Mother on side better for baby

The research isn't at a point where national guidelines can be issued. Photo / Getty Images

Sleep research yields important new finding.

Babies are more active in the uterus when a pregnant mother lies on her left side than on her back, according to important new research by the University of Auckland.

Professor Peter Stone and colleagues conducted an experiment measuring fetal heart rate as a marker of activity, after an earlier study at the university suggested sleeping on the left side was associated with a lower risk of stillbirth than sleeping on the back or right side.

In the experiment, 29 healthy women in late pregnancy were monitored lying in various positions while awake in a laboratory and again sleeping at home. The fetus' heart rate was monitored via a transducer strapped to the mother.

Professor Stone gave results to the conference of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists in Wellington yesterday.

"During awake studies fetuses were significantly more likely to be in [the active awake state] when the mother was in a left lateral position - 45 per cent of the time - than supine [lying on her back], 12 per cent."

He said it was a new finding and an important piece of evidence to add to the earlier research, an observational study based on interviews with one group of women who had suffered a stillbirth at 28 weeks or later and another group who carried their babies to full term.

The hypothesis being explored is that in the same way that a group of factors - including genetic predisposition and maternal smoking - contribute to sudden infant death syndrome, a related group of factors may cause late-term stillbirths.

"Maybe if you have a mother who has high blood pressure, maybe a genetic predisposition, maybe the baby is not well grown - maybe that baby is on a knife edge. And with a period of time [with the mother] flat on her back you tilt the baby over the balance."

The research isn't at a point where national guidelines can be issued.

"[But] ... if I was managing someone with a growth-restricted fetus or high blood pressure, I would suggest it's advantageous to lie on the left or right side, not flat on the back."

In his study the findings for lying on the left and right were similar.

Fetus activity levels

• Awake 45% of the time when mother lying on left side

• Awake 12.5% of the time when mother lying on back