Three newborns with coronavirus may have got the disease from their mums during pregnancy or childbirth, researchers have said.
A new study looked at 33 babies born to mothers with Covid-19 in China, and found that three of them tested positive for the virus.
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All three babies were delivered by caesarean section, and there were no deaths.
Experts in the UK said it was unlikely the disease was transmitted through the placenta, and possible the newborns were infected shortly after birth instead.
The study published in Jama Paediatrics reported the three newborns, who were born at Wuhan Children’s Hospital between January and February, were clear of Covid-19 in a matter of days after treatment.
The researchers said that because strict infection and prevention controls were implemented during delivery, they could rule out that the babies were infected via vertical maternal-fetal transmission.
This can include transmission before birth, the weeks immediately prior to or after birth, or after birth.
The scientists are from the Children’s Hospital of Fudan University in Shanghai, the Institute of Maternal and Child Health, Wuhan Children’s Hospital, Huazhong University of Science and Technology and the Maternal and Child Health Hospital of Hubei Province.
They wrote: “Because strict infection control and prevention procedures were implemented during the delivery, it is likely that the sources of Sars-CoV-2 in the neonates’ upper respiratory tracts or anuses were maternal in origin.
“Although two recent studies have shown that there were no clinical findings or investigations suggestive of Covid-19 in neonates born to affected mothers, and all samples, including amniotic fluid, cord blood, and breast milk, were negative for Sars-CoV-2, the vertical maternal-fetal transmission cannot be ruled out in the current cohort.”
They added that it was, therefore, crucial to screen pregnant women and implement strict infection control measures, quarantine of infected mothers, and close monitoring of neonates at risk of Covid-19.
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Andrew Shennan, professor of obstetrics at King’s College London, said: “Transmission from mother to baby of coronavirus has not previously been observed.
“Studies have shown that coronavirus has not passed to amniotic fluid, fetal cord blood, placentas or the genital tract of infected mothers.
“These three cases show the babies are at risk of infection, but given when they are positive (two days after delivery) this could still be after delivery.
“We need more evidence to prove transmission from mother to baby can occur in pregnancy.
“Mothers can be reassured that their babies are usually safe even if the mother is infected.”
Andrew Whitelaw, emeritus professor of neonatal medicine at the University of Bristol, added: “As all infants had amniotic fluid and umbilical cord blood tested for Covid-19 with negative results, this is evidence against the virus being transmitted from mother to fetus via the placenta.
“It seems more likely that the three infants were infected very soon after delivery, possibly from the mother’s fingers.
“On the basis of this small but much-needed study, infants born to mothers with Covid-19 do not appear to be at serious increased risk, over and above the background risks of pregnancy and delivery.
“However, strict precautions need to be taken to minimise virus transmission to staff and other patients. Conclusions may have to change when larger numbers of infants are reported.”
Advice for pregnant healthcare workers
It comes as the Royal College of Obstetricians and Gynaecologists released updated advice to pregnant women working in healthcare.
The guidance emphasises that pregnant women of any gestation should be offered the choice of whether to work in direct patient-facing roles during the coronavirus pandemic.
It says that women who are less than 28 weeks pregnant should practise social distancing but can choose to continue working in a patient-facing role, provided the necessary precautions are taken.
Women who are over this stage in pregnancy, or have underlying health conditions, should avoid direct patient contact and are recommended to stay at home, they said.
Dr Jenny Harries, Deputy Chief Medical Officer, said: “The Government has taken the precautionary approach to include all pregnant women in a vulnerable group.
“This guidance will give pregnant healthcare workers the ability to make an informed choice about how they can continue to make an active and valuable contribution to the huge challenge facing us, whether at home or in the workplace.”
Evidence, which has been based on pregnant women who have contracted other similar respiratory viruses, suggests those who contract Covid-19 in the third trimester are more likely to become seriously unwell.
This may also lead to preterm birth of the baby, intended to enable the mother to recover through improving the efficiency of her breathing or ventilation.
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Currently, there is no evidence to suggest that coronavirus causes problems with the baby’s development or causes miscarriage.
There is also no evidence that coronavirus can be passed from mother to baby in utero and no previous coronavirus has been shown to cause fetal abnormalities.
The RCOG says that this guidance is based on limited evidence from the pandemic so far with evidence extrapolated from other similar viral illnesses.