Even mild COVID-19 during pregnancy leads to increased likelihood of preterm birth

A large Canadian study confirms that SARS-CoV-2 infection during pregnancy leads to greater hospitalization, adverse maternal outcomes and preterm births. But non-white populations are hit harder. A population surveillance study investigating SARS-CoV-2–affected pregnancies tells what the story is like across Canada. Results were published in JAMA. While other studies show increased risk to maternal and fetal outcomes, reports have varied in terms of the degree of illness severity resulting from SARS-CoV-2 infection, as well as the degree and nature of associated adverse pregnancy outcomes. This study stands out because, “It’s the first national, Canadian, peer-reviewed publication on COVID-19 during pregnancy. It’s important to understand the situation in Canada and bring these data to the international stage to contribute to our global understanding of this topic as well,” said Dr. Elisabeth McClymont, PhD, a post-doc fellow at the Women’s Health Research Institute at the University of British Columbia. Read: The tiniest babies: Shifting the boundary of life earlier The study was conducted using data from the Canadian Surveillance of COVID-19 in Pregnancy (CANCOVID-Preg). It is the only national surveillance program for SARS-CoV-2–affected pregnancies in the country. The purpose of the program “was to contribute to the understanding of SARS-CoV-2 in pregnancy both in Canada and internationally, and so we could have Canadian-specific data to support national and provincial public health policy. Notifications for cases of PCR-tested laboratory-confirmed cases of SARS-CoV-2–affected pregnancy from participating provinces were submitted to the CANCOVID-Preg surveillance team. Data were attained from six provinces from the start of March 2020, to the end of October 2021. During that time period there were 8,786 SARS-CoV-2–affected pregnancies reported in Canada. Of these, 6,012 completed pregnancies were included in the analyses. The researchers noted that all of the cases were from before the Omicron variant arrived. A total of 638 cases were individuals in British Columbia, 2,651 in Alberta, 312 in Manitoba, 529 in Quebec, 1,874 in Ontario, and 8 in Nova Scotia. Subjects had a mean age of 31 years, with 2,381 (39.7%) aged 30 to 35 years. The largest portion of the cohort was white, 767 (37%), followed by 374 (18.4%) South Asian; 245 (12.1%) African, Black, or Caribbean; 240 (11.8%) other (including Indigenous); 169 (8.3%) and East or South East Asian. Alberta numbers were higher partially due to a high number of cases in Alberta as well as the fact that Alberta was very comprehensive in data collection. However, “we don’t believe that this is scientifically valid to highlight,” said Dr. McClymont. The proportion of African, Black, or Caribbean pregnant SARS-CoV-2–positive individuals was 12.1% even though they comprised only 2.2% of Canadian women aged 15 to 49 years. A similar pattern was seen for East or South East Asian, South Asian, and other pregnant SARS-CoV-2–positive individuals, the study said. Most SARS-CoV-2 infections were diagnosed at 28 to 37 weeks’ gestation, 2,148 (35.7%) cases. As for the presence of pre-existing risk factors, 149 (3.4%) had preexisting hypertension, 108 (2.6%) had type 1 or 2 diabetes, and 656 (24.3%) had a BMI greater than or equal to 30. Information relating to which COVID symptoms patients had was available for 4,972 of the cases. Of these, 850 (17.1%) were asymptomatic, while cough and fever were the most common symptoms recorded. Of the 6,012 pregnancies, 466 (7.75%) were hospitalized, 207 (3.4%) required oxygen therapy, and 121 (2.01%) were admitted to ICU. When compared to 9,196 non-pregnant women aged 20 to 49 years in Canada diagnosed with SARS-CoV-2, those who had SARS-CoV-2 during pregnancy were at significantly increased risk of hospitalization: 7.75% compared to 2.93%, and were much more likely to be admitted to the ICU. Details for women outside the study cohort came from national discharge abstract database data from CIHI. As for perinatal outcomes, the rates of preeclampsia, Cesarean delivery and stillbirth were similar between patients with or without COVID-19. However, those with SARS-CoV-2 were more likely to undergo preterm birth (delivery before 37 weeks’ gestation) than those not infected with the virus: 11.1% versus 6.8%. The study noted that: “Preterm birth occurred at an elevated rate, even in cases of mild disease not requiring hospitalization (9.3%).” It was also found that none of the patients who had received at least two doses of any of the SARS-CoV-2 vaccines available in Canada experienced any of the adverse maternal outcomes, adding to the message that the vaccines are important for pregnant people. Dr. McClymont added that “it’s important to note that preterm birth can be a very serious outcome for the infant and can lead to lifelong health impacts.” Doctors should help ensure “that pregnant people are aware of these increased risks so that they can make informed choices about vaccination and other preventive measures,” she said. “This is a well-done study that is very valuable in helping us to better understand whether pregnancy makes a woman more vulnerable to serious complications from SARS-CoV-2 infection,” said Jennifer A Hutcheon, PhD, associate professor of obstetrics and gynecology at the University of British Columbia. She not involved in the study. Whether the increased rates of hospital and ICU admissions seen in the study in pregnant individuals was due to increased caution on the part of physicians, or an increased vulnerability associated with pregnancy, “these events are still very important in-and-of themselves. Hospital and ICU admissions have implications for health services planning, and, for ICU admission in particular, may mean that a pregnant individual needs to be transferred from their home community to receive care, which can be very challenging for families,” she said For physicians, the findings are useful for helping pregnant patients (or those considering pregnancy) to understand the potential consequences of SARS-CoV-2, and the importance of taking steps to reduce their chance of infection.

Even mild COVID-19 during pregnancy leads to increased likelihood of preterm birth

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