Study finds no evidence of intrauterine vertical transmission of COVID-19 infection

There is currently no evidence that the 2019 novel coronavirus disease (COVID-19) causes severe adverse outcomes in neonates or that it can pass to the child while in the womb, according to a small observational study of women from Wuhan, China, who were in the third trimester of pregnancy and had pneumonia caused by COVID-19.

In the study, published in The Lancet, there were two cases of fetal distress, but all nine pregnancies resulted in livebirths. The study also finds that symptoms from COVID-19 infection in pregnant women were similar to those reported in non-pregnant adults, and no women in the study developed severe pneumonia or died.

The authors of the new study caution that their findings are based on a limited number of cases, over a short period of time, and only included women who were late in their pregnancy and gave birth by cesarean section. The effects of mothers being infected with the virus during the first or second trimester of pregnancy and the subsequent outcomes for their offspring remain unclear, as well as whether the virus can be passed from mother to child during vaginal birth.

The new study comes after the news of a newborn (born to a mother infected with COVID-19) testing positive for COVID-19 infection within 36 hours of birth, which prompted questions about whether the virus could be contracted in the womb.

Talking about this case, lead author of the study Professor Yuanzhen Zhang, Zhongnan Hospital of Wuhan University, China, says: "It is important to note that many important clinical details of this case are missing, and for this reason, we cannot conclude from this one case whether intrauterine infection is possible. Nonetheless, we should continue to pay special attentions to newborns born to mothers with COVID-19 pneumonia to help prevent infections in this group."

Co-author, Prof Huixia Yang, Peking University First Hospital, China, adds:

Existing studies into the effects of COVID-19 apply to the general population, and there is limited information about the virus in pregnant women. This is important to study because pregnant women can be particularly susceptible to respiratory pathogens and severe pneumonia, because they are immunocompromised and because of pregnancy-related physiological changes which could leave them at higher risk of poor outcomes. Although in our study no patients developed severe pneumonia or died of their infection, we need to continue to study the virus to understand the effects in a larger group of pregnant women."

In the study, the medical records of nine pregnant women who had pneumonia caused by COVID-19 infection were retrospectively reviewed. Infection was lab-confirmed for all women in the study, and the authors studied the nine women's symptoms.

In addition, samples of amniotic fluid, cord blood, neonatal throat swabs and breast milk were taken for six of the nine cases and tested for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Importantly, the samples of amniotic fluid, cord blood, and neonatal throat swabs were collected in the operating room at the time of birth to guarantee that samples were not contaminated and best represented intrauterine conditions.

All mothers in the study were aged between 26-40 years. None of them had underlying health conditions, but one developed gestational hypertension from week 27 of her pregnancy, and another developed pre-eclampsia at week 31. Both patients' conditions were stable during pregnancy.

The nine women in the study had typical symptoms of COVID-19 infection, and were given oxygen support and antibiotics. Six of the women were also given antiviral therapy.

All nine pregnancies resulted in livebirths, and there were no cases of neonatal asphyxia. Four women had pregnancy complications (two had fetal distress and two had premature rupture of membrane), and four women had preterm labour which was not related to their infection and occurred after 36 gestational weeks. Two of the prematurely born newborns had a low birthweight.

The authors note that their findings are similar to observations of the severe acute respiratory syndrome (SARS) virus in pregnant women, where there was no evidence of the virus being passed from mother to child during pregnancy or birth.

They also explain that future follow-up of the women and children in the study will be necessary to determine their long-term safety and health.

They note some limitations in their study, including that the risk of infection in pregnant women and the effects of the time or mode of delivery on pregnancy outcomes were not evaluated. They say that future research is needed to determine whether COVID-19 could damage the placenta as this could increase risk of vertical transmission.

Writing in a linked Comment, Dr Jie Qiao (who was not involved in the study), Peking University Third Hospital, China, notes that this new research helps to understand the clinical characteristics, pregnancy outcomes, and vertical transmission potential of COVID-19, and notes that this is valuable for preventive and clinical practice in China and elsewhere under such emergent circumstances.

She also compares the effects of the virus to those of SARS, and says:

Previous studies have shown that SARS during pregnancy is associated with a high incidence of adverse maternal and neonatal complications, such as spontaneous miscarriage, preterm delivery, intrauterine growth restriction, application of endotracheal intubation, admission to the intensive care unit, renal failure, and disseminated intravascular coagulopathy. However, pregnant women with COVID-19 infection in the present study had fewer adverse maternal and neonatal complications and outcomes than would be anticipated for those with SARS-CoV-1 infection. Although a small number of cases was analyzed and the findings should be interpreted with caution, the findings are mostly consistent with the clinical analysis done by Zhu and colleagues of ten neonates born to mothers with COVID-19 pneumonia."