The birth of a first and a second child briefly increases the level of their parents' happiness, but a third does not, according to new research from the London School of Economics and Political Science (LSE) and Western University, Canada.

According to the research, published in the journal Demography, parents' happiness increases in the year before and after the birth of a first child, it then quickly decreases and returns to their 'pre-child' level of happiness.

The pattern for second births is similar, although the increase in happiness before and around the birth is roughly half of that for first births. The increase in parental happiness surrounding the birth of a third child is negligible.

Mikko Myrskylä, professor of demography at LSE and Director of the Max Planck Institute for Demographic Research in Rostock, Germany, said: "Our results show a temporary and transitory gain in parents' happiness around the birth of first and second children.

"The fact that parental happiness increases before these children are born suggests that we are capturing broader issues relating to childbearing such as couples forming partnerships and making plans for the future.

"The arrival of a third child is not associated with an increase in the parents' happiness, but this is not to suggest they are any less loved than their older siblings. Instead, this may reflect that the experience of parenthood is less novel and exciting by the time the third child is born or that a larger family puts extra pressure on the parents' resources. Also, the likelihood of a pregnancy being unplanned may increase with the number of children a woman already has -- and this brings its own stresses."

Compared to men, women gain more in happiness in expectation of, and right after, the birth of a child. Women also have steeper drops in their happiness than men between the year of the birth and the year afterward, possibly because of the larger initial gain. However, in the long run, there are no differences between the happiness levels of men and women before and after children.

Those who have children at an older age or who are more educated have a particularly positive response to a first birth. Older parents, between the ages of 35 -- 49, have the strongest happiness gains around the time of birth and stay at a higher level of happiness after becoming parents.

Those who become parents in their teens have a predominantly declining pattern of happiness that does not increase above the baseline even during the year of birth. Those who become parents between the ages of 23 -34 have increasing happiness before a first birth, however one to two years after the birth, happiness decreases to baseline or below.

Rachel Margolis, assistant professor from Western University's Faculty of Social Science, said: "The fact that among older and better-educated parents, well-being increases with childbearing, but the young and less-educated parents have flat or even downward happiness trajectories, may explain why postponing fertility has become so common."