Infected with COVID-19 during Pregnancy! What are the Effects on the Baby?

The new coronavirus infection (COVID-19) is spreading all over the world, and its effects on pregnant women are also attracting attention, and research reports are gradually accumulating.

Most pregnant women may feel uneasy if they are infected with COVID-19 during pregnancy, therefore we will explain what will happen if you get infected.

COVID-19 Infection during pregnancy

In a study on the effects of COVID-19 on pregnancy, one in six women became severely ill and one in four had a premature birth. The mortality rate was 2%. The risks of severe disease included obesity, smoking history, diabetes, and gestational hypertensive nephropathy.

On the other hand, it has not been very clear how infection with COVID-19 during pregnancy would affect the health of the baby (neonatal prognosis).

This time, based on a paper published in the medical journal JAMA in May 2021, we would like to introduce what we have learned about the effects of the new coronavirus infection in pregnant women on their babies.

The paper analyzed 88,159 newborns born between May 1, 2020, and January 31, 2021, in Sweden. We chose this as our reference because it is one of the largest and most reliable studies reported so far, and the quality of the database is considered to be high.

How many newborns were infected with the coronavirus?

Of the 88,159 newborns (49.0% girls) included in the study, 2323 (1.6% of the total) were delivered by mothers (2286) who were positive for the coronavirus (technically, the mothers were infected somewhere between pregnancy and one week postpartum).

This database covers almost all deliveries in Sweden. In addition, Sweden has been registering all COVID-19 cases since February 2020, so we believe that the figure “1-2% of babies were born to mothers who were positive for the new coronavirus” is somewhat reliable.

In addition, about 0.3% of all deliveries were newborns positive for the new coronavirus.

Looking at the data in Japan, as of July 16, 2021, the cumulative number of infected babies in the birth 0-2 months was 61. However, the figures for newborns alone could not be confirmed.

It is difficult to calculate exactly what percentage of all babies born are infected, but since the above data is from May 2020, we can estimate that it is less than 1% of all deliveries if we consider 14 months. Therefore, it is considered to be about the same or even less than that reported in Sweden.

What was the health status of the babies born to moms infected with COVID-19?

Then, were the babies born to pregnant women who tested positive for the new coronavirus in worse health than those born to women who did not?

In this study, babies born to moms who were positive for the new coronavirus had more complications in several categories.

  • Preterm birth
  • Endotracheal intubation at birth
  • Respiratory distress syndrome
  • Other respiratory diseases
  • Hyperbilirubinemia

In addition, the neonatal mortality rate was not statistically different.

What caused more complications in the newborns?

The important question here is why babies born to moms who were positive for the new coronavirus had more of these complications.

In this study, the mechanism was also examined. And the results showed the following.

  • Preterm birth had the strongest impact on the complications of respiratory diseases in newborns.
  • The direct effect of maternal infection with the new coronavirus itself was unlikely.

In other words, pregnant women who were positive for the new coronavirus had a higher risk of premature birth, and many babies were born prematurely, resulting in a clear increase in neonatal complications such as respiratory diseases.

Conversely, even if a pregnant woman is infected during pregnancy, at least clinically, it is unlikely that the virus in her body will directly affect her baby through the placenta (however, this is based on current information and should be updated based on future research reports).

Above all, it is important to prevent infections during pregnancy.


To summarize this research report and previous studies..

  • Infection with new coronaviruses during pregnancy increases the risk of preterm birth.
  • An increase in preterm births leads to an increase in neonatal complications.
  • The direct negative impact of the virus on newborns seems to be very small.

In other words, we think the most important thing is to “prevent infection during pregnancy and not increase the risk of preterm birth”. Currently, vaccines are the most effective way to prevent and avoid serious infections.

This is the joint view of public institutions and governments in Japan, the United States, the United Kingdom, and other countries.