Ambiguous Genitalia

Ambiguous genitalia is a morphologic diagnosis, with various underlying genetic and hormonal aetiologies. Congenital adrenal hyperplasia (CAH) is the most common cause of ambiguous genitalia; timely diagnosis in the postnatal period is important because of the life-threatening consequences of the classic salt-wasting form. In cases of ambiguous genitalia, invasive diagnosis with chorionic villus sampling (CVS) or amniocentesis can be helpful in reconciling ultrasound (US) findings, determining genetic sex, and diagnosing CAH. Karyotypic results do not always determine sex assignment, given the complex hormonal and social issues involved in sex determination.

While not of primary focus for the medically minded sonographer or sonologist, sex determination is often the most important question for parents during a fetal ultrasound examination. Sex determination, however, can be medically important in the diagnosis of zygosity or chorionicity in multiple gestations, for counseling regarding X-linked diseases, and in cases of ambiguous genitalia. The diagnosis of ambiguous genitalia, which has various causes, can be confusing for any specialist. Uncertainty in the ability to assign a fetal sex can be traumatizing for parents. Attention in explaining and investigating the findings and the differential diagnosis is critical. For both medical and psychological reasons, ambiguous genitalia in a newborn require timely diagnosis and management

Ambiguous genitalia refer to the unclear appearance of the fetal external genitalia, leading to unsuccessful phenotypic determination of fetal sex. In essence, there is confusion between the presence of a clitoris or penis and between the presence of a scrotum or labia. Other terms used include: intersex fetus or fetal genital anomaly. “Ambiguous genitalia” is actually a physical or morphologic diagnosis with various different underlying causes. Disorders of sexual development (DSDs) are divided into five classifications according to the Lawson Wilkins Pediatric Endocrine Society and the European Society for Pediatric Endocrinology (Table 1); ambiguous genitalia can fall within any of these classes.

Table 1: Disorders of sexual development (DSDs)

The incidence of the condition is estimated approximately 1 in 5,000 births. The frequency of the most common cause of ambiguous genitalia, classic congenital adrenal hyperplasia (CAH), is estimated to be 1 in 15,000 births.

The external genitalia become differentiated at approximately 9 weeks of gestation and genital development is typically complete by 12 weeks for females and 14 to 16 weeks for males. Successful morphogenesis of the external genitalia depends on dihydrotestosterone (DHT) exposure for males; in females, vulvar and vaginal differentiation is not hormone-dependent. Without DHT action (because of either a lack of DHT or a failure of DHT to function), a 46-XY fetus could have phenotypically female external genitalia. On the other hand, androgen exposure before 12 weeks of gestation can cause labial fusion or a virilized urogenital sinus, whereas exposure after 12 weeks typically causes only clitoromegaly and labial enlargement (scrotalization). Androgen exposure may occur from maternal ingestion, maternal or fetal ovarian or adrenal tumors or placental P450 aromatase deficiency.

The most common cause of ambiguous genitalia is congenital adrenal hyperplasia (CAH). CAH is a sexual development’ disorder of a genetically female fetus (leading to masculinization of the female fetus) caused by an enzymatic deficiency that disrupts steroidogenesis. In 90% of cases, the deficiency is in CYP21 (21-hydroxylase), which causes an excess of 17-hydroxyprogesterone. Excess 17-hydroxyprogesterone is shunted toward the androgen production pathway of steroidogenesis. Male fetuses remain unaffected with the exception of possible hyperpigmentation and penile enlargement. The shunt also reduces aldosterone and cortisol production, which can produce life-threatening salt-wasting (hyponatremia and hyperkalemia) in the neonatal period. Counseling is demanding and should be offered by experienced specialists.

On the basis of the cause, the condition is divided into three categories:

1. True hermaphrodite: both ovarian and testicular tissue are found within the same gonad. The karyotype is female 46-XX, but there is a chromatinic material from the Y chromosome.
2. Female pseudohermaphrodite: virilized females with normal female karyotype and ovarian gonadal tissue. The causes include congenital adrenal hyperplasia (1 in 15,000), ingestion of androgens by the mother and maternal virilizing tumors.
3. Male pseudohermaphrodite: under virilized males with normal male karyotype and testicular tissue. The causes include inadequate synthesis of testosterone or the presence of an androgen receptor defect.

Most mild cases are expected to be isolated. In general the condition is mostly associated with facial clefts and cardiac defects. However, the condition can be part of a chromosomal abnormality, mainly trisomy 13, triploidy and 13q syndrome. Ambiguous genitalia can also be part of multiple abnormalities seen in syndromes such as Smith-Lemli-Opitz syndrome (autosomal recessive), Prader-Willi syndrome (de novo, imprinting), velo-cardio-facial/DiGeorge syndrome (autosomal dominant, mainly de novo) or WAGR syndrome (sporadic). Additional findings in Smith-Lemli-Opitz syndrome include microcephaly, cardiac, renal and gastrointestinal defects, syndactyly and polydactyly. Additional findings in Prader-Willi syndrome include hypotonia and polyhydramnios. Additional findings in velo-cardio-facial syndrome include heart, craniofacial and CNS defects. Additional findings in WAGR syndrome include Wilms tumor, aniridia (absence of the iris), genitourinary malformations and neurodevelopmental delay.

In case of congenital adrenal hyperplasia the recurrence risk is 25%.

Ambiguous genitalia are often diagnosed postnatally during early neonatal assessment, although prenatal diagnosis arises when fetal sex cannot be determined at the second trimester anatomy scan. Rarely diagnosis can be made later during pregnancy. In case of a female fetus the usual finding is clitoromegaly with normal labia while in case of male fetuses the usual findings are micropenis, hypospadias, undescended testes or bifid scrotum.

On prenatal ultrasound, normal female genitalia in the midtrimester are characterized by two echogenic parallel lines in a transverse section representing the labia. A clitoris may be seen between these labia and should be directed caudally. The uterus occasionally can be seen in the second half of gestation as a mass between the bladder and rectum, but its absence is an unreliable indicator for sex determination. Normal male genitalia are characterized by the presence of a scrotum, which may not be seen prominently until the third trimester when testicular descent occurs. The phallus is usually seen pointing cranially. In this case bladder and rectum are proximal due to the absence of a uterus between them. Color Doppler can be used to see urine streaming from the tip of the penis. Nomograms for scrotal diameter, penile length and bilabial diameter have been published but rarely used.

Thus, ambiguous genitalia are noted when the aforementioned signs are mixed or not clearly identified. Specifically, ambiguous genitalia are often seen as a short phallus (or, conversely, clitoromegaly) with bifid scrotum (or, conversely, labial swelling). Generally, sonographic fetal sex determination should not be attempted before the second trimester. If ambiguous genitalia are suspected, imaging in the late second and early third trimesters can allow a more accurate assessment.

Conditions that could affect clear view of fetal sex are: bladder exstrophy, caudal regression syndrome, sacrococcygeal teratoma, several forms of epispadias.

Treatment of a neonate with ambiguous genitalia should be performed by a multidisciplinary team, including geneticists, pediatric endocrinologists and pediatric urologists. There is controversy concerning sex assignment and the need or not of reconstructive surgery.

Whenever ambiguous genitalia are seen a detailed ultrasound examination is indicated. Maternal signs of hyperandrogenism (acne, deep voice, development of hirsuitism during pregnancy) should be searched for and history of androgens ingestion during the first trimester should be asked for. Also, family history of ambiguous genitalia should be elicited. The genetic sex determination is crucial and can be easily done through invasive testing or cfDNA in maternal blood. In families at risk of congenital adrenal hyperplasia invasive testing for DNA analysis should be performed. In cases compatible with Smith–Lemli–Opitz syndrome amniocentesis should be offered to measure 7-dehydrocholesterol levels; high levels  suggest the diagnosis of the syndrome.

In families with congenital adrenal hyperplasia, dexamethasone administration to the pregnant woman from 6 weeks of gestation can minimize the effect of androgens on fetal genitalia and the developing brain. If the fetus is male, steroids should be discontinued. Follow-up scans every 4 weeks are used to monitor growth and evolution of fetal genitalia.

Obstetric care follows the standard protocol but delivery should be in a tertiary center.

Because of the complex genetic, hormonal, physical and social factors involved, determination of fetal sex in cases of ambiguous genitalia is best done postnatally, incorporating an array of clinical consultants.

There is no specific prevention for the condition other than avoiding steroids during pregnancy.

1. Chitayat, D. and Glanc, P. (2010), Diagnostic approach in prenatally detected genital abnormalities. Ultrasound Obstet Gynecol, 35: 637-646

2. van Bever Y, Groenenberg IAL, Knapen MFCM, Dessens AB, Hannema SE, Wolffenbuttel KP, Diderich KEM, Hoefsloot LH, Srebniak MI, Bruggenwirth HT. Prenatal ultrasound finding of atypical genitalia: Counseling, genetic testing and outcomes. Prenat Diagn. 2022 Jul 9.

3. https://fetalmedicine.org/education/fetal-abnormalities/genital-tract/ambiguous-genitalia

4. https://radiologykey.com/ambiguous-genitalia/

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