Birthdays determine babies' height

The study showed a link between height and the month of birth

A baby's height can depend on the month of birth, with the tallest babies being born in the spring and autumn and the shortest entering the world in December.

The finding comes in a study published in The Lancet medical journal, and supports an earlier study linking the month of birth to height.

The study involved 1,166,206 children born in Denmark between 1973 and 1994. The country's National Birth Registry holds records on how long babies spent in the womb and their height and weight at birth.

It showed that babies born in April were on average 2.2mm taller than those born in December.

Those born in midsummer were also shorter than spring and autumn babies.

Earlier findings

Dr Jan Wohlfahrt and colleagues from the Danish Epidemiology Science Centre in Copenhagen conducted the research.

It supports a study published earlier this year by scientists in Austria that found a height variation of up to 6mm in 18-year-old men depending on their month of birth.

However, that study only found increased height among those born in the spring.

There is no clear explanation for the discrepancies, although the scientists have put forward some theories.

The team found that the pregnancies that resulted in December, January and February births were on average one day shorter than for children born in other months.

They also suggested that it was possible that a seasonal intake of inexperienced midwives could lead to inaccurate measurements of baby length.

However, they said this was unlikely as they also found seasonal variations in weight at birth, which is much easier to measure accurately.

Environmental factors

Dr Wohlfahrt's team said that the discrepancies must be connected to environmental factors both before and immediately after birth.

The scientists said: "The variations in length at birth were partly consistent with the variations reported for men aged 18 years.

"The seasonal pattern at birth was similar across strata of birth year, sex and gestational age, which supports the hypothesis that month of birth is important for adult stature.

"Similar studies in the southern hemisphere are needed," they added.

Tam Fry, chairman of the Child Growth Foundation, said: "We know, and have known for some time, that there is a seasonal variation in growth, but it is quite a surprise that there is this marked difference in foetal growth.

"The interesting thing is that the foetus would not know the difference between winter and summer and the mother would have ceased to be influenced in her growth pattern unless they were very young mothers."