Like everything in this pandemic, the knowledge we have about how COVID-19 affects pregnancy has changed since we first learnt about the virus at the start of 2020.

Unfortunately, gathering information and research in this area has been slower than many doctors would like, and a new study has now found that pregnancy risks could be greater than what we thought.

"We now know that the risks to mothers and babies are greater than we assumed at the start of the pandemic and that known health measures when implemented must include pregnant women," said University of Oxford reproductive medical researcher Stephen Kennedy, one of the study authors.

"The information should help families, as the need to do all one can to avoid becoming infected is now clear. It also strengthens the case for offering vaccination to all pregnant women."

The researchers followed 2,130 pregnant women from 18 countries between March and October 2020, 706 of them having been diagnosed with COVID-19 and the rest without, as part of a study called INTERCOVID.

For each pregnant woman who was infected with COVID-19, the team then enrolled two pregnant women from the same hospital at the same pregnancy stage and followed them all until the birth and discharge from hospital.

The study was observational, so it can only inform us about the potential links between COVID-19 and pregnancy risks, but the results are consistently worse for those pregnant women with COVID-19.

"This is a great study," University of Montreal Hospital Research Centre epidemiologist Nathalie Auger, who was not involved in the study, told Science.

"They followed women through pregnancy, which is a really great design, and helped confirm the previous studies that are much easier to critique."

The research found that pregnant women with a SARS-CoV-2 infection were at a higher risk for severe infections, intensive care unit admissions, and even death. Babies were also significantly more likely to be preterm and have other complications.

"Women with COVID-19 during pregnancy were over 50 percent 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," says Oxford fetal medicine researcher and study co-author Aris Papageorghiou.

"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," he adds, "is that the risks in symptomless infected women and non-infected women were similar."

This is important information for those who currently are, or are looking to get pregnant. We've already seen the virus may sometimes be passed from mother to baby, and this study adds to that body of research, finding 13 percent of babies with COVID-19 positive moms also tested positive in the first few days after birth.

Interestingly, the research team also found that caesarean delivery was associated with a higher risk of babies testing positive to the virus, while breastfeeding was not.

This is unlikely to be the last word on this topic, but the research provides much needed clarity for those expecting or considering becoming pregnant while the pandemic continues, and is also valuable information for the authorities managing vaccination programs.

And for those that do contract COVID-19 while pregnant, doctors will have more information to make sure they have a healthy pregnancy and delivery.

The research has been published in JAMA Pediatrics.