London - Most parents have no idea whether their little one will arrive with a thick thatch or bald as a coot, blonde or brunette.
But their own hair can be a good indicator of what to expect.
"We have many genes from both parents and beyond which may influence hair type, abundance, colour and density," says trichologist Iain Sallis.
Dr Anand Saggar, a consultant in clinical genetics, adds: "You have not just got the parents’ own type of hair, but also the additional influence of the combination of those two genomes coming together."
Babies with thick hair are more common in parents of Mediterranean and Asian heritage. But the darker pigmentation can also make hair appear fuller, even if the baby has the same number of strands as another child with lighter coloured hair.
"You have more hair follicles if you are blonde," says Harley Street trichologist Sara G Allison, of hairlossconsultant.co.uk.
"But the hair may be finer than dark hair. Blonde hair reflects the light, creating an optical illusion that dark hair looks more abundant."
Hair growth in babies starts long before birth. A foetus grows a type of soft hair called lanugo from around four to five months old, which spreads around the whole body. It is believed to help regulate the unborn baby’s body temperature, and forms a barrier to the vernix = the thick, white substance that sometimes still coats a baby at birth - which is there to protect the unborn child’s skin from the amniotic fluid.
Some premature babies are born still covered in this downy hair. But usually lanugo is shed between the seventh and eighth month of pregnancy and replaced by vellus hair, which is finer.
According to urban myths, how much hair a newborn will have can be predicted from what the mother eats during pregnancy and whether she has experienced heartburn.
While there is no proof of the former assertion, there is some for the latter.
In 2007, US researchers conducted a study of 64 pregnant women, about 78 percent of whom had reported experiencing heartburn. After they gave birth, of the 28 who had reported moderate to severe heartburn, 23 had babies with average or above-average amounts of hair, while those who had reported no heartburn had babies with little or no hair.
This may be attributed to the hormone oestrogen, which in high levels can cause heartburn and influence foetal hair growth.
And while baby hair is often a source of parental pride - it may not last. Hormonal changes can prompt a baby to enter a hair loss - telogen - phase at the same time as its mother, at around eight to 12 weeks, before it grows back again.
And what grows back can be quite different to the first head of hair - potentially changing in colour and texture.