The guidelines for the management of pregnant women admitted for delivery have regularly been updated concerning the evolution of the COVID-19 pandemic from the first to second and following waves [8]. Initially, screening of pregnant women admitted for hospitalization or delivery in Slovenia focused on travel history and the presence of COVID-19-compatible symptoms. Nevertheless, it soon became clear that, in addition to a screening questionnaire, determining the SARS-CoV-2 status using RT-PCR and/or RAT is necessary to apply isolation measures, enable rational use of Personal Protective Equipment (PPE), and prevent transmission of the virus [8]. Testing of all pregnant women admitted for a planned procedure or hospitalization using RT-PCR was possible during the first wave due to a relatively low burden of SARS-CoV-2 in the Slovenian population [3]. However, skyrocketing numbers of new SARS-CoV-2 cases and escalating demands for SARS-CoV-2 testing at the beginning of the second wave considerably challenged the timely availability of RT-PCR testing results in obstetric units. In addition, scaled-up RT-PCR testing at a national level somewhat prolonged the time-to-result, and limited supplies of testing reagents as well as a lack of highly trained laboratory personnel hindered universal RT-PCR testing of all pregnant women admitted to our hospital. Because of a much higher likelihood of being infected with SARS-CoV-2 compared to the first wave, the hospital’s screen-and-test approach had to be adapted accordingly during the second wave. Thus, RAT with Sofia SARS Antigen FIA was implemented on 27 October 2020 to enable rapid triage of pregnant women admitted for a planned procedure or hospitalization. Analyzer-based Sofia SARS Antigen FIA provides automated results within 15 minutes with 96.7% positive and 100% negative percent agreement with RT-PCR, according to the manufacturer data [4]. However, in real-life settings, the sensitivity, and specificity of the antigen test may be considerably lower and largely depend on the pre-test probability (e.g., asymptomatic vs. symptomatic; time since exposure) [9]. Despite the arguably lower analytical sensitivity and specificity of RAT compared to RT-PCR, RAT still allows rapid identification of infectious individuals and the potential earlier breaking of transmission chains [9]. Before the introduction of RAT in our Maternity Hospital, there were two instances of SARS-CoV-2 positive pregnant women being brought into the “white zone” (e.g., COVID-19 free zone) of the labour ward. One woman was asymptomatic, while the other denied any symptoms in the screening questionnaire she had filled out upon admission but became symptomatic later during the hospitalization.

In contrast to the first wave, screening and testing of all women admitted for delivery also became mandatory during the second wave. For this purpose, rapid antigen testing with Sofia SARS Antigen FIA was available 24/7. Namely, in addition to the symptomatic women, it is crucial to identify with regular testing also SARS-CoV-2 infected but asymptomatic women before they enter the delivery rooms allocated for COVID-19-negative patients. Potential intrusions into the “white zone“ are especially problematic during the birth process because of the potential risk for horizontal transmission to other mothers and new-borns within multiple-bed rooms. If RAT performed before delivery is negative, it is relatively safe for the staff to be in contact with a woman in labour for at least some time (possibly up to 24 hours), although testing should be immediately repeated if symptoms develop after initial testing or in case of confirmed SARS-CoV-2 infection among close contacts. In this study, only 20/26 (76.9%) of asymptomatic pregnant women that were RAT-positive were subsequently confirmed to be RT-PCR-positive. Hence, we believe that confirmation of a positive RAT result in asymptomatic pregnant women with RT-PCR is warranted. Our previous screen-and-test study performed during the first COVID-19 wave did not support universal SARS-CoV-2 RT-PCR testing since we had not identified a single new SARS-CoV-2-positive case among asymptomatic and even symptomatic pregnant women scheduled for a planned procedure at our institution [3]. In contrast, the current study clearly identified the benefit of universal screening and testing in settings with high SARS-CoV-2 burden. Because previous reports showed high rates (up to 89%) of asymptomatic SARS-CoV-2 infections among pregnant women [10,11], universal laboratory testing may provide a more accurate estimation of the prevalence of the disease in this population than screening for the presence of COVID-19 compatible symptoms using questionnaire only [12]. In addition, identifying SARS-CoV-2-positive women before delivery has several important clinical implications, including triage, allocation of appropriate resources (e.g., delivery ward, operating theatre) and PPE, transfer between hospitals, postpartum rooming-in, and neonatal care [13]. Universal SARS-CoV-2 testing of pregnant women should be preferably performed using clinically validated RT-PCR-based assays. However, despite its inferior analytical performance, testing with RAT may be an efficient tool for determining the SARS-CoV-2 status of pregnant women, providing that universal RT-PCR testing is unattainable. If rapid antigen testing is considered, a choice of the appropriate test is crucial, since a recent comparative evaluation of 122 CE-marked SARS-CoV-2 RATs showed that the sensitivity of different RATs varied over a wide range with potentially serious clinical consequences [14].

Whereas only two women were actively infected with SARS-CoV-2 at the time of delivery during the initial 1.5-month surveillance period during the first COVID-19 wave in Slovenia [3], a total of 119 deliveries needed to be carried out in a separate COVID-19 labour ward during the second surveillance period.

For a few days in November 2020, all three SARS-CoV-2 delivery wardrooms were always occupied. In addition, all five beds in the intensive care unit were occupied for rooming-in SARS-CoV-2-positive mothers and their new-borns; however, despite the heavy workload of the medical and support staff, we were able to perform all work needed without opening additional wards.

Our study has several limitations. We analysed a relatively short period (four months) and included data from a single center only. However, our Maternity Hospital is the biggest tertiary perinatal center in Slovenia, with almost 1/3 of all deliveries in the country (around 5,500 deliveries per year), accepting also in-utero transfers up to 34 gestational weeks as well as otherwise high-risk pregnant women from all other 13 obstetrical units within our country. Because of the study design we were, unfortunately, not able to evaluate the proportion of SARS-CoV-2 infected pregnant women that were missed due to using a screening test with inferior sensitivity compared to RT-PCR. However, in our evaluation, none of the RAT-negative women became symptomatic in the immediate postpartum period or hospitalization, suggesting triage with RAT may provide sufficient protection in most cases.