Discussion
Reassuringly, multiple studies have now shown that relatively few pregnant women have been significantly affected by coronavirus (1–4). However, several studies have suggested that a significant number of pregnant women can have asymptomatic SARS-CoV2 infection. Universal testing of all maternity admissions in one study in the USA found 23/635 (4%) women were positive for SARS-CoV2, but 10/23 (43%) of those positive denied any symptoms at time of screening (5);another study of 307 women admitted in labour found 50/307 (16%) were asymptomatic (6).
Our study shows a low prevalence of SARS-CoV2 in pregnant women, with only 18/593 (3%) women being positive. However, our rate of asymptomatic infection was low; only 3/18 (17%) had no symptoms when screened. Two of these three women (66%) had had symptoms of COVID-19 in the preceding 2 weeks, and the third woman was screened as another household member was SARS-CoV2 positive. The discrepancy between our results and the above screening studies may reflect that their women were only asked about symptoms at the time of screening rather than in the preceding days. In addition, two women initially denied any symptoms, until they were objectively found to have a fever in labour. This may perhaps have been due to concerns about differential treatment in hospital if they were SARS-CoV2 positive as has been shown in some reports (7). This behaviour may similarly affect the numbers of women reported as asymptomatic in other studies. Furthermore, in our study, enhanced screening of asymptomatic women started eight weeks in to ‘lockdown’. By this point, the prevalence of SARS-CoV2 in the general population was falling, and may explain the low numbers of cases detected compared to other studies where universal screening was initiated earlier.
The fall in cases over the weeks of the study reflects the successful ‘lockdown’ and ‘shielding’ advice given to pregnant women within the UK. However, as restrictions are lifted, it is possible if not likely that there will be an increase in the number of SARS-CoV2 cases. Of particular concern at the moment is the risk of localised outbreaks, for example among otherwise healthy women attending antenatal clinics, or within a staff group in a maternity centre (outbreaks within hospital staff groups have been reported in social media). Given these factors, we would suggest all obstetric units in the UK instigate and continue universal screening of women being admitted to hospital. However if this is not available and screening has to be targeted, from our data we would recommend an extended questionnaire, to ensure screening includes women who are both currently symptomatic and those who have had symptoms in the last 3 weeks, and women who have had contact with anyone else who has been symptomatic in the last two weeks.