Western Europe is beginning to cede some ground to central and eastern Europe, in terms of growth, according to our latest Global Monitor report. While there are still relatively unsaturated western markets like Germany and Spain making headway, others like the United Kingdom and Iceland have slowed or stopped growing this month. Meanwhile, Poland and Romania, among others, are quickly adding Facebook users.

As a whole, Europe is now up to 129 million users as of March 1st, a 5.1% increase from February. That’s slightly slower growth than during the previous month, but there’s no reason to think that the region as a whole is slowing down, as total penetration is only up a single point to 20 percent.

The top grower over the past month was Germany, followed by Italy. Last month it was Turkey, whose internet population is both geographically and culturally related to the European continent.

As to why Turkey’s growth is slowing, the easy answer is that its market penetration is fairly high. Out of the ten countries listed above, it is at the top in terms of penetration, at 27.5 percent. Big markets tend to top out somewhere between 35 and 40 percent.

In coming months, expect Germany to continue appearing as a top grower; its penetration is still just under 10 percent, but Facebook appears to have gotten a good foothold against native social networks like StudiVZ. Germany’s strong 15 percent growth rate has held steady for two months now.

What you’re not seeing here: a great many of Europe’s smaller countries, by number of internet users, that are nevertheless rapidly sending people Facebook’s way. That includes Hungary, which almost made it into the top ten above, as well as Estonia and Ukraine. We cover growth, penetration and more stats for almost 100 countries in our full monthly Global Monitor report.