Past evidence on fertility responses to external shocks, including economic recessions and the outbreaks of infectious diseases, show that people often put their childbearing plans on hold in uncertain times. We study the most recent data on monthly birth trends to analyse the initial fertility responses to the outbreak of the COVID-19 pandemic. Our research, based on new Short-Term Fertility Fluctuations (STFF) data series (https://www.humanfertility.org/cgi-bin/stff.php), embedded in the Human Fertility Database (HFD), shows the initial signs of the expected “birth recession”. Monthly number of births in many countries fell sharply between October 2020 and the most recent month observed, often bringing about a clear reversal of the previous trend. Across 17 countries with lower fluctuations in births, the number of births fell on average by 5.1% in November 2020, 6.5% in December 2020 and 8.9% in January 2021 when compared with the same month of the previous year. Spain sustained the sharpest drop in the number of births among the analysed countries, with the number of births plummeting by 20% in December 2020 and January 2021. The combined effect of rising mortality and falling birth rates is disrupting the balance of births and deaths in many countries, pushing natural population increase to record low levels in 2020 and 2021.