Guttmacher Institute Reasons

In more or less routine publication of Guttmacher Institute, Legal Abortion Worldwide in 2008: Levels and Recent Trends by Gilda Sedgh, Susheela Singh, Stanley K. Henshaw and Akinrinola Bankole published by International Perspectives on Sexual and Reproductive Health, 2011, 37(2):84–94, doi: 10.1363/3708411 (link to pdf) I have found interesting reduction of Russian rating of completeness of legal abortions reporting:

For some countries, the classification of the completeness of their statistics has changed since 2003. Abortion statistics for Belarus, Canada, Cuba, Latvia, Lithuania, Russia and Tunisia were deemed complete in 2003 but incomplete in 2008.

Since now the reporting is incomplete or completeness is uncertain. This statement is based upon another statement:

The proportion of abortions in Russia that are privately performed and unreported is increasing, according to experts and published research.¹¹ 

ref 11 is Philipov D et al., Induced abortion in Russia: recent trends and underreporting in surveys, European Journal of Population, 2004, 20(2): 95–117 (link to jstore). 
(et al = E. Andreev, T. Kharkova, and V. Shkolnikov)

 + more (of Guttmacher): 

However, experts indicated that the number of unreported, privately performed abortions in this region has increased substantially, though the levels of such abortions are unknown. Informants believed that the declines in the official numbers represent a combination of real declines in incidence and a shift to unreported abortions.

Experts and informants are not indicated ;(
However known authors (D. Philipov, E. Andreev, T. Kharkova, and V. Shkolnikov) in cited paper wrote:

... finding suggests that provider statistics on abortion in Russia are a true reflection of the situation they monitor, that the observed declining trend in abortion is a real one...

They tested the idea of statistics deterioration was a couse of abortion reduction.

It seems that Guttmacher Institute authors understood their reference exactly opposite ;)