Skeletal Survey Calculator 3.1

Clinical-use disclaimer: This calculator supports structured counseling when fetal skeletal dysplasia is suspected. It organizes the skeletal survey, reports objective measurements and ratios, and places the Crane 2024 marker count in context. It does not diagnose a specific dysplasia and does not replace clinical genetics, expert ultrasound, MRI when used, neonatology, or palliative-care counseling when appropriate.

Gestational age + measurements

Stated GA (weeks)

Stated GA (days)

HC (mm)

Head circumference

BPD (mm)

Biparietal diameter

Humerus (mm)

Femur (mm)

Radius (mm)

Ulna (mm)

Tibia (mm)

Fibula (mm)

Thoracic circumference (mm)

Abdominal circumference (mm)

Thoracic circumference percentile (optional)

Required for a complete marker-count result. Enter a percentile from a validated thoracic-circumference nomogram. The Crane 2024 marker is TC < 2.5th percentile; values at or above 2.5 are not positive.

Foot length (mm)

AP mandibular diameter (mm)

Tip: The objective screen counts TC/AC < 0.60, FL/AC < 0.16, and TC < 2.5th percentile. All three must be assessed before applying the published marker-count predictive values. Subjective thoracic findings are reported separately.

Pattern & Marker Screens

1) Thoracic assessment and Crane 2024 marker count

Objective three-marker screen (Crane et al., 2024): TC/AC < 0.60, FL/AC < 0.16, and thoracic circumference < 2.5th percentile.

2024 marker-count evidence and interpretation

Objective markers	Overall cohort	Initial evaluation < 28 weeks	Initial evaluation ≥ 28 weeks
0 positive	NPV 91% for a non-life-limiting outcome	NPV 91%	NPV 91%
1 positive	PPV 50%	PPV 58%	PPV 27%
2 positive	PPV 78%	PPV 90%	PPV 43%
3 positive	PPV 100% (5/5; very small sample)	PPV 100% (3/3)	PPV 100% (2/2)

Individual marker performance in the 96-fetus outcome cohort

Marker	Sensitivity	Specificity	PPV	NPV
TC/AC < 0.60	10% (5/49)	100% (47/47)	100% (5/5)	52% (47/91)
FL/AC < 0.16	84% (41/49)	57% (27/47)	67% (41/61)	77% (27/35)
TC < 2.5th percentile	59% (29/49)	81% (38/47)	76% (29/38)	66% (38/58)

These predictive values came from an enriched tertiary-referral cohort of fetuses with suspected skeletal dysplasia and are not general-population risks. PPV depends on disease prevalence. Individual markers had limited prognostic performance, and evaluation at or after 28 weeks was less reliable. Integrate the complete phenotype, thoracic/rib appearance, serial findings, molecular testing, and neonatal consultation.

Subjective thoracic restriction / pulmonary hypoplasia concern

Clinical modifier only. This selection does not count as one of the three Crane objective markers and does not change the published PPV.

Serial trend (if known)

Rib length (subjective/US pattern)

Thorax shape

2) Bone mineralization + fractures

Skull mineralization

Long bone mineralization

Fractures (select all that apply)

Rib fractures Long bone fractures Callus / healing fractures No fractures seen

Beaded ribs

3) Disproportion pattern (core classifier)

Shortening pattern

Symmetry

Polydactyly

Bowing severity

If present, specify bones below.

Which bones bowed? (free text)

4) Shape-specific long bone features

Metaphyseal changes

Epiphyseal pattern

Femur “telephone receiver” shape

Diaphyseal appearance (optional)

5) Spine / pelvis clues

Spine

Short trunk (overall)

Pelvis/iliac (subjective)

6) Craniofacial markers (beyond jaw index)

Frontal bossing Midface hypoplasia Cleft lip/palate Macrocephaly pattern Micrognathia suspected

7) Associated anomalies

Hydrops Cardiac anomaly Renal anomaly CNS anomaly Abdominal wall defect (e.g., omphalocele) Single umbilical artery Genital anomaly / ambiguous genitalia

Morphology prompts (Head / Thorax / Hand / Foot)

Head

Thorax

Hand

Foot

Results

EMR-ready output

Note: Pattern-based statements are intentionally non-diagnostic and should be confirmed with imaging, genetics, and clinical context.

Design and JavaScript originally created 1/30/2020 by Mark Curran, MD, FACOG. Enhancements: mobile layout + pattern screens + consult-ready EMR text output (non-diagnostic). Version 3.4 adds floating Evaluate and Reset controls and reports objective marker count, gestational age, published predictive value, and an explicit limitation statement in calculated outputs; the separate quick table below is a non-diagnostic differential/prognosis reference aid.

REFERENCES

Prenatally detected skeletal dysplasias — lethality quick table (not exhaustive)

Intended for rapid differential framing and counseling context only; this table is not diagnostic and is not a calculated result. “Life-limiting” generally reflects expected perinatal death without ongoing aggressive life-sustaining intervention, commonly because of severe pulmonary hypoplasia; exceptions occur. Correlate with gestational age, thoracic size, rib morphology, mineralization, serial findings, molecular testing, genetics consultation, neonatology input, and family goals of care.

Condition / group (commonly detected)	Key prenatal ultrasound clues	Thorax	Typical perinatal prognosis	Common gene(s)
Thanatophoric dysplasia	Severe micromelia; (Type 1 bowed “telephone receiver” femurs); macrocephaly; (Type 2 ± cloverleaf skull)	Narrow thorax common	Usually life-limiting	FGFR3
Osteogenesis imperfecta type II / severe OI spectrum	Decreased mineralization; fractures/callus; compressible skull; beaded ribs	Small / hypoplastic	Usually life-limiting	COL1A1/COL1A2; others
Achondrogenesis spectrum	Extreme micromelia; poor ossification; large head; hydrops common	Very small	Usually life-limiting	COL2A1; SLC26A2; TRIP11; others
Hypophosphatasia (perinatal severe)	Marked hypomineralization; short/bowed long bones; fractures may occur	Small	Usually life-limiting	ALPL
Atelosteogenesis spectrum	Severe limb shortening; abnormal bone shape; joint dislocations	Often small	Usually life-limiting	FLNB; SLC26A2 (some)
Campomelic dysplasia	Bowed long bones (esp. tibiae); hypoplastic scapulae; ambiguous genitalia; facial anomalies	Often small	Often life-limiting	SOX9
Short-rib thoracic dysplasia / short-rib polydactyly groups	Short ribs; very narrow thorax; polydactyly common; renal/cardiac anomalies possible	Severely restricted	Often life-limiting	DYNC2H1, IFT140, WDR35, WDR60, IFT172, KIAA0586, TTC21B…
Jeune syndrome (asphyxiating thoracic dystrophy / ATD)	Narrow thorax; short ribs; variable limb shortening; renal/liver disease may appear later	Variable restriction	Variable	IFT140, DYNC2H1, WDR60, WDR34…
Jarcho-Levin / spondylocostal dysostosis spectrum	Short trunk; segmentation anomalies; rib anomalies; scoliosis/kyphosis	Variable	Variable	DLL3, TBX6, MESP2, LFNG, HES7…
Ellis-van Creveld	Short limbs; postaxial polydactyly; congenital heart disease; short ribs may be mild	Usually not lethal	Usually survivable	EVC, EVC2
Achondroplasia (heterozygous)	Later-onset (21–27 w) rhizomelia; macrocephaly/frontal bossing; trident hand	Usually adequate	Usually survivable	FGFR3
Achondroplasia (homozygous / severe phenotype variants)	Earlier onset (15–16 w) rhizomelia; macrocephaly/frontal bossing; trident hand	Severe chest narrowing	Usually life-limiting	FGFR3
Hypochondroplasia	Milder rhizomelia; may be subtle prenatally	Usually adequate	Usually survivable	FGFR3
Diastrophic dysplasia	Short limbs; hitchhiker thumbs; clubfeet; joint contractures	Usually adequate	Usually survivable	SLC26A2
Spondyloepiphyseal dysplasia congenita (SEDC)	Short trunk; platyspondyly; mild limb shortening; possible micrognathia	Variable	Variable	COL2A1
Kniest dysplasia	Short trunk; abnormal epiphyses; limb shortening; facial findings	Usually adequate	Variable	COL2A1
Chondrodysplasia punctata spectrum	Epiphyseal stippling; limb shortening; cataracts/skin findings depending on type	Variable	Variable	ARSE, EBP, PEX7…
Larsen syndrome spectrum	Large-joint dislocations; clubfeet; characteristic facies; limb shortening variable	Usually adequate	Variable	FLNB (classic)
Antley-Bixler spectrum	Craniosynostosis; radiohumeral synostosis; femoral bowing; genital anomalies possible	Variable	Variable	POR; FGFR2
Metatropic dysplasia	Long-bone flaring; short trunk; progressive kyphoscoliosis	Variable	Variable	TRPV4
Robinow syndrome	Mesomelia; vertebral segmentation anomalies; genital anomalies; facial features	Usually adequate	Usually survivable	ROR2, DVL1/3, WNT5A…
Osteopetrosis (severe infantile forms)	Increased echogenicity/density (often subtle); fractures possible; macrocephaly	Variable	Variable	TCIRG1; others
Schneckenbecken dysplasia	Severe micromelia; characteristic pelvis; poor ossification	Very small	Usually life-limiting	SLC35D1
Desbuquois dysplasia Type 1	Severe micromelia; joint laxity/dislocations; characteristic hand findings (extra ossification, delta phalanx, thumb bifidity)	Narrow chest	Often life-limiting	CANT1
Desbuquois dysplasia Type 2	Short limbs; joint laxity/dislocations	Usually adequate	Variable	XYLT1; sometimes CANT1
Opsismodysplasia	Delayed ossification; short limbs; platyspondyly	Variable	Variable	INPPL1
SHOX-related dysplasia spectrum (incl. LWD)	Short long bones; mesomelia may be present; often subtle prenatally	Usually adequate	Usually survivable	SHOX
Smith-McCort / Dyggve-Melchior-Clausen spectrum	Short trunk; platyspondyly; delayed ossification	Usually adequate	Usually survivable	RAB33B; DYM
Mucopolysaccharidosis (severe early forms)	Hydrops; organomegaly; dysostosis features may be subtle prenatally	Variable	Variable	Multiple