COVID-19 and pregnancy
How COVID-19 runs its course in pregnancy, which risks increase, whether the vaccines are safe in pregnancy and when they can be given.
General background
Certain changes in the cardiovascular, respiratory and immune systems during pregnancy make pregnant women more susceptible to infection. Respiratory infections are no more frequent in pregnancy than otherwise, but if illness develops, the physiological changes of this period raise the rate at which its risks appear. An increased heart rate and oxygen consumption, an increase in the transverse diameter of the chest, and reduced lung capacity as the diaphragm rises all lower a pregnant woman's tolerance of low oxygen. Changes in lung volumes and widening of the blood vessels lead to swelling of the mucosa and increased secretions in the airways. In pregnant women with viral pneumonia, premature birth, restricted foetal growth, low birth weight and a five-minute Apgar score below seven are all more frequent than in those without.
Observation and accumulated knowledge through the pandemic showed pregnancy and delivery to be risk factors for severe SARS-CoV-2 infection.
The clinical picture in pregnancy
It can range from mild symptoms — fever, cough, sore throat, muscle aches, fatigue — to severe ones requiring intensive care: pneumonia, acute respiratory distress syndrome, kidney failure and multi-organ failure. Fever, cough and breathlessness occur at a lower rate in pregnant women than in those who are not pregnant. The symptoms of COVID-19 in pregnancy do not differ from those in adults generally. 12.1% may be symptomatic.
Because the maternal immune system is somewhat suppressed in pregnancy, with swelling of the respiratory mucosa, a raised diaphragm and higher oxygen consumption, pregnant women are more prone to respiratory infections. Nevertheless, on the data available, no significant difference in clinical course has been identified in pregnant women compared with the general population. The severity of symptoms in symptomatic cases is similar to that in non-pregnant women. Among pregnant women, 86% had mild disease, 9.3% severe and 4.7% critical (in the non-pregnant COVID-positive population the figures were 80% mild, 15% severe and 5% critical).
Which risks increase
In pregnant women who have had COVID-19, the risk of premature birth, miscarriage, restricted growth and pre-eclampsia all increase. Current studies have also shown a marked increase in admissions to intensive care and in maternal deaths.
Who is at particular risk of more severe illness
Those with an accompanying medical condition such as diabetes or hypertension; those with a history of congenital or acquired heart disease; cancer patients; older mothers; those with serious respiratory disease such as cystic fibrosis or advanced asthma; those with chronic liver or kidney disease; those taking immunosuppressive medication; and those with a congenital metabolic condition such as sickle cell anaemia are all at greater risk than other pregnant women.
Are the vaccines safe in pregnancy?
COVID-19 runs a more severe course in pregnant women than in those who are not pregnant, and results in more deaths; in many countries it became the most frequent cause of maternal death. On review of the data for inactivated and mRNA vaccines in pregnancy, vaccination of pregnant women is recommended. The vaccines can be given before pregnancy and at any stage from its beginning. The World Health Organization recommends that the SARS-CoV-2 vaccines it has approved be given to pregnant women, and the CDC and the American College of Obstetricians and Gynecologists also recommend COVID-19 vaccination for pregnant women, those breastfeeding and those planning a pregnancy.
Inactivated vaccines are effective and have long been used safely in pregnancy.
For the more recently developed mRNA vaccines, a CDC study covering 139,000 pregnant women showed them to be effective in pregnancy, with no serious adverse effect on mother, foetus or newborn. mRNA vaccines contain no live virus and use no adjuvant to increase their effect. The mRNA in the vaccine does not enter the cell nucleus and cannot alter the human genome. In 92,000 pregnant women, the rate of miscarriage was found to be no higher in those vaccinated against COVID-19 than in those unvaccinated.
Data from animal and clinical studies have shown that COVID-19 vaccines, mRNA vaccines in particular, have no harmful effect on mother or baby, that they protect the mother and that they reduce the risk of illness 5- to 10-fold.
When the data of 827 pregnant women in the United States who received an mRNA vaccine and gave birth were examined, the vaccines were found not to have caused any problem — miscarriage, stillbirth, congenital anomaly, effects on the baby's development, premature birth or neonatal death.
In 2,456 pregnant women given an mRNA vaccine immediately before pregnancy or in the first 20 weeks, no increase in the risk of miscarriage was seen.
In another study assessing 424 vaccinated pregnant women, most of them healthcare workers, adverse outcomes were reported at a similar frequency in both mothers and babies as in those who were unvaccinated.
Maternal antibodies have also been shown to cross the placenta and pass into breast milk, providing the newborn with passive immunity against SARS-CoV-2. Vaccination in pregnancy reduces the risk of catching the infection and provides the transfer of protective antibodies into cord blood and breast milk.
Vertical transmission — from mother to baby in the womb
The placenta also carries the ACE2 receptors the virus binds to. Theoretically, then, the placenta could become infected with SARS-CoV-2 and the virus could pass to the foetus and cause infection. On the literature available, however, vertical transmission of SARS-CoV-2 is low. Recent data indicate that vertical transmission to the foetus does not occur: to date the virus has not been found in the cord blood or nasal samples of newborns delivered by COVID-positive mothers, nor in the amniotic fluid or placentas of those mothers. It should not be forgotten, though, that publications on the subject remain few and the numbers of pregnant women in them small, so larger studies are needed.