Things to look in an ultrasound to understand the sex of the fetus and

bae958f8-0d1a-405c-854c-aa0e1fcfbe48.jpeg

Things to look in an ultrasound to understand the sex of the fetus and then think of various malformations possible

analyse_media

Reading File

Finding Sources

Reading File

Finding Sources

Reading File

Searching PubMed

prenatal diagnosis disorders of sex development ultrasound

Reading Article

PMID: 39798051

Quick answer

Determining Fetal Sex on Ultrasound

Timing matters. External genitalia cannot be reliably differentiated before 12 weeks; by 20 weeks, sex is identifiable in over 98% of cases. A meta-analysis of 28 studies found first-trimester accuracy averages ~85-87% (rising from 69% sensitivity at 11 weeks to 89% at 12 weeks to 96% at 13 weeks), while second/third-trimester accuracy reaches ~92-99% (Amankona et al., Journal of Ultrasound, 2025, PMID 39798051). The scan in your uploaded image is labeled around 9 weeks 2 days gestation - too early for any sex assessment; that would need to wait until at least 12-14 weeks (nub/sagittal-sign technique) or ideally the 18-20 week anomaly scan for confident labia/scrotum visualization.

What to look for on ultrasound (axial and sagittal views of the perineum):

Male: A rounded perineal bulge (scrotum), with the phallus pointing cephalad (upward, toward the head) rather than caudad. In the third trimester, testes may be visible within the scrotum, sometimes with physiologic hydroceles.
Female: Two to four parallel echogenic (bright) lines on the perineum representing the labia majora/minora ("three-line sign"), with the clitoris, if seen, pointing caudad (downward).
Supportive clues: Direction of urine stream during fetal micturition - outward/cephalad favors male, downward favors female (though hypospadias can distort this in males). Uterus can sometimes be inferred indirectly by the bladder-to-rectum distance (>3.3 mm second trimester, >4.7 mm third trimester) in females.
3D/4D ultrasound (as in your images) can help clarify genital anatomy when 2D views are equivocal, though it is a supplement, not a replacement, for careful 2D axial/sagittal assessment.
If the appearance is not clearly one or the other, it should be labeled ambiguous rather than guessed - "avoid assigning gender if uncertain" is a standard teaching point, since real ambiguous genitalia and simple poor visualization (fetal position obscures ~30% of perineal views) can look alike.

Malformations / Differential Diagnoses to Consider

1. Normal but poorly visualized genitalia - the most common reason for uncertainty; not a true malformation.

2. Ambiguous genitalia / Disorders of Sex Development (DSD) - seen in about 1 in 5000 live births. Modern classification (replacing older "hermaphrodite" terms):

Old term	Current term	Description
Female pseudohermaphrodite	46,XX DSD	Virilized XX female (excess androgen) - clitoral enlargement, labioscrotal fusion
Male pseudohermaphrodite	46,XY DSD	Undervirilized XY male - micropenis, hypospadias, bifid scrotum, cryptorchidism
XX male	46,XX testicular DSD	Genotypic female, testicular tissue, male phenotype
XY sex reversal	46,XY complete gonadal dysgenesis	Streak gonads, female external genitalia
True hermaphrodite	Ovotesticular DSD	Both ovarian and testicular tissue (rare)

Congenital adrenal hyperplasia (CAH) is the most common cause (~90%) of virilized 46,XX DSD, usually from 21-hydroxylase (CYP21A2) deficiency; less commonly 11-beta-hydroxylase or 3-beta-HSD deficiency.
Androgen insensitivity syndrome and SRY gene mutations are key causes of undervirilized 46,XY DSD.
Sex-chromosome DSD: Turner syndrome (45,X - streak ovaries) and Klinefelter syndrome (47,XXY).

3. Structural anomalies that mimic or accompany genital ambiguity:

Bladder exstrophy / cloacal anomaly - can distort the perineum enough to obscure normal sex assessment.
Penile agenesis (aphallia) - rare, from failure of genital tubercle development.
Hypospadias / epispadias - urethral opening malposition, can alter urine stream direction and phallic appearance.
Micropenis with an otherwise scrotum-like structure (can be mistaken for female).

4. Discordance between ultrasound-assessed sex and genetic/NIPT sex - consider vanishing co-twin, placental or fetal sex-chromosome mosaicism, or maternal androgen-producing tumor (e.g., Sertoli-Leydig cell tumor) causing virilization of a genetically female fetus.

5. Syndromic associations - ambiguous genitalia can be one feature of broader syndromes (e.g., Smith-Lemli-Opitz syndrome, certain aneuploidies), often accompanied by growth restriction, nuchal edema, or structural anomalies of brain, heart, kidneys, or limbs - so genetic counseling/amniocentesis or NIPT is recommended when genitalia look ambiguous.

Key clinical principle: If gender is uncertain prenatally or even at delivery, formal gender assignment should be deferred until karyotype, hormonal, and imaging (ultrasound first-line, MRI as problem-solver) workup is complete.

Sources: The Developing Human: Clinically Oriented Embryology; Creasy & Resnik's Maternal-Fetal Medicine (Ambiguous Genitalia chapter), p. 546-548; Grainger & Allison's Diagnostic Radiology (Imaging of Ambiguous Genitalia), p. 892; Amankona et al., J Ultrasound 2025 (PMID 39798051).

What do u think based ok the scan uploaded

Looking at the images in your uploaded report page, here's what I can actually tell:

This is an early first-trimester dating/viability scan, not an anomaly scan.

The patient label reads "GA 09W2D" / "09W6D" (around 9-10 weeks gestation) with a measurement noted (~3.19 cm), which is consistent with a crown-rump length (CRL) measurement used for dating, not a genital measurement.
The grayscale (2D) images show the gestational sac and fetal pole/embryo - one image shows a circular sac with the fetal pole, another shows the curled embryo shape (the "hook-like" structure is the curled fetal body/spine, not a genital structure).
The orange-toned images are 3D/4D renderings of the fetal profile - forehead, nose, and body contour - typical of an early 3D rendering package used to show parents a "face" view. These do not capture perineal/genital anatomy.
The dark panel with small text is the measurement/biometry data sheet (LMP, EDD, CRL, heart rate, etc.) rather than an image.

My honest take: there is nothing in this set of images that shows fetal genitalia at all, and at 9-10 weeks that's expected - external genitalia are not distinguishable on ultrasound until at least 12 weeks, and reliable sex determination realistically needs 13-14 weeks (with the nub/sagittal-sign technique) or, more confidently, the 18-20 week anomaly scan when labia, scrotum, and phallus orientation can be properly assessed.

So based on what's shown here:

Sex cannot be determined from this scan - it's simply too early, and none of the frames are angled at the perineum anyway.
No malformation can be assessed from this either - this looks like a routine dating/viability scan (confirming gestational age, fetal pole, likely cardiac activity), not a detailed anomaly survey. Structural and genital malformations (as discussed earlier - hypospadias, ambiguous genitalia, bladder exstrophy, CAH-related virilization, etc.) are typically screened for at the 18-20 week detailed anomaly scan, not at 9-10 weeks.

If you're trying to establish fetal sex or screen for malformations, the relevant scan to look at would be the second-trimester anomaly scan (18-20 weeks) report, not this early dating scan. If you have images from that later scan, I'm happy to look at those instead - that's where genital anatomy and structural malformations would actually be visible.

One caveat: I'm reading a photographed page of a printed report, not the original DICOM images, so fine detail and exact labels may be lost in the photo. For any real clinical interpretation, this should be reviewed with the treating obstetrician/sonologist who has the original scan and full clinical context.

This is a shared conversation. Sign in to Orris to start your own chat.