Men trying for a baby can cause birth defects by boozing just once a week by more than a third, according to new research.

Infants of fathers who drank are most prone to cleft lips and palates – with cases soaring by 55 percent.

It adds to increasing evidence a man’s lifestyle can harm a child in the womb – as well as a woman’s.

Corresponding author Professor Xiaotian Li, a gynecologist at Fudan University, Shanghai, said:

“Our finding suggests future fathers should be encouraged to modify their alcohol intake before conceiving to reduce foetal risk.”

It was based on over a million parents in China where one in three of the dads drank before pregnancy – and only three percent of the mums.

The rate of birth defects was 35 percent higher among couples who reported ‘paternal drinking’ – with clefts rising “especially”, said Prof Li.

It occurs when separate parts of the face do not fuse correctly during foetal development.

They affect more than 1,000 new-borns in the UK each year – making them the most common abnormality.

It is believed to be due to a combination of genetic and environmental factors.

Previous studies have shown alcohol reduces men’s testosterone levels – and damages sperm.

But the affect on future sons and daughters has been difficult to measure.

Up to three in ten women in Western countries drink before and during pregnancy which skews results.

The analysis in JAMA Pediatrics focused on a unique population of mainly male drinkers – making it the first of its kind.

Couples planning a pregnancy within six months provided precise information on paternal alcohol consumption.

This was defined as at least one drink a week. Birth defects were reported six weeks after delivery.

Calculations took into account a multitude of potential contributory factors.

They included medical history, exposure to harmful substances, maternal age and drinking and paternal smoking.

It’s well-known alcohol can cause problems for a developing baby throughout pregnancy – such as disfigurements.

Prof Li said:

“It’s widely recommended for women to quit consuming alcohol before and during pregnancy.”

But the safety of fathers drinking before conception has barely been considered,

He said:

“Paternal alcohol exposure biologically increases the risk of sperm abnormalities.”

Epidemiological data is scarce due to maternal issues muddying the waters. The rare drinking of mothers in China got round this.

Prof Li said:

“This study aimed to investigate the association between paternal drinking before pregnancy and birth defects to provide supportive evidence for alcohol cessation in preconception health care.

“It provides evidence for clinical recommendation and public health strategy making to improve offspring life quality.”

An earlier study of 340,000 births by another Chinese team found those whose dads drank around the time of conception were 44 per cent more prone to heart disease.

They advised men not to imbibe for six months before trying for a baby. If mums enjoyed a tipple before getting pregnant, the risk rose 16 percent.

British experts say would-be parents do not need to ditch all boozing – but advise sensible drinking.

Four years ago a major study named Britain seventh out of 195 countries for the proportion of children with ‘foetal alcohol spectrum disorder‘.

Also known as FASD, it’s a series of developmental problems caused by exposure to booze in the womb.

The Canadian team found about 32 in every 1,000 Britons have FASD – compared to the global average of eight in 1,000.