Health services at one of New Zealand's largest maternity providers are under the spotlight after it was found to have a death rate significantly above the national average.

The death rate in the Counties Manukau District Health Board area for newborns and fetuses from mid-pregnancy was about 13 in 1000 births in 2007. The national average was just over 10.

Counties, which has the greatest number of births in the country, is the only health district to unequivocally exceed the average. Several others, including Northland, may also be above the average, but because they have far fewer births the statistical calculations are uncertain.

Counties' outlier status was identified by the perinatal and maternal mortality review committee. Its chairwoman, obstetrics and gynaecology professor Cindy Farquhar, said they were of concern.

She said it was imperative women book their maternity care early, ideally before the 10-week point in pregnancy, and she wants a national advertising campaign to promote this.

The committee has urged further investigation at Counties, which is being done by the DHB.

"Perinatal-related mortality" covers the last half of pregnancy, including abortions and stillbirths, and newborns up to 28 days old.

The DHB says investigations suggest its above-average rate is associated with matters such as the high rate of deprivation in its population, its high rate of obesity, large families and a tendency for some women to seek maternity care only after medical problems have begun.

Its clinical director of women's health, Dr Keith Allenby, said it appeared the kind of care provided was not a factor - the rate was the same in different care models involving midwives or combinations of midwives and GPs or obstetricians.

The DHB's list of "sentinel" events for 2007/8 includes the death of a baby from brain damage caused by a lack of oxygen during delivery.

This followed a "failure to recognise and act on deteriorating fetal heart trace during labour" and was linked to an inadequate hand-over of the patient to Middlemore Hospital from a satellite birthing unit.

In 2006, the Herald reported on the death of newborn Tyla Phillips at Middlemore in 2005, a case in which the hospital criticised delays from misreading of the fetal heart-rate monitor and unnecessary blood tests.

Counties has for years struggled with a critical shortage of midwives, the main providers of maternity care.

It has tried to address this partly by paying GPs to take a greater maternity role than elsewhere in a form of shared care.

A Health Ministry paper obtained by the Weekend Herald shows the DHB, in a submission on the now-discontinued Maternity Action Plan, suggested that "its model of care allows it to achieve excellent outcomes", including one of the country's lowest rates of obstetric intervention.

But the paper contrasts this with the Farquhar committee's findings, and says the committee will continue to closely monitor the DHB's rates.

It notes that shared care means there is often little continuity of maternity care.

Having a single person, usually a midwife and a colleague, take responsibility is considered a virtue of the lead maternity carer system.

Counties wants to encourage the creation of clinical networks of GPs and midwives and make primary health organisations the hub of community maternity care.