Today pregnancy brings a whole battery of tests and scans to check on the baby's development. But what happens when tests reveal that the fetus isn't growing?

There is very little that can be done to treat or prevent what's called fetal growth restriction. So doctors monitor the pregnancy closely in the hope that the fetus will be able to stay in the womb long enough to grow to size where it can survive outside.

Sometimes, it's not safe for the pregnancy to continue - either for the woman, if she becomes gravely ill, or for the fetus if it stops growing entirely.

But what happens when the baby is still so tiny that it's difficult to predict whether it will survive outside the womb or not? And if the baby does survive, he or she may go on to have development disabilities. Is it ethical to try to resuscitate it?

Survivors often spend months in intensive care, where they have to endure invasive painful procedures. When is it ethical to stop keeping them alive?

These dilemmas wouldn't arise for these growth-restricted babies if there was a way to treat or prevent the problem in the womb. But, as Professor Anna David explains, trialling untested medicines in pregnant women is seen as particularly ethically challenging.

It's a challenge that she has taken on. She's involved in two clinical trials in pregnant women to find out if the interventions improve fetal growth in the womb.

Producer: Beth Eastwood

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