While going off on a tequila bender is decidedly not a good thing if you're carrying an unborn child, there's an increasing body of evidence that suggest low to moderate drinking might not be the worst thing imaginable for your baby. A cohort of five papers have just been published from Denmark, looking at maternal drinking and its effects on five-year old children — and for a drink every now or then, it seems to be fine.
The papers studied the effects of low (1-4 standard drinks per week), moderate (5-8), heavy (9+), and binge (5+ on a single occasion) levels of drinking, and how the children were five years down the line. (It's worth noting that this is based on the Danish standard drink, which is 12 grams of pure alcohol — higher than the UK's 7.9 grams, lower than the USA's 14 grams, and far, far below Japan's 19.75 grams. I guess a standard drink isn't really standard.)
The papers looked at the IQ, attention span, and executive functions such as planning, organisation, and self-control in five-year-old children whose mothers had drunk during the early days of pregnancy, and compared them to a dry control group. Surprisingly, the harm to the children was remarkably minor. Amongst the fewer than eight drinks a week cohort, there was no significant effect on neurodevelopment of children at the age of five. Even more bizarrely, the same was true for those that had had a binge drinking event.
However, repeated high use of drinking did have an effect — those children with mothers who had an intake of 9+ drinks per week had a lower attention span than other five year olds, and were at an increased risk of lower IQ. This isn't an excuse to go out and drink a beer tower while pregnant — in fact, the doctors behind the studies still recommend that expecting mothers be very careful.