Women who drink as little as one small glass of wine a week while pregnant could risk reducing their child's IQ, a study has suggested.
The effect is only felt by children who have genes that make them vulnerable to alcohol, scientists found.
For these children, even being exposed to relatively small amounts of alcohol before birth could have a significant impact on intelligence at age eight.
It is already well known that heavy drinking in pregnancy can severely harm an unborn baby.
But the picture is less clear with regard to light or moderate alcohol consumption.
Some guidelines urge mothers-to-be to avoid alcohol completely, while others suggest a moderate intake is safe.
The new findings, published online in the journal Public Library of Science ONE, suggest that genes have a strong bearing on the effect of alcohol in the womb.
Scientists studied four genetic variants in more than 4,000 children that influence the body's ability to metabolise, or break down, alcohol.
They also questioned mothers about their drinking habits while they were pregnant.
Test results showed a lowering of IQ for genetically susceptible children whose mothers consumed between one and six units of alcohol per week.
Read our tips for encouraging a health pregnancy
A unit of alcohol is roughly equivalent to one small glass of wine, a pint of beer, or a single measure of spirits.
At eight-years-old, IQ was reduced by almost two points on average for each of the genetic variants a child possessed - but only if his or her mother drank while pregnant.
Children whose mothers avoided alcohol completely were not affected, even if they had alcohol-sensitising genes.
Lead researcher Dr Ron Gray, from Oxford University, said: "This is a complex study but the message is simple: even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence.
"So women have a good reason to choose to avoid alcohol when pregnant."
Colleague Dr Sarah Lewis, from the University of Bristol, said the research showed that levels of alcohol that are normally considered harmless can have an impact on childhood IQ.
"This is evidence that even at these moderate levels, alcohol is influencing foetal brain development," she added.
Superfoods For Pregnancy
<strong>Benefit To Baby:</strong> Healthy Growth Protein is needed to build and repair cells, and is essential to a baby's development and growth. Red meat and dairy are rich in protein, but they're also high in saturated fats. Balance your diet with fish protein (in all fish products), which also contains essential fatty acids. And don't forget vegetable protein, which includes brown rice, quinoa, chickpeas, lentils, baked beans, pumpkin seeds and cashew nuts. A great alternative protein source, tofu is low in fat and will help balance those blood sugar levels. Add to juice from pomegranate and mixed berries for a sweet drink that also packs a powerful antioxidant punch.
<strong>Benefit For Mother And Baby:</strong> Boost Energy Levels And Provides Nutrition To Baby Iron is vital for your baby's physical growth and brain development, and helps produce the blood required to supply nutrition to the placenta. Not enough iron, and you can feel tired and be more susceptible to infections. There's also a greater risk of premature birth and your baby having a low birth weight.
<strong>Benefit To Baby:</strong> Brain Development Vitamin B6, also known as pyridoxine, helps your body metabolise protein, fats, and carbohydrates. It also helps form new red blood cells, antibodies, and neurotransmitters, and is vital to your baby's developing brain and nervous system.
<strong>Benefit To Mother:</strong> Helps Constipation Many pregnant women suffer from constipation, which is cause by an influx of hormonal changes that play havoc with the digestive system. It To avoid discomfort and to help regulate your bowels, eating a <a href="http://www.huffingtonpost.co.uk/2011/12/29/banish-that-post-christmas-bloat-high-fibre-foods_n_1174063.html#s578333&title=Spinach" target="_hplink">rich fibre diet</a> will help get things moving, as they help absorb excess acid and gas, help to speed up digestion and empty your stomach faster. Foods like brown rice, dried figs, kidney beans and avocado are all rich sources of fibre. Pumpkins are great as they offer fibre plus it's said to act like a mild laxative.
Yoghurt And Honey
<strong>Benefit To Mother And Baby:</strong> Increases Energy Levels And Bone Building High in calcium (important during pregnancy for building your baby's bones) with a sweet kick from the honey, this treat should tide you over without making you sleepy. Dairy foods provide vitamins A and D, which are essential for bone-building and bone maintenance for you and your baby. They are also a good source of protein.
<strong>Benefit to Mother:</strong> Eases Heartburn And Water Retention Dried figs are laden with digestive enzymes, which should help you to digest your food and ease those heartburn symptoms. They're also rich in the essential mineral potassium, which helps to maintain the body's fluid balance during pregnancy, which is essential to battling swollen legs, hands and ankles.
<strong>Benefit To Baby:</strong> Maintains Healthy Nervous System Omega-3 fatty acids are vital for your baby's brain and nervous system, as well as your own mental health. Foods rich in omega-3 include oily fish like fresh tuna, mackerel and sardines, although restrict your intake to twice a week, as too much fish can increase risk of pollutants. Fatty acids help brain development and work to improve its function, so as well as being nutritious, slow-releasing energy snacks, like sesame seeds, which help keep you mentally alert and working well throughout the day.
<strong>Benefit To Mother:</strong> Alleviates Morning Sickness Ginger has long been associated with alleviating nausea and has been used as a medicine in Asian, Indian, and Arabic herbal traditions since ancient times. In China, for example, ginger has been used to help digestion and treat stomach upset, diarrhea, and nausea for more than 2,000 years. Ginger biscuits are a good food to nibble on when the nausea starts, or sip on ginger tea or suck on ginger flavoured sweets. Peppermint and mint are also great nausea-relieving agents too.
<strong>Benefit To Baby:</strong> Strengthens Bones Sweet potatoes offer a rich source of folic acid, which helps prevent neural tube defects in foetuses. It also protects your unborn baby from spinal cord problems, such as spina bifida. lentils are also a great for increasing your folic acid intake, as one cup provides 358mcg of folic acid, almost the daily requirement of 400mcg. Fruits like strawberries are a great way to get your folic acid, and even tastier if you dip them in chocolate! Scientists in Finland found that eating chocolate when pregnant resulted in happier, livelier babies, but keep your waistline in mind and be conservative when dipping.
Almonds And Apricots
<strong>Benefit To Mother:</strong> Curbs Food Cravings A handful of almonds and apricots will provide you with a sweet kick that's high in protein - this will help to curb cravings as well as keeping you feeling fuller for longer.
<strong>Benefit To Mother:</strong> Protects From Pre-eclampsia Parsnips are a good source of fibre and folate (the natural form of folic acid), as well as providing potassium (associated with a lowering in blood pressure) which is vital for protecting against pre-eclampsia, a condition caused by high blood pressure.
Alcohol passes easily from a mother's bloodstream to her baby via the placenta.
When ethanol alcohol enters the body, certain enzymes convert it to acetaldehyde.
Variations in genes that code for these enzymes mean that some individuals metabolise alcohol more efficiently than others.
In slow metabolisers, peak alcohol levels persist in the body for longer.
No unborn baby, whatever kind of genes it possesses, has an adult's ability to metabolise alcohol.
Dietician Catherine Collins, from St George's Hospital NHS Trust in London, said alcohol was likely to stay longer in the bodies of unborn babies with the susceptibility genes and do more damage.
She added: "What do mums take from this?
"Unfortunately it's a bit of a gene lottery.
"If your child has a particular gene profile, drinking any alcohol in pregnancy will have an effect on IQ - but, and it's a big but - your child may not have one of those identified gene defects, and so the effect is negligible."
Dr Simon Newell, from the Royal College of Paediatrics and Child Health, said: "We already know that an estimated 6,000 babies a year in the UK are born with brain damage, physical problems or learning disabilities as a result of heavy alcohol consumption by their mothers while pregnant.
"It is impossible to say what constitutes a 'safe' amount of alcohol a mother can drink as every pregnancy is different, so our advice to mothers is don't take the chance with your baby's health - drink no alcohol at all."
The research forms part of the Avon Longitudinal Study of Parents and Children (Alspac), which enrolled more than 14,000 pregnant women in 1991 and 1992.
Alspac scientists have been closely scrutinising the health and development of the women and their children since the start of the investigation.
They are currently recruiting the next generation into the study.