Is a single glass of wine safe in pregnancy?

I came across this blog post which is very interesting on the most harmful time to drink during pregnancy.
Interestingly, this study found that it is those first few weeks after the first trimester. This really surprised me!

http://pregnancy-blog.parentingweekly.com/2012/01/end-of-first-trimester-is-worst-time-to.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+parentingweekly%2FujFj+%28Pregnancy+Blog+-+For+All+Your+Pregnancy+Things+by+PregnancyWeekly%29

Most pregnant women I know are abstaining from alcohol most of the time bit will allow themselves the odd glass of wine here or there. I decided on a maximum of one glass a week, although I don't have one every week - more recently I just forget. If I don't fancy one then I won't bother. However, it was back after the 12 week scan when we had the 'all clear' that I did have the odd glass once a week. I was still really missing wine and hadn't yet changed my lifestyle to match my condition.

The fact that this 13-14 week window was actually the most critical time is really concerning. On a positive note, the sample size is only 900 women and it sounds like the women drank a lot more then one glass a week. It does make you wonder though...