Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Oct 20;9(1):374-382.
doi: 10.1093/emph/eoab033. eCollection 2021.

Twinning during the pandemic: Evidence of selection in utero

Ralph Catalano  1 , Tim Bruckner  2 , Joan A Casey  3 , Alison Gemmill  4 , Claire Margerison  5 , Terry Hartig  6
Affiliations

Twinning during the pandemic: Evidence of selection in utero

Ralph Catalano et al. Evol Med Public Health. .

Abstract

Background and objectives: The suspicion that a population stressor as profound as the COVID-19 pandemic would increase preterm birth among cohorts in gestation at its outset has not been supported by data collected in 2020. An evolutionary perspective on this circumstance suggests that natural selection in utero, induced by the onset of the pandemic, caused pregnancies that would otherwise have produced a preterm birth to end early in gestation as spontaneous abortions. We test this possibility using the odds of a live-born twin among male births in Norway as an indicator of the depth of selection in birth cohorts.

Methodology: We apply Box-Jenkins methods to 50 pre-pandemic months to estimate counterfactuals for the nine birth cohorts in gestation in March 2020 when the first deaths attributable to SARS-CoV-2 infection occurred in Norway. We use Alwan and Roberts outlier detection methods to discover any sequence of outlying values in the odds of a live-born twin among male births in exposed birth cohorts.

Results: We find a downward level shift of 27% in the monthly odds of a twin among male births beginning in May and persisting through the remainder of 2020.

Conclusions and implications: Consistent with evolutionary theory and selection in utero, birth cohorts exposed in utero to the onset of the COVID-19 pandemic yielded fewer male twins than expected.

Lay summary: Our finding of fewer than expected male twin births during the onset of the COVID-19 pandemic provides more evidence that evolution continues to affect the characteristics and health of contemporary populations.

Keywords: COVID-19; selection in utero; twins.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
Observed (circles) and expected (x’s) monthly logged odds of a twin among male infants born in Norway from January 2016 through November 2020. Filled circles show outlying sequence
Figure 2.
Figure 2.
Observed (circles) and expected (x’s) monthly logged odds of a twin among female infants born in Norway from January 2016 through November 2020. Filled circle shows outlying value
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Lima SAM, El Dib RP, Rodrigues MRK et al. Is the risk of low birth weight or preterm labor greater when maternal stress is experienced during pregnancy? A systematic review and meta-analysis of cohort studies. PLoS One 2018;13:e0200594. - PMC - PubMed
    1. Chmielewska B, Barratt I, Townsend R et al. Effects of the COVID-19 pandemic on maternal and perinatal outcomes: a systematic review and meta-analysis. Lancet Glob Health 2021;9:e759–e772. - PMC - PubMed
    1. De Curtis M, Villani L, Polo A. Increase of stillbirth and decrease of late preterm infants during the COVID-19 pandemic lockdown. Arch Dis Child Fetal Neonatal Ed 2021;106:456. - PMC - PubMed
    1. Wasser SK, Barash DP. Reproductive suppression among female mammals: implications for biomedicine and sexual selection theory. Q Rev Biol 1983;58:513–538. - PubMed
    1. Mock DW, Forbes LS. The evolution of parental optimism. Trends Ecol Evol 1995;10:130–134. - PubMed