dor yesharim testing for a married couple

Shalom,
There is room for genetic testing even after marriage. The fact that the couple has a number of healthy children is not sufficient indication that there are no serious genetic concerns, since the statistics are often only 1 in 4.
The primary consideration of whether to test revolves around the response of the couple to the results. It is important that they properly understand the results of the genetic testing, and the statistics and implications that accompany each result.
Sometimes the statistics are of real concern. Nowadays, it is often possible to have subsequent children through PGD, a form of IVF in which the embryos are screened for the relevant genetic condition, and only fetuses that do not carry the relevant gene are implanted. (See www.medethics.org.il/db/showQ.asp?ID=6078)
Sometimes, though, the statistics are of minimal concern, but the couple comes under great stress knowing that they are "carriers" of specific genes, which can lead to a desire not to have additional children or to even to divorce. It also raises questions of disclosure when their children approach age of shidduch. Other couples are able to deal with the results in a more measured manner. 
As an informal recommendation, if the couple has not participated in Dor Yesharim testing, it is worthwhile to test afterwards, since the potential gains outweigh the possible emotional stress. If the couple has already participated in Dor Yesharim, they can still do additional tests if they feel equipped to handle the results.
Kol Tuv,
Meir Orlian