Androgen insensitivity syndrome (AIS) is sometimes diagnosed soon after a baby is born, although often it's not noticed until a child reaches puberty.

Doctors may suspect AIS based on a child's appearance and sex development, but some tests will be needed to confirm their diagnosis.

Partial androgen insensitivity syndrome (PAIS) is usually spotted soon after birth because the genitals have an unusual appearance.

Complete androgen insensitivity syndrome (CAIS) is not usually diagnosed at birth because the genitals look normal for a girl. But CAIS may be picked up if the child gets a hernia.

A hernia is where an internal part of the body pushes through a weakness in the surrounding tissue. Babies with CAIS can get a hernia if the testicles fail to move from the tummy into the scrotum.

When the baby has an operation to repair the hernia, the surgeon may find the testicles inside the hernia or tummy. Tests may be arranged to check for CAIS.

If a baby with CAIS does not develop a hernia, the condition may go undiagnosed until puberty, when she does not start having periods and does not develop pubic and underarm hair.

Read more about the symptoms of AIS.

If AIS is suspected, blood tests can be used to:

• check the sex chromosomes – sex chromosomes are bundles of genetic material that determine a person's genetic sex; if their genetic sex is different from their physical appearance, they may have AIS
• check for a genetic change – AIS is caused by an alteration on the X chromosome, the sex chromosome a child with AIS receives from their mother
• measure sex hormone levels – children with AIS tend to have high levels of testosterone (the male sex hormone) in their blood

An ultrasound scan can also be used to confirm the absence of the womb and ovaries. Children with AIS often have female external genitals, but no female internal reproductive organs.

If a surgeon thinks they've found testicles in a baby's tummy during a hernia repair operation, a small tissue sample (biopsy) may be taken and analysed to confirm they are testicles and not ovaries.

If someone in your family has AIS and the specific gene causing it has been identified, it may be possible to have a blood test to check if you carry the same gene and are at risk of passing it on to any children you have.

Testing can also be carried out in unborn babies when there's a known family history of AIS.

There are 2 main tests that can be carried out during pregnancy to determine whether a baby has AIS:

• chorionic villus sampling (CVS) – a sample of cells is removed from the placenta for testing, usually with a needle; this is usually carried out between week 11 and week 14 of pregnancy
• amniocentesis – a needle is used to extract a sample of the fluid surrounding the baby (amniotic fluid) for testing; this is usually carried out between week 15 and week 20 of pregnancy

It can be difficult to decide whether or not to have these tests, which do carry a risk of miscarriage, so it's a good idea to speak to a genetic counsellor first.