Hello, me again. I don't want to sound alarmist, but I spent this morning reading through the actual research the RCOG advice is based on (apologies, but I'm a researcher - albeit not a medical one). I feel really uncomfortable about their approach. It is true that none of the very limited research on COVID19 in pregnancy has identified a specific increased risk of miscarriage, but there doesn't actually seem to be any research on this specific issue. So I can't see how they are ruling this out.
Meanwhile, although the RCOG guidance says that 'Case reports from early pregnancy studies with SARS and MERS [two much more lethal types of coronavirus] do not demonstrate a convincing relationship between infection and increased risk of miscarriage or second trimester loss', the actual study they cite to back up this claim is only of five patients (Zhang J, Wang Y, Chen L, et al. Clinical analysis of pregnancy in second and third trimesters complicated severe acute respiratory syndrome. Zhonghua Fu Chan Ke Za Zhi 2003;38:516-20). However a more recent review (Potential Maternal and Infant Outcomes from Coronavirus 2019-nCoV (SARS-CoV-2) Infecting Pregnant Women: Lessons from SARS, MERS, and Other Human Coronavirus Infections, by Schwartz and Graham, 2020) details several studies and concludes that there may be potential risks to both the mother and the child. A study of 7 women in their first trimester with SARS, for example, found that four had a miscarriage, and for those later than 24 weeks 4 had preterm deliveries.
A case series of 10 women with COVID 19 concluded 'Perinatal 2019-nCoV infection may have adverse effects on newborns, causing problems such as fetal distress, premature labor, respiratory distress, thrombocytopenia accompanied by abnormal liver function, and even death. However, vertical transmission of 2019-nCoV is yet to be confirmed.' (Clinical analysis of 10 neonates born to mothers with 2019-nCoV pneumonia, by Huaping Zhu and colleagues).
It feels to me that there are good reasons to be more cautious than the general population as you go about your business, unless more robust evidence emerges that there isn't a more severe risk to pregnancies (and pregnant mothers). It feels to me that they are applying a scientific paradigm of 'we won't advise caution unless there is really strong evidence of a risk', at a time when a more cautious paradigm should be adopted given what we know about the risks of other coronaviruses and also more generally conditions like flu and pneumonia that cause respiratory problems, fevers and can indeed be harmful in pregnancy.
What do others think? Just to reiterate one more time, I am not a medical researcher.