No, doctors are making blood test or ultrasound during pregnancy, around 10-12th week of pregnancy. And when kid is born they are only checking by genitals if everything correct.

To check if it is male or female for sure, they will need to do X-rays and blood test of a newborn. That's pretty invasive and does not worth it to do, because it will take a lot of resources and can hurt mother or kid, especially when speaking about such rare condition

Violet, whilst I agree with your points overall, for the sake of others who will read this thread, I want to point out that screenings for the presence or absence of internal organs like undescended testes, ovaries, uterus, etc doesn't require X-rays; scanning by ultrasound works fine and is the customary method - and it's not invasive, nor does it cause any health risks like X-rays do.

Moreover, and more to the point, in many places in the world, mandatory blood tests on newborns are already done to check them for a variety of genetic disorders.

In the US, for example, each of the 50 states (as well as in the District of Columbia and I believe in the territories) have laws in place that make it mandatory by law for blood to be drawn from newborns' foot shortly after birth so it can be determined if the child has various very rare genetic disorders. Exactly which disorders are tested for varies a bit depending on the jurisdiction.

Here is the list of the disorders newborns are currently tested for by law in New York state. https://www.wadsworth.org/programs/newborn/screening/screened-disorders

As you can see, it includes testing for one DSD, namely the specific type of Congenital Adrenal Hyperplasia caused by

CAH1, CYP21 deficiency, Hyperandrogenism, nonclassic type, due to 21-hydroxylase deficiency

Congenital adrenal hyperplasia (CAH) is a group of inherited endocrine disorders of impaired steroid hormone production by the adrenal glands. The synthesis of cortisol in the adrenal gland requires the production of a number of different enzymes, the lack of which will result in CAH. In 95% of CAH cases, 21-hydroxylase deficiency causes CAH and therefore newborn screening tests for the deficiency in this enzyme. In 21-hydroxylase deficiency CAH, the adrenal glands produce too much male sex hormone (androgens) which cause many of the symptoms of CAH. Additionally, in severe forms of CAH, the resultant lack of cortisol and aldosterone can cause life threatening complications. Cortisol is important for the body’s stress response and for controlling blood sugar levels. Aldosterone is important for regulating sodium balance in the body.

Below is the listing of the genetic disorders newborns in the state of Connecticut, which is next door to NY, are tested for, as well as a list that groups the disorders together by type. It includes CAH too, though Connecticut's website doesn't go into the same detail as the NY website does:

https://portal.ct.gov/-/media/DPH/NBS-Forms-and-Documents/Conditions_alphabetical_by_disease_01-2020.pdf

https://portal.ct.gov/-/media/DPH/NBS-Forms-and-Documents/Conditions_by_classification_01-2020.pdf

All the genetic conditions that the various states in the US do mandatory testing of newborns for are conditions in which early diagnosis and intervention is necessary to guarantee the child's survival in infancy or to stave off severe, irreversible damage to his or her physical health that can lead to disability and early death down the line. Such as cystic fibrosis, sickle cell and severe combined immune deficiency or SCID (aka "bubble boy disease").

However, even where such conditions are sex-linked, as in the case of SCID, testing to determine a child's sex chromosomes is not part of mandatory newborn blood screening protocols in any jurisdiction in the US.

From the viewpoint of practicality, in the US (and many other countries today) testing all newborns' blood for genetic anomalies known to cause various DSDs is possible and affordable - just as testing for any of thousands of other genetic anomalies that cause or can cause a host of other medical conditions is today. However, testing for all these other conditions is not done because of costs and many ethical issues. In order to justify adding CAIS - or any other DSD - to the mandatory newborn screening done in the USA today, it would have to be known exactly what genetic anomaly/ies cause it - and it would have to shown that unless diagnosed at birth, the condition can or will lead to death, will greatly reduce the child's expected life span, or is sure to cause severe physical health problems that can't be addressed and ameliorated if the condition is diagnosed at a later date in life.

CAIS does not fit this criteria. Nor, AFAIK, do other DSDs except for the salt-wasting form of CAH that u/ColoredTwice has and which US newborn screening programs already include as a matter of course. That's the one DSD that can be fatal if not diagnosed and treated early. As you noted, most DSDs do not require any medical intervention in childhood. And the possible presence of any DSD where early intervention might be something recommended or considered would be indicated by the appearance of the child's genitals and thus lead to further medical investigation and diagnosis.