Chukwuma Onyeije, MD · Maternal-Fetal Medicine — a structured approach to recognizing, confirming, and counseling atypical fetal genital findings.
📄 Download Provider Cheat SheetDescribes phenotype — what is directly observed on ultrasound or physical exam.
Describes atypical chromosomal, gonadal, or anatomical sex development — a broader diagnostic category that may or may not be present.
Precise, descriptive language keeps the differential open and protects the family from premature labeling.
Prenatal suspicion of atypical genitalia is uncommon in the general obstetric population.
Associated structural and genetic anomalies are frequent once a case reaches an MFM referral center.
Treat a suspected genital anomaly as a sentinel finding warranting full anatomic survey — not an isolated curiosity.
Ultrasound evaluates external phenotype and selected internal anatomy. It cannot, by itself, determine chromosomal or gonadal sex.
External genital differentiation begins near 8–9 weeks and is largely complete by 16 weeks. Diagnostic confidence rises with advancing gestational age.
An operator directly observes external genital anatomy that does not fit a clear male or female pattern.
The sex predicted by cell-free DNA screening does not match the sex suggested by ultrasound.
Either pathway alone is sufficient to trigger confirmatory imaging and a structured evaluation.
Re-image with an expert operator before communicating any impression to the family.
Adjust fetal position, magnification, orthogonal imaging planes, and obtain cine clips before drawing conclusions.
Size · contour · curvature
Labioscrotal fold fusion · urethral position
A systematic, structured description travels better between sonographer, MFM, and the postnatal team than an impression of "male" or "female."
A clue suggestive of hypospadias — not a definitive diagnosis on its own.
A clue suggestive of severe undervirilization — warrants further evaluation, not a label.
Renal/urinary tract anomalies · OEIS complex · cloacal malformations
Cardiac · CNS · abdominal wall · spine
Atypical genitalia is often one finding within a broader multisystem phenotype — a complete anatomic survey is essential.
Genital finding alone, no other structural anomaly identified.
Genital finding accompanied by anomalies in other organ systems.
Sex predicted by genetic screening conflicts with sonographic phenotype.
Androgen excess (e.g., congenital adrenal hyperplasia) · SRY-related testicular development
Disorders of gonadal development, androgen synthesis, androgen action, or anatomic malformation
Prior sex-screening results · vanishing (co-)twin
History of transplant or transfusion · maternal disease
Each of these can independently explain a discordant or unexpected sex result.
A second cfDNA (or similar screening) platform cannot exclude small rearrangements, mosaicism, or a single-gene DSD. A discordant result should escalate to diagnostic testing — not a repeat screen.
Target specific regions efficiently, but may misinterpret mosaicism or microchimerism.
Count reads across the genome, but remain blind to microtranslocations below their resolution limit.
Neither technology is diagnostic for structural or single-gene DSDs.
Predominantly reflects placental and maternal DNA — introducing biological false positives unrelated to true fetal sex.
Evaluates fetal DNA directly, bypassing confined placental mosaicism and maternal microchimerism.
When non-invasive screening contradicts expert ultrasound, change the specimen source to resolve the discrepancy.
Frame the discordance, the differential, and the testing options before any procedure is discussed.
Amniocentesis for fetal DNA analysis is offered to patients who wish diagnostic clarification — the decision remains theirs.
Fetal MRI complements expert ultrasound in select cases — it does not replace a well-performed, targeted sonographic evaluation.
Communicate confirmed findings plainly and specifically.
Distinguish what could occur from what is statistically likely.
Be explicit that screening findings can be wrong, and explain why.
Coordinating this team prenatally allows a unified, prepared postnatal evaluation instead of a fragmented one.
Atypical genitalia alone does not mandate cesarean delivery.
When congenital adrenal hyperplasia is a consideration, select a delivery center prepared to anticipate and manage a neonatal salt-wasting crisis.
Physical exam plus electrolytes and glucose.
17-OHP and other targeted hormone assays as indicated.
Pelvic and abdominal ultrasound.
✗ Is not automatically a "false-positive male" result.
✗ Is not an indication for repeat cfDNA testing.
✓ Is an indication to confirm anatomy, survey the fetus, reconcile the history, counsel, and offer diagnostic testing.
Use structured, descriptive language — not a premature sex label.
Re-image before communicating any impression to the family.
Complete a full anatomic survey — genital findings are often part of a broader phenotype.
Escalate discordant or concerning findings to diagnostic testing, not another screen.
Coordinate MFM, genetics, pediatric endocrinology, and urology/surgery before delivery.
| 1. | Hughes IA, Houk C, Ahmed SF, Lee PA; LWPES/ESPE Consensus Group. Consensus statement on management of intersex disorders. Arch Dis Child. 2006;91(7):554–563. |
| 2. | Lee PA, Nordenström A, Houk CP, et al. Global Disorders of Sex Development Update since 2006: Perceptions, Approach and Care. Horm Res Paediatr. 2016;85(3):158–180. |
| 3. | Speiser PW, Arlt W, Auchus RJ, et al. Congenital Adrenal Hyperplasia Due to Steroid 21-Hydroxylase Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(11):4043–4088. |
| 4. | American College of Obstetricians and Gynecologists. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin No. 226. Obstet Gynecol. 2020;136(4):e48–e69. |
| 5. | Society for Maternal-Fetal Medicine. Clinical guidance on the interpretation and limitations of cell-free DNA screening in discordant or ambiguous fetal sex results. |
Educational content for healthcare providers. Not a substitute for individualized clinical judgment, genetic counseling, or institutional protocols.