Pregnant women with symptomatic COVID-19 are more at risk of severe complications - as are their newborns - if they do not have access to "comprehensive ICU services", a worldwide study has found.
The research from the United States, involving more than 35,000 women, also suggested that expectant mothers who have a Pfizer or Moderna vaccine are no more likely to suffer miscarriage, premature birth or other complications than women before the pandemic.
These two vaccines were examined as they are the ones which have been administered the most in the country.
Advice from the Royal College of Obstetricians and Gynaecologists (RCOG) states that, in the UK, women should be offered the Pfizer or Moderna jab if possible - but this is due to a lack of data on other vaccines as the US has provided most of the research.
The new research on the coronavirus-positive expectant women has seen scientists from the University of Oxford conclude that "health priority measures should include pregnant women" after seeing a higher mortality rate in those in the group who have symptomatic COVID-19.
While the study did find a mortality rate of 1.6% for pregnant women with the coronavirus - around 22 times higher than expectant mothers without COVID - these were mostly in cases in less developed regions, implying that a lack of comprehensive intensive care facilities could lead to the possibility of coronavirus during pregnancy being lethal.
Advice from the RCOG states: "Roughly two-thirds of pregnant women with COVID-19 have no symptoms at all, and most pregnant women who do have symptoms only have mild cold or flu-like symptoms."
The RCOG goes on to say that any symptoms should be reported to a midwife, and further medical help should be sought if they worsen.
The research included results from 18 different countries, and compared cases with COVID-negative women who were in the same hospital and delivering at the same time.
Aris Papageorghiou, professor of foetal medicine at the University of Oxford, who co-led the study, said: "Women with COVID-19 during pregnancy were over 50% more likely to experience pregnancy complications (such as premature birth, pre-eclampsia, admission to intensive care and death) compared to pregnant women unaffected by COVID-19.
"Newborns of infected women were also nearly three times more at risk of severe medical complications, such as admission to a Neonatal Intensive Care Unit - mostly due to premature birth.
"The good news, however, is that the risks in symptomless infected women and non-infected women were similar."
The study found that almost 10% of newborns from COVID-positive mothers also tested positive for the disease.
Jose Villar, professor of perinatal medicine at the University of Oxford, who co-led the study, said: "Importantly, breastfeeding does not seem to be related to this increase.
"Delivery by caesarean section, however, may be associated with an increased risk of having an infected newborn."