When the SARS-Cov-2 pandemic was officially declared in March 2020 and the world went into lockdown, demographers and the greater public alike speculated about how this unprecedented situation would impact fertility and family dynamics. You probably remember the headlines. The media predicted either a baby boom from couples quarantining together, or feared a baby bust driven by health risks, economic recessions, disrupted relationships, and ubiquitous stresses.

As demographers, we understood the complexities of potential links between fertility or family dynamics and the pandemic in a more nuanced way. We knew for instance from previous studies that changes in fertility (if it does change) following disasters can vary depending on the type of disaster, its location, the affected populations, and the specific ways they are impacted. Still, we were curious about the potential impacts of the COVID-19 pandemic on fertility dynamics at the population level. To stimulate research on this topic, we (Natalie Nitsche, Joshua Wilde, and Mikko Myrskylä), the guest editors, in collaboration with Population and Development Review, organized a scientific conference in December 2021 and issued a call for papers for a forthcoming supplement in that journal.

Now, four years after the pandemic began, the “pandemic babies” have grown into toddlers and preschoolers. What insights have we gained about the pandemic’s impact on fertility dynamics? Based on the evidence in this supplement and the wider literature in the field, we’ve arrived at three main conclusions:

The Pandemic Delivered Unexpected Heterogeneities

The studies clearly demonstrate substantial variation in both fertility behavior and fertility ideation responses to the pandemic across societies, time periods, and population subgroups, indicating multifaceted heterogeneity that few of us expected. For instance, early findings documented moderate to large pandemic-driven birth declines across Southern Europe and the US about ten months after the pandemic started—a finding that contributed to a “pandemic baby bust” narrative. However, later data revealed stable rates across Central Europe and low- and middle-income countries, and positive responses in some Scandinavian countries in the early pandemic. This was followed by rollercoaster-like birthrate ups and downs in many societies as the pandemic progressed. Moreover, we learned that the fertility response varied by social groups. Yet how this variation looked also depended on the social context. In the US, for instance, the early birth rate declines were concentrated among foreign-born women, while in Spain they were concentrated among the non-college educated and on first births. We also learned that welfare systems and social distancing measures appear to have played a role for the pandemic’s fertility response, but many open questions about the drivers of the various heterogeneities documented in this volume remain.

Beyond birth rates, the pandemic’s impact on other reproductive outcomes such as preterm births and low birthweight, as well as on fertility ideation, also varied across countries. This suggests a more comprehensive understanding of the reproductive process is needed to fully grasp how pandemic-induced changes altered reproductive outcomes and plans.

There is Insufficient Data to Answer Basic Questions

Accurately measuring the pandemic’s impact on the full reproductive process—from sexual behavior to conception to pregnancy outcomes, and social-group variation therein—requires large samples across numerous contexts over time. While administrative birth registers are available in high-income countries, they typically offer data on birth counts only. Furthermore, they are much scarcer in low- and middle-income countries. This leads to a lack of comprehensive data on the reproductive process and fertility. Even excellent administrative data often can’t depict important contextual factors. To further the understanding of what exactly happened to fertility and family dynamics since the onset of the pandemic, and why we observe the variations we do, we will need to keep developing multiple data sources going forward.

Unclear Pandemic Effects Due to Ambiguous Baselines and Causality Issues

Finally, we learned that interpreting the pandemic’s “effect” on demographic measures is challenged by the lack of a clear pre-pandemic baseline, given rapidly shifting fertility across regions in pandemic-preceding years. The exceptional and still poorly understood developments in fertility trajectories prior to the pandemic prevent the construction of a realistic counterfactual.

To complicate the picture further, disentangling the pandemic’s specific “causal impact” is extremely difficult given the multitude of unprecedented social and economic shocks during 2020-22 that could plausibly shape reproductive behavior through various mechanisms. The circumstances and policies created during the pandemic may be linked to fertility and family dynamics, making it even more challenging to understand what exactly triggered the changes in fertility, which were, if they occurred, often short lived. We therefore conclude it is advisable to avoid using causal language of the ‘pandemic effect’ and causal interpretations.

In sum, this supplement and the excellent articles in it teach us various lessons:

Population scientists need comprehensive data on the reproductive and family processes and can benefit from embracing novel theoretical demographic and methodological approaches, including qualitative methodologies.

While many insights on post-pandemic fertility and family dynamics were gained, the understanding is still incomplete. The seemingly negative “impact” observed across various societies in response to the first pandemic wave is not generalizable to other regions, later phases of the pandemic, or, even if occurring, all social groups.

It is difficult to find appropriate baselines to measure pandemic effects, given the complexities of population processes.

Despite these challenges, the studies in this volume are stage-setting. Solving the puzzling pandemic fertility and fertility ideation patterns they and other studies documented promises a rich stream of future research for years to come. The volume also underscores what demographers can gain by rethinking data, theoretical framings, and methodological approaches to disentangling causality amid complexity. Thank you to all involved in making this volume come to life, and happy reading to everyone else!