Ambiguous genitalia refers to external sex organs that do not fit the typical appearance of either male or female anatomy at birth. The clinical term now used is “differences of sex development” (DSD), a designation adopted after an international consensus meeting of pediatric specialists recommended replacing older terminology to reduce stigma and improve standardized care.1Europe PMC. Consensus statement on management of intersex disorders The appearance can range from a slightly enlarged clitoris or partially fused labia to an undervirilized penis with undescended testes, and the causes span genetics, hormones, and sometimes environmental exposures. What makes the topic more interesting than a simple anatomical description is how much it reveals about the biology of sex development itself and how sharply the medical and ethical conversation around it has shifted in recent decades.
How Sex Development Normally Unfolds
For the first several weeks of fetal life, the tissue that will become the genitalia is identical regardless of chromosomes. The same ridge of tissue can become either a penis or a clitoris; the same folds can fuse into a scrotum or remain open as labia. Whether things go down a male or female path depends on a cascade of genetic signals and hormones. In mammals, a gene on the Y chromosome called SRY acts as the master switch for male development. It triggers the undifferentiated gonad to become a testis, which then produces testosterone and other hormones that masculinize the rest of the body.2PubMed. Sry and SoxE genes: How they participate in mammalian sex determination and gonadal development?
SRY does not act alone. It works by switching on another gene called SOX9, which takes over a large portion of the regulatory program. Research in mice has found that SRY and SOX9 share a substantial number of target genes, suggesting SOX9 assumes much of the work after the initial trigger.3Cell Reports. The Sex-Determining Factors SRY and SOX9 Regulate Similar Target Genes and Promote Testis Cord Formation during Testicular Differentiation Meanwhile, a competing set of signals pushes toward ovary formation. Genes like WNT4 and RSPO1 actively promote female development, and without SRY to tip the balance, these pathways take over.4PubMed Central. SRY and the standoff in sex determination Sex determination is less of a default and more of a tug-of-war between competing genetic programs. When something disrupts either side of that contest, the result can be genitalia that fall between the two typical endpoints.
The Most Common Causes
There is no single reason a baby is born with atypical genitalia. The causes are grouped by the underlying chromosomes and what went differently during development.
Congenital Adrenal Hyperplasia
The most frequent cause in babies with XX chromosomes is congenital adrenal hyperplasia (CAH), particularly the form caused by a deficiency in an enzyme called 21-hydroxylase. The adrenal glands of an affected fetus cannot produce cortisol properly, and the biochemical traffic jam leads to overproduction of androgens. Because the ovaries and internal female structures develop normally, the core issue is that excess androgens masculinize the external genitalia before birth. Girls with severe, classic 21-hydroxylase deficiency are born with virilized external genitalia that can range from a mildly enlarged clitoris to genitalia that look nearly male.5Endocrine Reviews. Congenital Adrenal Hyperplasia due to 21-Hydroxylase Deficiency Internally, these babies have a uterus, fallopian tubes, and ovaries. The mismatch between the inside and outside is what makes CAH a classic example of how hormones, rather than chromosomes alone, shape genital appearance.
Androgen Insensitivity Syndrome
On the other side of the equation, some babies with XY chromosomes and functional testes still develop female or ambiguous genitalia because their bodies cannot respond to testosterone properly. Androgen insensitivity syndrome (AIS) results from mutations in the androgen receptor gene, and it produces a wide phenotypic spectrum. Complete AIS leads to entirely female-appearing genitalia despite the presence of testes internally. Partial AIS falls somewhere in between, producing varying degrees of ambiguity.6PubMed. Androgen insensitivity and the evolving genetic heterogeneity The testes make testosterone, but because the receptors in target tissues do not work correctly, the signal never gets through.
5-Alpha Reductase Deficiency
One of the more striking presentations involves babies who appear female or ambiguous at birth but develop male characteristics at puberty. In 5-alpha reductase deficiency, the enzyme that converts testosterone into its more potent form (DHT) is missing or deficient. Because DHT is critical for masculinizing the external genitalia in utero, these XY babies are born with ambiguous genitalia. At puberty, when testes ramp up testosterone production, the higher levels of circulating testosterone can compensate, and the person develops male secondary sexual characteristics like a deeper voice, muscle growth, and further genital virilization.7JCEM Case Reports. 5α Reductase Deficiency—a Rare Cause of Ambiguous Genitalia and Gender Dysphoria Communities where this condition clusters have been studied extensively, and the pubertal transformation has profoundly shaped local understanding of gender.
Chromosomal Mosaicism
Sometimes the chromosomes themselves are mixed. In conditions like 45,X/46,XY mosaicism, some cells carry one set of sex chromosomes and others carry a different set. These individuals can have a wide range of genital presentations depending on which cell populations dominate in which tissues. The gonads may be asymmetric as well, with a streak gonad on one side and a functioning testis on the other.8PubMed Central. Clinical and gonadal features and early surgical management of 45,X/46,XY and 45,X/47,XYY chromosomal mosaicism presenting with genital anomalies
Why CAH Can Be a Medical Emergency
For most babies born with atypical genitalia, the immediate medical priority is not the genital appearance itself. But one scenario genuinely demands urgent attention. The severe “salt-wasting” form of CAH disrupts not only cortisol and androgen production but also aldosterone, the hormone that helps the kidneys retain sodium. Without it, a newborn can develop dangerously low sodium, high potassium, and low blood sugar within the first days or weeks of life.9PubMed Central. Salt-Wasting Form of Congenital Adrenal Hyperplasia: A Case Report This is a life-threatening electrolyte crisis if not caught. In boys with salt-wasting CAH, the genitalia look typical, so the condition might not be suspected until the baby becomes seriously ill. In girls, the ambiguous genitalia serve as an early visual flag that prompts hormone testing.
Clinicians managing salt-wasting crises face a practical tension: steroid replacement therapy needs to start quickly to prevent collapse, but ideally a blood sample for hormonal testing should be drawn first, because starting steroids before testing can obscure the diagnosis and complicate later workup.10PubMed Central. Congenital primary adrenal insufficiency and selective aldosterone defects presenting as salt-wasting in infancy: a single center 10-year experience
How Clinicians Evaluate Atypical Genitalia
When a baby is born with genitalia that do not clearly appear male or female, the initial evaluation involves a careful physical exam, hormone panels, chromosomal analysis, and imaging. Clinicians use standardized grading tools to describe the degree of virilization. The Prader scale grades the spectrum of female virilization (typically in 46,XX children), and the Quigley scale does the same for undervirilization in 46,XY children.11Arab Journal of Urology. Disorders of sexual differentiation: II. Diagnosis and treatment These are descriptive tools, not diagnostic ones. They describe what the genitalia look like but do not tell you why.
The diagnostic heavy lifting increasingly comes from genetic testing. Next-generation sequencing panels that screen dozens of genes simultaneously have become a useful frontline test for pinpointing the molecular cause. In one large international cohort study, a likely genetic diagnosis was identified in about 43% of patients with 46,XY DSD, and the rate climbed to roughly 60% in cases specifically involving androgen synthesis or action.12PubMed. Disorders of sex development: insights from targeted gene sequencing of a large international patient cohort Other centers using targeted gene panels have confirmed that this approach is clinically useful and cost-effective, yielding confirmed diagnoses linked to mutations in genes like AR, SRD5A2, NR5A1, and others.13PubMed Central. Next generation sequencing (NGS) to improve the diagnosis and management of patients with disorders of sex development (DSD) Still, more than half of XY DSD cases currently lack a confirmed genetic explanation, which tells you the field has considerable ground left to cover.
The Surgery Debate
Few areas of pediatric medicine are as ethically charged as the question of whether and when to operate on the genitalia of an infant with DSD. For decades, the dominant approach was to perform “normalizing” surgery early in life, often in the first year, on the assumption that clear-looking genitalia would reduce psychosocial distress for the child and family. That assumption has come under sharp scrutiny.
A growing consensus in ethics literature holds that surgery for atypical genitalia in infants should be delayed until individuals can participate in the decision themselves, except where it is medically necessary.14PubMed Central. A principled ethical approach to intersex paediatric surgeries More recent bioethics work goes further, arguing that clinicians should not perform any nonvoluntary genital surgery on prepubescent children unless it is urgently necessary to protect physical health. Voluntary surgeries in older individuals, by contrast, might permissibly be performed for a wider range of reasons, including self-identity or psychosocial well-being, guided by the person’s own values and preferences.15PubMed. Genital Modifications in Prepubescent Minors: When May Clinicians Ethically Proceed?
Advocates for deferral point out that early surgery is irreversible, that genital sensitivity can be affected, and that the child may later identify with a gender different from the one assumed at birth. On the other side, some families and clinicians argue that the psychosocial burden of visibly atypical genitalia can be harmful in its own right, and that some surgical techniques performed early in life yield better tissue outcomes than those performed later. The evidence on long-term results is mixed enough that the debate remains genuinely unresolved.
What Long-Term Outcome Studies Actually Show
The data on surgical outcomes are improving but still limited. One study looking at long-term results of feminizing genitoplasty in DSD patients found that genital sensitivity to mechanical and vibratory stimuli was similar to control groups in women with CAH. No women with CAH in that cohort experienced overall sexual dysfunction. Notably, about 89% of patients in this study said they preferred having had surgery during childhood, and 97% were satisfied with their surgical outcomes.16PubMed Central. Long-term Outcomes of Feminizing Genitoplasty in DSD: Genital Morphology, Sensitivity, Sexual Function, and Satisfaction However, these findings need context. The same study found that non-CAH DSD patients showed impaired detection of light touch compared to controls.17Journal of the Endocrine Society. Long-term Outcomes of Feminizing Genitoplasty in DSD: Genital Morphology, Sensitivity, Sexual Function, and Satisfaction And separate reviews have documented that older surgical techniques, particularly clitoral recession and clitorectomy, can be associated with clitoral pain or decreased sensation.18PubMed. Surgical outcomes and complications of reconstructive surgery in the female congenital adrenal hyperplasia patient: What every endocrinologist should know
This mix of findings is part of what makes the surgery debate so difficult to resolve definitively. A high satisfaction rate in one cohort does not settle the question for all patients, especially given that surgical techniques have changed over time and that outcome studies tend to capture people who stayed in follow-up care, potentially missing those who were dissatisfied and disengaged.
Gender Identity and Prenatal Hormones
A question families often have is whether a child born with ambiguous genitalia will identify as male or female, and whether that can be predicted from the anatomy or the underlying condition. The honest answer is that prediction is unreliable, which is part of why sex assignment in these cases is handled more cautiously now than it was a generation ago.
Research on girls with CAH provides some insight into how prenatal androgen exposure interacts with gender identity. In a study that administered a gender identity interview to 43 girls with classical CAH, about 88% had scores overlapping with those of unaffected girls. On individual items like discomfort as a girl or wishing to be a boy, girls with CAH were similar to controls. However, the average score across the group was intermediate between control girls and girls identified as tomboys. The study concluded that moderate androgen excess early in development produces a small increase in the risk of atypical gender identity, but that this risk cannot be predicted from genital virilization or from the age at which surgery was done.19The Journal of Clinical Endocrinology & Metabolism. Effects on Gender Identity of Prenatal Androgens and Genital Appearance: Evidence from Girls with Congenital Adrenal Hyperplasia
The takeaway for families is that most children with DSD will develop a gender identity that aligns with the sex they were raised as, but a minority will not. No physical feature at birth reliably tells you which group a particular child will fall into, which is another reason the ethics conversation has moved toward preserving options and avoiding irreversible decisions when possible.
Why Multidisciplinary Care Matters
The evaluation and management of DSD is not something any single specialist can handle alone. International guidelines and clinical recommendations consistently call for multidisciplinary teams that bring together endocrinologists, urologists or surgeons, geneticists, psychologists, and social workers.20PubMed Central. Multidisciplinary care for individuals with disorders of sex development The reason is straightforward: the diagnosis involves genetics, the potential emergency involves endocrinology, any surgical decisions require specialized surgical skill, and the psychosocial dimensions require professional support for both the child and the family.21PubMed. Evaluation and management of disorders of sex development: multidisciplinary approach to a complex diagnosis Access to these teams varies widely by geography and healthcare system, and families in rural or under-resourced areas may need to travel to academic medical centers for comprehensive evaluation.
Internal Anatomy Does Not Always Match the Outside
One underappreciated aspect of DSD is that the internal reproductive structures can tell a completely different story from the external genitalia. The internal ducts develop from two separate precursor systems: the Müllerian ducts (which become the uterus, fallopian tubes, and upper vagina) and the Wolffian ducts (which become the vas deferens, epididymis, and seminal vesicles). Normally, only one set persists. In typical male development, the testes produce anti-Müllerian hormone (AMH), which causes the Müllerian ducts to regress.
In a rare condition called persistent Müllerian duct syndrome (PMDS), males who are otherwise normally masculinized externally retain a uterus and fallopian tubes internally because of a deficiency in AMH or a defect in its receptor.22PubMed Central. Persistent Müllerian duct syndrome: A case report and review The genetic basis has been mapped: a specific 27 base-pair deletion in the AMH type II receptor gene is the most common mutation responsible.23Human Molecular Genetics. A 27 Base-Pair Deletion of the Anti-Müllerian Type Ii Receptor Gene is the Most Common Cause of the Persistent MüLlerian Duct Syndrome PMDS is often discovered incidentally during surgery for an undescended testis or a hernia. The external genitalia may look entirely typical, which is a reminder that DSD is not always visible at birth.
Environmental Exposures and Genital Development
Beyond genetics and intrinsic hormonal disorders, there is a separate line of research looking at whether environmental chemicals can interfere with genital development. Endocrine-disrupting chemicals (EDCs) are substances that mimic or block hormones, and some studies have investigated whether maternal exposure to these compounds raises the risk of genital anomalies in offspring. One study found an association between elevated maternal plasma levels of the pesticide hexachlorobenzene and the development of hypospadias (where the urethral opening is on the underside of the penis) in sons, though the researchers cautioned it was based on a limited number of cases.24PubMed. Maternal exposures to endocrine disrupting chemicals and hypospadias in offspring
The environmental endocrine disruption field is large and contentious. Individual studies tend to be small, and it is hard to disentangle one chemical exposure from the many others a pregnant person encounters. The evidence is suggestive enough to keep researchers interested but not strong enough to draw firm conclusions about specific chemicals causing specific genital malformations in humans. Regulatory agencies monitor this research area, but no single compound has been definitively identified as a major cause of ambiguous genitalia in human populations.
Lessons from Other Species
If you think of genital development as a strictly binary switch, the animal kingdom will quickly correct you. Several mammalian species naturally develop genitalia that would look “ambiguous” by human clinical standards. The most famous example is the spotted hyena, whose females develop a pseudopenis and pseudoscrotum, lack an external vaginal opening, and urinate, mate, and give birth through an elongated clitoris.25PubMed. The Biology and Evolution of Fierce Females (Moles and Hyenas) Female talpid moles, meanwhile, develop ovotestes that produce testosterone and external genitalia that closely resemble those of males.
Research on hyenas has been particularly illuminating because it challenges the assumption that all genital masculinization is driven by androgens. Anti-androgen studies in spotted hyenas showed that blocking androgens did not fully prevent clitoral enlargement, suggesting other developmental mechanisms are at work.26PubMed Central. Development of the External Genitalia: Perspectives from the Spotted Hyena (Crocuta crocuta) These findings are a useful reminder that the biology of genital development is more flexible and variable across mammals than the human clinical framework sometimes implies. The human binary of “normal male” and “normal female” genitalia is a practical clinical reference point, not a law of nature.