa

Cord vessels cross cervical os; risk of rupture and fetal death

Placental lakes

Well-defined anechoic spaces; benign if small and few

Chorioangioma

Benign vascular placental tumor; can cause polyhydramnios or hydrops if large

Amniotic fluid index (AFI)

Normal 5–24 cm (sum of 4 quadrants)

Single deepest pocket (SDP)

Normal 2–8 cm;

Oligohydramnios causes

Renal agenesis, IUGR, PROM, post-term

Polyhydramnios causes

GI obstruction, diabetes, anencephaly, twin-twin transfusion

Biophysical Profile components

Fetal breathing, body movement, tone, AFI, NST; 8–10 = normal

Umbilical artery Doppler

Normal forward diastolic flow; absent/reversed flow = placental insufficiency

Middle cerebral artery Doppler

Low resistance flow; increased flow suggests anemia or hypoxia

Ductus venosus Doppler

Reversed a-wave abnormal; linked to cardiac compromise

Cerebellum measurement

Transverse cerebellar diameter in mm ≈ gestational age in weeks (14–40 wks)

Lateral ventricle normal width

Cisterna magna normal

2–10 mm; enlarged in Dandy–Walker; absent in Chiari II

Nuchal fold thickness

Normal <6 mm (measured 18–22 wks); increased with trisomy 21

Anencephaly

Absent cranial vault; exposed brain tissue; detectable by 12–14 wks

Spina bifida indicators

“Lemon” shaped skull and “banana” cerebellum

Hydrocephalus

Ventricular dilatation; lateral ventricle >10 mm

Holoprosencephaly

Single midline ventricle, fused thalami; facial anomalies

Agenesis of corpus callosum

Absent CSP, “teardrop” ventricles

Cystic hygroma

Septated cystic neck mass; often with Turner syndrome

Cleft lip/palate

Facial discontinuity; best seen coronal view of upper lip

Congenital diaphragmatic hernia

Abdominal organs in thorax; mediastinal shift

Pulmonary hypoplasia

Small chest size; secondary to oligohydramnios or hernia

Cardiomegaly

Cardiac area >1/3 thoracic area; may indicate hydrops or anemia

Fetal cardiac four-chamber view

Normal heart occupies 1/3 thorax; apex points left 45°

Tetralogy of Fallot

Overriding aorta, VSD, pulmonary stenosis, RV hypertrophy

Echogenic intracardiac focus

Small bright spot in ventricle; often benign but marker for trisomy 21

Omphalocele

Midline defect with membrane-covered bowel/liver

Gastroschisis

Right paraumbilical wall defect without covering membrane

Megacystis

Bladder >7 mm before 14 wks; may suggest obstruction

Hydronephrosis

Renal pelvis >10 mm (3rd trimester); mild 5–9 mm

Multicystic dysplastic kidney

Multiple non-communicating cysts; absent normal parenchyma

Renal agenesis

Absent kidneys; severe oligohydramnios; “lying down adrenal” sign

Bladder exstrophy

Absent bladder + anterior wall defect

Hydrops fetalis

Fluid in ≥2 fetal compartments (ascites, pericardial, pleural, skin edema)

Skeletal dysplasia

Short long bones; bowed femurs; thoracic narrowing

Thanatophoric dysplasia

Severe micromelia; cloverleaf skull; lethal

Achondroplasia

Rhizomelic shortening; frontal bossing; trident hand

Osteogenesis imperfecta

Hypomineralized bones; multiple fractures

Clubfoot (talipes)

Foot inverted and adducted; persistent deviation from tibia

Amniotic band syndrome

Fibrous strands attached to fetal parts; causes amputations or deformities

IUGR definition

Estimated fetal weight <10th percentile for GA

Symmetric IUGR

Proportionately small head and body; early insult

Asymmetric IUGR

Head spared; abdomen small; due to placental insufficiency

Macrosomia

EFW >90th percentile; AC disproportionately large

Post-term pregnancy

42 weeks; AFI often low, placenta Grade III

Fetal breathing motion

Seen ≥30 weeks; periodic chest excursions

Fetal tone

Persistent flexion and extension of limbs/spine; part of BPP

Fetal movements

Gross limb/trunk movements observed within 30 minutes

NST (Non-stress test)

Reactive if ≥2 accelerations ≥15 bpm for ≥15 s within 20 min

BPP scoring

2 pts each for breathing, movement, tone, AFI, NST; 8–10 normal, ≤4 abnormal

Normal FHR

110–160 bpm

GS

Gestational Sac; first sign of intrauterine pregnancy at ≈5 weeks; round/oval fluid with echogenic rim

MSD

Mean Sac Diameter; average of length + width + height of GS / 3; correlates with early gestational age

YS

Yolk Sac; first anatomic structure seen within GS; appears ≈5.5 weeks; normal ≤ 6 mm; disappears by 12 weeks

NT

Nuchal Translucency; subcutaneous fluid at fetal neck; measured 11–14 weeks; normal < 3 mm

FHR

Fetal Heart Rate; visible at 6 weeks; normal 110–160 bpm

GS without YS

Abnormal after >8 mm MSD; suggests anembryonic (blighted ovum)

YS without embryo

Abnormal if >20 mm MSD and no embryo

Double decidual sac sign

Normal indicator of intrauterine GS; two concentric echogenic rings surrounding sac

Subchorionic hemorrhage

Hypoechoic crescent adjacent to GS; common early bleed

Ectopic pregnancy

No IUP + adnexal mass ± free fluid; ring-of-fire on Doppler

Molar pregnancy

“Snow-storm” pattern; echogenic mass with multiple small cystic spaces; no identifiable fetus

CRL = 6 mm

≈6 weeks AOG

GS = 10 mm

≈5 weeks AOG

Embryo visible

≈5.5–6 weeks AOG

FHR visible

on transvaginal scan ≈6 weeks

Placenta visible

≈9–10 weeks AOG

BPD = 2.4 cm

≈14 weeks AOG

FL = 1.5 cm

≈14 weeks AOG

AC growth pattern

Increases ≈1.5 cm per week mid-trimester