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\begin{document}

\title{Changes in Conception Rates, Not in Pregnancy-Related Behavior, Likely
Caused Decline in Pre-Term Births During the First Year of the COVID-19
Pandemic}



\author[1]{Peter Fallesen}%
\author[2]{Moritz Oberndorfer}%
\author[3]{Marco Cozzani}%
\affil[1]{Stockholms Universitet}%
\affil[2]{Medizinische Universitat Wien Zentrum fur Public Health}%
\affil[3]{Universita degli Studi di Firenze Dipartimento di Statistica Informatica Applicazioni Giuseppe Parenti}%


\vspace{-1em}



  
  \date{May 19, 2024}


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\textbf{Changes in Conception Rates, Not in Pregnancy-Related Behavior,
Likely Caused Decline in Pre-Term Births in Developed Countries During
the First Year of the COVID-19 Pandemic} 11\textsuperscript{*}
Corresponding author: Peter Fallesen, peter.fallesen@sofi.su.se, Swedish
Institute for Social Research, Stockholm University, Stockholm 106 91,
Sweden.

Peter Fallesen, PhD

\emph{Swedish Institute for Social Research,} \emph{Stockholm
University, Stockholm 106 91, Sweden ROCKWOOL Foundation, Ny Kongensgade
6, 1472 Copenhagen C, Denmark}

Moritz Oberndorfer, DSc ~

\emph{Institute of Social Medicine, Center for Public Health, Medical
University of Vienna, Kinderspitalgasse 15/1. Stock, A-1090, Vienna,
Austria; MRC/CSO Social and Public Health Sciences Unit, University of
Glasgow, Berkeley Square, 99 Berkeley Street, Glasgow, G3 7HR, UK
~Population Research Unit, University of Helsinki, Unioninkatu 35 (P.O.
Box 18). 00014 University of Helsinki, Finland} ~

Marco Cozzani, PhD

\emph{Population and Society Research Unit, Department of Statistics,
Computer Science, Application ``Giuseppe Parenti''(DiSIA), University of
Florence, Viale Giovanni Battista Morgagni 59, 50134 Firenze, Italy}

Running head: Conception Rates Caused Decline in Pre-Term Births During
the COVID-19 Pandemic\emph{}

{A series of studies, including recent work published in BJOG by Rusconi
et al.}\textsuperscript{1}, has highlighted the surprising fact that
measures of birth outcomes such as pre-term birth and low birth weight
improved nine months after the first wave (February-June 2020) of ~the
COVID-19 pandemic across countries such as Italy, Spain, Ireland, and
the United States (see Yang et al.\textsuperscript{2} for recent meta
study). This growing body of work has generated important knowledge on
the children conceived and born during the pandemic, and how they as a
cohort may differ from those born before and after the pandemic. Yet, we
believe that this strand of literature has overlooked key demographic
drivers behind the changes in birth outcomes observed during the
pandemic. Here {we describe why an improvement in birth outcomes
observed during the pandemic is likely caused by decline in conception
rate and changing selection into conception in the months following the
onset of the pandemic rather than changing behaviors among pregnant
women during the pandemic.}

{}

In their BJOG article, {Rusconi et al.}find that rates of pre-term
births declined drastically in September-November 2020 relative to
trend, and they ask researchers to consider what lessons the pandemic
may teach about~ the ``possible importance of lifestyle and
environmental aspects related to the occurrence of pregnancies ending
preterm''\textsuperscript{1 p. 282}. Others have noted the non-causal
nature of these studies\textsuperscript{3}, which should be kept in mind
for future research to cover. We, however, suggest a more fundamental
aspect of the pandemic's effect on pregnancies has been overlooked
broadly in the literature, which can account for most, if not all, of
the decline found by Rusconi et al. and many other studies. The cause of
decline in pre-term births and other adverse birth outcomes should not
necessarily be sought in {changing behavior or services during
pregnancy, but rather in changes in how many and who conceived during
the early stages of the pandemic}\textsuperscript{4,5}, as declines in
conceptions and subsequent fertility rates have been observed across
most developed countries.\textsuperscript{6}

Figure 1 shows the monthly crude birth rate (CBR; number of births per
1,000 population) for Italy for 2020 and 2021 measured relative to the
2019 monthly CBR. As clearly seen from the figure, number of births
declined drastically relative to 2019 starting September 2020 and until
January 2021, with the CBR in January 2021 being 14\% lower than what
was observed in January 2019, which is the equivalent of 8.4 fewer
births per 100,000 population that month. Rapidly declining birth rates
are mostly caused by rapidly declining conception rates and are unlikely
to be only explained by potential changes in pregnancy loss, abortion,
maternal emigration, and stillbirth rates. Mechanically, a decline in
conceptions will manifest first as a decline in preterm births 7-8
months after the number of conceptions dropped.\textsuperscript{4} This
is because (fewer) pre-term babies, which were conceived after the
pandemic onset, are born at the same time as full-term babies conceived
before the COVID-19 pandemic. Thus, the decline in pre-term rates can be
seen as a demographic artifact caused by declining conceptions without
any change to pregnancy-related behavior occurring. In recent work, we
have shown that a similar trend in fertility can be observed in Spain
for the same period.\textsuperscript{4,7} In this work, we also show a
similar decline in Spanish preterm births rates as observed in Italy by
Rusconi et al.\textsuperscript{4} Further, we demonstrate how this
decline in preterm births can occur mechanically in the case of a rapid
decline in conceptions right after the onset of the COVID-19 pandemic,
which in turn leads to the observed lower birth rates beginning by
September (fewer pre-term births) and carrying out all through to
January 2021 (fewer at term births).

~~~~~~~~~~~ {[}Figure 1 about here.{]}

Further, we also analyze changes in who conceive. In the Spanish case
the data allows us to examine which groups see the largest conception
declines. In relative terms, the two groups that sees the largest
decline are women at the beginning and end of the reproductive age---the
two groups also at highest risk of giving birth to preterm babies
because of, respectively, precarious and unplanned pregnancies occurring
among the young\textsuperscript{8} and higher rates of complications and
medically assisted reproductive (MAR) conceptions among the older
women.\textsuperscript{9} During the first COVID-lockdown young people's
risk for precarious and unplanned pregnancies declined drastically due
to stay-at-home orders, and MAR clinics shut down services. Moreover,
the COVID-19 pandemic has likely led to changes in the composition of
parents in regards to other characteristics known to be associated with
preterm birth.\textsuperscript{5} For example, initial evidence is
emerging that babies conceived in the Global North during the pandemic
have, on average, more socioeconomically advantaged parents than babies
conceived before the COVID-19 pandemic.\textsuperscript{5,10} More
advantaged parental socioeconomic circumstances, in turn, have
consistently been shown to be associated with a lower probability of
preterm birth.\textsuperscript{11} Pandemic-induced compositional shifts
in parental characteristics provide us with another plausible
explanation for improved birth outcomes during the COVID-19 pandemic in
the Global North, whereas the situation in countries with less universal
access to contraceptive measures may have seen different developments,
as suggest by, e.g., Pesando and Abufhele\textsuperscript{12} for Chile.

To conclude, the COVID-19 pandemic may have generated a pure demographic
artifact driven by a population wide decline in conceptions discussed
above as well as heterogenous conceptive responses across the affected
populations. These two differential effects of the COVID-19 pandemic may
also explain why babies conceived during the pandemic show improved
birth outcomes compared with babies conceived before the pandemic. When
interpreting the COVID-19 consequences on newborns health we thus advice
to disentangle the direct effect of in utero exposure to the COVID-19
pandemic and the consequences of lockdown measures on birth outcomes
from a demographic artifact and pandemic-induced changes in composition
of who became pregnant. Importantly, the latter determinants and the
former ones may have different clinical implication for the population
of newborn and their long-term development trajectories.

\par\null

\textbf{Acknowledgements}

Peter Fallesen was a visiting fellow at Department of Political and
Social Sciences, European University Institute during the writing of
this commentary.

\textbf{~}

\textbf{Disclosure of Interests}

The authors have no interest to declare.

~

\textbf{Contribution to Authorship}

PF, MO, and MC conceived, planned, carried out, analyzed, and wrote up
the manuscript. All authors approved final version.

~

\textbf{Details of Ethics Approval}

Only publicly available secondary data used for analysis so exempt for
ethical approval.

~

\textbf{Funding}

PF's work was supported by ROCKWOOL Foundation (1227) and the Swedish
Research Council for Health, Working Life and Welfare (2016--07099).
MO's work was supported by the Medical Research Council
(MC\_UU\_00022/2) and the Scottish Government Chief Scientist Office
(SPHSU17). MC's work was supported by the Italian Ministry of the
University and Research (PE8- B83C22004800006).

\textbf{~}

\textbf{References}

1. ~~~~~~~ Rusconi F, Puglia M, Pacifici M, Brescianini S, Gagliardi L,
Nannavecchia AM, et al. Pregnancy outcomes in Italy during COVID-19
pandemic: A population-based cohort study. BJOG: An International
Journal of Obstetrics \& Gynaecology. 2023;130(3):276--84.

2. ~~~~~~~ Yang J, D'Souza R, Kharrat A, Fell DB, Snelgrove JW, Shah PS.
COVID-19 pandemic and population-level pregnancy and neonatal outcomes
in general population: A living systematic review and meta-analysis
(Update\#2: November 20, 2021). Acta Obstetricia et Gynecologica
Scandinavica. 2022;101(3):273--92.

3. ~~~~~~~ Sisti G, Joseph JT. Reduction in preterm birth rate during
the COVID-19 pandemic: Analysing causation. BJOG: An International
Journal of Obstetrics \& Gynaecology. 2023;130(3):285--285.

4. ~~~~~~~ Cozzani M, Fallesen P, Passaretta G, H\selectlanguage{ngerman}ärkönen J, Bernardi F.
The Consequences of the COVID-19 Pandemic for Fertility and Birth
Outcomes: Evidence from Spanish Birth Registers. Population and
Development Review. 2023;Early View.

5. ~~~~~~~ Oberndorfer M, Dundas R, Leyland AH, Pearce A. The LoCo
(Lockdown Cohort)-effect: why the LoCo may have better life prospects
than previous and subsequent birth cohorts. European Journal of Public
Health. 2022 Jun 1;32(3):339--40.

6. ~~~~~~~ Sobotka T, Zeman K, Jasilioniene A, Winkler-Dworak M,
Brzozowska Z, Alustiza-Galarza A, et al. Pandemic Roller-Coaster? Birth
Trends in Higher-Income Countries During the COVID-19 Pandemic.
Population and Development Review {[}Internet{]}. 2023 {[}cited 2023 May
10{]};OnlineFirst. Available from:
https://onlinelibrary.wiley.com/doi/abs/10.1111/padr.12544

7. ~~~~~~~ Fallesen P, Cozzani M. Partial Fertility Recuperation in
Spain Two Years After the Onset of the COVID-19 Pandemic {[}Internet{]}.
SocArXiv; 2023 {[}cited 2023 Jan 12{]}. Available from:
https://osf.io/preprints/socarxiv/2m5pr/

8. ~~~~~~~ Gipson JD, Koenig MA, Hindin MJ. The Effects of Unintended
Pregnancy on Infant, Child, and Parental Health: A Review of the
Literature. Studies in Family Planning. 2008;39(1):18--38.

9. ~~~~~~~ Goisis A, Remes H, Martikainen P, Klemetti R, Myrskylä M.
Medically assisted reproduction and birth outcomes: a within-family
analysis using Finnish population registers. The Lancet. 2019 Mar
23;393(10177):1225--32.

10. ~~~~~ Lappegård T, Kornstad T, Dommermuth L, Kristensen AP.
Understanding the Positive Effects of the COVID-19 Pandemic on Women's
Fertility in Norway. Population and Development Review. 2023;Early View.

11. ~~~~~ Thomson K, Moffat M, Arisa O, Jesurasa A, Richmond C, Odeniyi
A, et al. Socioeconomic inequalities and adverse pregnancy outcomes in
the UK and Republic of Ireland: a systematic review and meta-analysis.
BMJ Open. 2021 Mar 1;11(3):e042753.

12. ~~~~~ Pesando LM, Abufhele A. Declining Quantity and Quality of
Births in Chile amidst the COVID-19 Pandemic. Population and Development
Review. 2023;Early View.



\par\null

\textbf{Figure 1.} Monthly Crude Birth Rate for Italy 2020-2021 Measured
Relatively to the Monthly Crude Birth Rate in 2019.

Source: ISTAT.\selectlanguage{english}
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