Irish married couples are 30 percent more likely to split up after having their first baby, a new survey has found.

The survey results  were described by Pete Lunn one of the authors as "quite surprising . . . Our favored explanation is that a first child can put strain on the relationship, while having more children is a sign that any strains were overcome."

The survey, conducted by the Economic and Social Research Institute and University College Dublin, also showed a strong swing towards couples living together but not getting married. Those aged 25 and under were twice as likely to be living together.

Researchers also found that  "delayed fertility has become the norm” with most woman waiting until they are in their 30s to have children. The more educated the woman, the more likely she is to wait until later in life to have kids the survey showed.

Most women now have two to three children but one in six women have no children at 45.

Overall, the number of Gay couples living together remains small, (0.15 percent of 15-59-year-olds) but it is on the rise  from 150 in 1996 to 2,090 in 2006.

Most gay couples are in their 30s and 40s, have high educational achievement and are living  in Dublin.

The study showed that marriage break up peaked in the 90s but has leveled off since

"There is no evidence that the introduction of divorce in 1997 affected the trend in marital breakdown," the report said.