Urinary tract infections in pregnant women reduce the risk of an unexplained stillbirth, rather than increasing it. This surprising discovery might even lead to ways of preventing some inexplicable stillbirths.
Stillbirths due to unknown causes claim more babies than cot deaths (sudden infant death syndrome), yet very little is known about them. Obesity, smoking, poor education and older age in the mother are known risk factors.
So when Frederik Fr酶en and his colleagues at the University of Oslo in Norway looked at 241 stillbirths and 582 controls, they expected women in poor health or with complications during pregnancy would be at the greatest risk.
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But instead they found that women whose urinary tracts were infected by bacteria during pregnancy were 70 per cent less likely to have an unexplained stillbirth. 鈥淭hat was really quite surprising,鈥� says Fr酶en. 鈥淚f anything, it was the opposite of what we were expecting. It鈥檚 against everything that you can find in any textbook.鈥�
But not everyone is convinced. 鈥淚t is a little simplistic to say that urinary tract infection is protective,鈥� says Ruth Fretts, an expert on unexplained stillbirths at the Harvard Medical School.
Fetal protection
The researchers are not suggesting that this beneficial effect outweighs the other consequences of urinary tract infections, which can restrict fetal growth.
What it does suggest, says Fr酶en, is that the antibodies a mother produces in response to the urinary infection might be protecting the fetus from infection with the same bacteria, which can reaching the uterus through the vagina.
Both kinds of infection can be caused by a mother鈥檚 gut bacteria. So some unexplained stillbirths might be due to low-level bacterial infection in the fetus, undetectable at autopsy.
Brain damage
Other evidence also supports the infection theory. Intrauterine infections have been implicated in fetal brain damage, and could play a role in cot deaths as well.
In 1999, David Drucker of the University of Manchester found that injecting blood from infants who had died of SIDS into chick embryos killed them, suggesting that the blood carried a toxin. But the same blood did not kill the chicks when mixed with antibodies against the suspected toxin.
It is still only a hypothesis, however, says Fr酶en. 鈥淥f course, we cannot suggest that high-risk mothers should be given [antibodies] to protect the fetus based on this study alone.鈥� But he and his colleague have now started looking for bacterial toxins in the amniotic fluid of unexplained stillbirths, as well as for ways to neutralise them.