Testicles that move are normal

The commonest version of this worry is not undescended testicles at all. The American Academy of Pediatrics describes what a newborn scrotum does: "The scrotum of a baby boy may be small and smooth, or it might be large and wrinkled. The testicles can appear to move in and out of the scrotum, and sometimes will move as far up as the base of the penis or even to the crease between the thigh and belly."

And the rule that follows: "As long as the testicles are located in the scrotum most of the time, the fact that they move around is normal."

A cold room, a nappy change or a startle can pull a testicle up out of sight for a while. Checking in a warm bath, when your baby is relaxed, gives a much more useful answer than checking on a cold changing mat.

Undescended testicles

The NHS defines it: "Undescended testicles are where the testicles are not in the usual place in the scrotum. It's common in young boys, and the testicles often move to where they should be on their own, but sometimes surgery is needed."

The cause is developmental rather than anything that happened at birth. The NHS: "When a baby boy is developing inside the womb, their testicles grow inside their tummy and later move down into the scrotum before they're born. But sometimes the testicles do not move into the usual place."

Risk is higher if your baby was born prematurely, before 37 weeks, had a low birth weight, or has relatives who had undescended testicles. Prematurity is the biggest single factor, because descent happens late in pregnancy.

Who checks, and when

The NHS says undescended testicles "are usually found when your child has their newborn physical examination", which happens in the first few days after birth. NICE's postnatal care guideline NG194 specifies that this examination includes "genitalia and anus: completeness and patency and undescended testes in boys", and that the complete examination is repeated at six to eight weeks.

The NHS also notes that during the first weeks "your child's testicles will usually be checked at their regular health visitor appointments" — the health and development reviews — so this is followed up rather than checked once.

The timetable

This is the part worth writing down, because it is specific and because it tells you when to chase.

First 12 weeks: the NHS says undescended testicles "often move into their usual place in the scrotum in the first 12 weeks after your child is born". Watchful waiting during this period is the plan, not a delay.
Both testicles affected: referral to a specialist may happen sooner, "usually after 8 weeks".
One testicle affected: if it has not moved into the scrotum within 4 to 5 months, your child will usually be referred to a specialist.
Surgery: an operation to bring the testicle down, called orchidopexy, "will usually be done when your child is around 1 year old". The NHS says it is safe and effective.

The NHS adds the reason not to leave it: "If undescended testicles are not treated, they can cause your child health problems." Timing matters, which is why the referral windows are as tight as they are.

Swelling, and the one that is urgent

Newborn genitals often look swollen and red, and the AAP notes they "can be reddish and seem large for bodies so small". Two specific things sit behind that.

Hydrocele. The AAP: "Some boys have a buildup of fluid in a sac called a hydrocele inside the scrotum. This buildup will shrink gradually without treatment over several months as the fluid is reabsorbed by the body." A hydrocele is soft, painless and often on one side, and it needs nothing done.

Inguinal hernia. The AAP gives the exception clearly: "If the scrotum swells suddenly or gets larger when he cries, notify your pediatrician; this could be a sign of an inguinal hernia, which requires treatment." A hernia that becomes stuck is a surgical emergency. Sudden swelling, a firm lump in the groin, a scrotum that is red, hard or tender, or a baby who is vomiting and distressed alongside groin swelling all need to be seen immediately rather than the same day.

How to check at home

Do it warm. In the bath, or shortly after, when your baby is relaxed.
Use warm hands and a light touch. Cold hands trigger exactly the reflex you are trying to avoid.
Feel gently for two small round glands in the scrotum. The NHS describes the main symptom as "not being able to feel 2 round glands (testicles) inside your child's scrotum".
Do not squeeze or manipulate, and do not try to bring a testicle down yourself.
Note what you find over several days. A testicle that is there sometimes is a different finding from one that is never there, and clinicians will ask.

When to call

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand), or go straight to an emergency department, if your baby:

Has a scrotum or groin that swells suddenly, or a lump that has become firm, red or tender.
Is vomiting, inconsolable or looks unwell alongside groin swelling.
Has a temperature of 38C (100.4F) or above, or below 36C (96.8F).
Looks pale, ashen, mottled or blue, or is unresponsive or unrousable.
Has a weak, abnormally high-pitched or continuous cry.
Is grunting, breathing over 60 breaths a minute, or has a bulging fontanelle, a seizure, or a rash that does not fade under a pressed glass.

Those last items are NICE's red flags for serious illness in young babies, from NG194.

Speak to your health visitor, public health nurse or GP if: you cannot feel one or both testicles; a testicle was there before and now is not; both testicles are undescended and your baby is approaching eight weeks with no referral; one testicle is still not down at four to five months; or you notice any change in your child's testicles that is not usual. The NHS's own trigger for seeing a GP is exactly that broad.

What to let go of

A testicle that plays hide and seek is normal, and the AAP says so explicitly. What is worth tracking is whether they are in the scrotum most of the time, and whether the timetable above is being followed. This is one of the few newborn findings where the calendar genuinely matters, so if you reach the twelve-week or four-month marks without a plan, ask for one.

Undescended Testicles in a Newborn