Performing surgery on a baby while they're still in the womb is the best way of treating a common form of spina bifida, researchers have found.

However, there are some potentially dangerous side effects for the mother as it increases the risk of a premature birth and also increases the risk of a ruptured uterus.

Spina bifida is a birth defect that affects the spine and nervous system. One form, called myelomeningocele, affects about 1 baby in 1,000. It means the bones in the back don't form properly, so the spinal cord is exposed and bulges out of the child's back.

Many children with myelomeningocele also suffer from extra fluid that collects in their brain - a condition known as hydrocephalus. To drain the fluid, a tube (called a shunt) often needs to be fitted. This tube is usually there for life.

Before the 1970s, most babies born with spina bifida died before they were 1 year old, but modern treatments mean that most children with the condition now survive to become adults. Most children with myelomeningocele will need lifelong treatment.

To prevent further damage to a child's nervous system, surgery can be used to repair the baby's spine. This is done either soon after birth or while they're still in the womb. It's been impossible to say which approach works best, as until now there's been no good research comparing the two types of surgery. A new study has aimed to settle the question.

The study found that surgery in the womb - known as fetal surgery - worked better than surgery shortly after birth. Far fewer children who'd been operated on before birth ended up needing a shunt to drain fluid from their brain.

The study looked at 158 mothers and their children. Half the babies were operated on in the womb, and the others were treated shortly after birth. Mothers and babies were followed up afterwards so the researchers could check on their health.

Of the babies who'd been operated on after birth, 82 in 100 needed a to have a shunt fitted. This fell to just 40 in 100 where children had been operated on before birth.

At 30 months, children who'd been operated on in the womb were less disabled than children who'd been treated after birth. For example, just 21 in 100 children who'd been treated after birth could walk unaided, compared with 42 in 100 who'd been treated before birth.

Surgery in the womb does have some disadvantages for both mother and baby. It increases the risk of a premature birth. About 69 in 100 babies in the fetal surgery group were born at 36 weeks or sooner, compared with just 15 in 100 babies who had surgery after they were born.

If the baby has surgery after birth, the risks to the mother during childbirth are no higher than usual. But after fetal surgery, women were more likely to have a ruptured uterus. This is a dangerous complication, and can be fatal. Fortunately though, none of the mothers from either group died during the study. Fetal surgery also puts women at risk of a ruptured uterus during future pregnancies, meaning that all future births will have to be by caesarean section.

Among the babies who'd had surgery in the womb, one was stillborn and one died after being born prematurely.Two babies died in the group who'd had surgery after birth, both because of a birth defect affecting their brain.

This was a good-quality study where people were randomly split between two treatments. These studies are the most reliable way of finding out whether a treatment works. Surgery in the womb seemed so much better that the researchers stopped their study early, although that means we only have information on 158 births, instead of the planned 200.

The results of surgery depend a lot on the skill of the surgeon. The study may not apply to hospitals where there's less experience of fetal surgery. The women in the study had been carefully chosen too. For example, obese women were excluded, as surgery would have been more difficult. So, the benefits for a typical woman might not be as big as they were for the carefully selected women in the study.

1.Adzick NS, Thom EA, Spong CY, et al. A randomized trial of prenatal versus postnatal repair of myelomeningocele. New England Journal of Medicine. Published online 9 February 2011.

Posted by Penny Hosie on 14.2.11

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