In the study, more than 70% of parents reported a decline in happiness following the birth of their first child.
Rachel Margolis, of the University of Western Ontario in Canada, and Mikko Myrskylä, of the Max Planck Institute for Demographic Research in Germany, publish their findings in the journal Demography.
The purpose of the study was to gain a better understanding as to why some parents stop at having one child.
According to the most recent data from the US Census Bureau, the number of one-child families in the US has increased significantly in recent years. Today, more than 15 million American families with children only have one child.
The researchers note that there are a number of important social and demographic factors that may play a role in parents' decision to have more than one child. Past studies have shown that women are increasingly more career-driven, for example, meaning many are more focused on work than having children.
But Margolis and Myrskylä say no quantitative studies have investigated how the experience of having a first child impacts the desire to have more.
"The experience of the transition to parenthood will inform new parents' decisions about whether to have another child," they explain. "If having a first child is an overall positive experience, or more positive than anticipated, then people should be more likely to have another. However, if the transition to parenthood is very difficult or more difficult than expected, then people may choose to remain at parity one."
To investigate their theory, the team assessed 1984-2010 data of 2,301 German parents who were part of the German Socio-Economic Panel Study.
Each year of the study, both mothers and fathers were required to complete a questionnaire in which they rated their happiness on a scale of 0-10, with 10 representing maximum wellbeing. In addition, parents were asked about other life factors, including childbirth, relationships and employment.
The researchers used the information to assess participants' happiness 2 years prior to the birth of their first child and their happiness during transition to parenthood - up to 1 year after birth.
Over 70% of parents became unhappier after having their first child
They found that during the transition to parenthood, parents reported an average 1.4-point drop on the happiness scale, compared with 2 years before their first child was born.
Overall, more than 70% of parents experienced a decline in wellbeing after the birth of their first child, with over a third experiencing a minimum 2-point drop on the happiness scale.
In addition, the researchers found that parents who experienced a decline in wellbeing after their first child were less likely to have more children; 58% of parents who became unhappier went on to have a second child within 10 years, compared with 66% of parents whose happiness did not decline.
Parents aged 30 and older and those who stayed in education for at least 12 years were most likely to be influenced by their levels of happiness when it came to deciding whether to have more children, according to the results.
Myrskylä says this may be because older parents and those with better education are better at applying their recent experiences to fertility decisions. "It could also be that it is harder for these parents to combine work and family, given that they are likely to be in more competitive professional environments," he adds.
The researchers say their findings remained even after accounting for potential confounding factors, such as parents' income, marital status and place of birth.
Commenting on the importance of these findings, Margolis says:
"We now know that the drop in happiness is important, if not imperative, for determining whether couples go on to have another child. The happiness drop that occurs during the transition to parenthood is quantitatively important and holds far more weight than other major changes in the relationship, work, and health of a couple when determining the choice to have more children."
The study is subject to some limitations. For example, the researchers note that they were unable to determine the underlying mechanisms that lead to parents' difficulties during transition to parenthood.
"These factors, such as the ease of the birth experience, level of exhaustion during the first year, and relationship stress, are not available in our survey data and are better suited to qualitative work [...]," they add. "Therefore, this research should be read alongside qualitative work."
Still, based on their findings, the team says policy-makers in developed countries who have concerns about low fertility rates should consider how the wellbeing of first-time parents impacts future fertility.
Earlier this month, Medical News Today reported on a study published in the Journal of Epidemiology & Community Health in which researchers found men who become fathers before the age of 25 may be at greater risk of death in middle age.