Danish researchers study how susceptible pregnant women are to COVID-19

Breaking new ground 13. okt 2020 5 min Postdoc, Registrar Stine Yde Nielsen Written by Anne Jensen Sand

Knowledge about how susceptible expectant mothers are to SARS-CoV-2 infection is still sparse, but several international studies indicate that they do not constitute an especially susceptible group. A study of several hundred women giving birth in Denmark’s hospital system found that few had COVID-19. The explanation may be self-isolation during pregnancy.

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When SARS-CoV-2 arrived in Denmark, the population was immediately put into groups depending on how sick, susceptible or indispensable to Denmark’s cohesion and economy they were.

Some people were immediately sent home, and others had to maintain physical distancing at their workplace and became even busier, such as doctors and social and healthcare assistants in Denmark’s hospitals and nursing homes. People with chronic illness were classified as highly susceptible to contracting COVID-19 and vulnerable to severe illness if they got it, but young and healthy people were not a concern. Then there were pregnant women, who in addition to worrying about their baby’s well-being were also supposed to be cautious about COVID-19, the consequences of which they did not know much about.

“The Danish Health Authority categorized pregnant women as being at increased risk of severe COVID-19. They did this based on a precautionary principle for the sake of the pregnant woman and the unborn child, but the Authority’s website said that no evidence supports this. Reasonably robust evidence now indicates that the risk of severe COVID-19 increases with age and various chronic diseases. However, knowledge is still lacking about other high-risk groups, such as pregnant women,” says Stine Yde, Registrar in Clinical Microbiology and Postdoctoral Fellow at the Department of Biomedicine, Aarhus University.

Obtaining samples carefully

Since the end of April, Stine Yde and several colleagues have examined 800 mothers and their newborn babies in the maternity wards at Aarhus University Hospital, Kolding Hospital and Lillebælt Hospital to investigate the mothers’ COVID-19 symptoms, become more knowledgeable about the process of women with COVID-19 giving birth and to determine whether the virus can be transmitted from mother to child, as other microbes can. This applies, for example, to group B streptococci, with which the baby can be infected on the way out of the birth canal if the mother has bacteria in the intestines or birth canal.

Stine Yde explains that, when the women go into labour, they are inoculated in the pharynx, vagina and rectum and then have a blood sample taken. Instead of taking blood from the newborn, blood is taken from the umbilical cord. Giving birth is a vulnerable time, and researchers should therefore be as unobtrusive as possible, so no blood samples are taken directly from the baby.

“We also take a sample from the baby’s nose, which is a simple and quick procedure. If SARS-CoV-2 has crossed the placenta, which is supposed to protect the baby from infections, then it would probably be present in both the amniotic fluid and the baby’s nose. All these tests provide a snapshot of whether the mother and child have COVID-19 and help to determine when they got infected,” says Stine Yde.

Few pregnant women have COVID-19

For many people, COVID-19 has become a worrying but also routine part of everyday life. In Denmark, facemasks must be worn on public transport and hands disinfected upon entering the supermarket. Initially, all pregnant women were to be tested for COVID-19, birthing classes were virtual, the first consultation with the midwife was by telephone and partners were not allowed to be present at ultrasound scanning. Today, the restrictions are more lenient. The restrictions were initially introduced although no evidence indicated that expectant mothers were especially susceptible to COVID-19 or vulnerable to severe illness if they became infected.

“When we had the flu epidemic in 2009, some pregnant women became severely ill. So the concern has been that pregnant women might be more susceptible and have more severe illness if they got COVID-19,” says Stine Yde.

Other retroviruses and viruses such as HIV and hepatitis B can be transmitted from mother to child during pregnancy and childbirth. The concern has thus been that COVID-19 could affect the fetus and cause more severe illness among pregnant women and new mothers if they contracted COVID-19.

“However, we knew almost nothing about COVID-19 when it arrived in Denmark. The association between pregnant women and COVID-19 is still only described in sporadic case studies. Some larger studies are beginning to emerge from France and the United States, but otherwise many of the reports of side-effects have come from China with few participants, with the same pregnant women being referred to in several publications. The studies have also been hastily carried out and published and therefore do not outline details on when the baby had actually been infected,” explains Stine Yde.

Stine Yde and her colleagues are conducting an extensive study, and the results look promising so far. None of the newborns in the trial have had COVID-19, and so few mothers had COVID-19 that the exact number cannot be disclosed for legal reasons.

“I think this may indicate several things. Maybe the mothers have taken really good care of themselves and have isolated themselves and the family in the home as much as possible. There has been considerable concern that their partners, for example, would not be allowed to attend the birth if they contracted COVID-19 or that the mothers would be isolated from their child if they got COVID-19. This may be one reason why so few mothers had COVID-19,” says Stine Yde.

Evidence lacking

Evidence suggests that the category of being especially susceptible to COVID-19 in which the health authorities placed the pregnant women has had both advantages and disadvantages for them.

The media have reported a study from Rigshospitalet and Statens Serum Institut in which the number of extremely premature babies declined by 90% when Denmark was most severely locked down. But they have also reported that pregnant women have publicly spoken about their anxiety and stress in connection with the uncertainty of the COVID-19 situation and extreme self-isolation.

In 2013, Stine Yde wrote her PhD dissertation on Q fever, a disease that, like COVID-19, can be transmitted from animals to humans (zoonosis) and is especially prevalent among cattle. When Q fever appeared in Denmark, panic spread. Pregnant veterinarians did not want to go to work because they had read studies that showed that Q fever had resulted in stillbirths, miscarriages and premature babies.

“My dissertation was a major study of pregnant women in Denmark, and some women did have pregnancy complications, but the vast majority had a healthy pregnancy. And that actually meant that we could intervene and change the occupational health recommendations in this area regarding when to stay at home or go to work,” says Stine Yde.

Pregnant women are therefore an important and interesting but also difficult group to investigate, she continues. Researchers must be careful about subjecting this population group to randomized trials, and very strong evidence is needed before dismissing a disease as being a health risk.

“So far, our results do not indicate that pregnant women are an especially susceptible group. There is therefore a risk of inflicting many extra worries on a group that is already pretty worried. But if the authorities’ recommendations are to be changed, this must be done in conjunction with all the other research conducted abroad and in Denmark. And we still lack robust data and more evidence,” explains Stine Yde.

Even though the COVID-19 infection rate has varied in Denmark recently, Stine Yde and her colleagues expect to have 1,000 trial participants and thus finish the project before the end of 2020. They currently lack a few hundred participants, but Stine Yde does not think these will completely change the results.

“It is becoming increasingly clear that the lockdown and isolation caused by COVID-19 have many side-effects. All the fear and limitations for the individual have other costs. When we assess our overall test results and if they continue to be in accordance with what we see in the rest of the world, then as researchers we are also obligated to reassure pregnant women,” concludes Stine Yde.

In April 2020, the Novo Nordisk Foundation awarded a grant to researchers from Aarhus University Hospital and Lillebælt Hospital for the project NOVO COVID-19 Women in Labour and Newborns.

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