A third of women who die as a result of pregnancy or childbirth are obese, a three-yearly review of maternal deaths revealed yesterday. In some cases caesarean sections had to be performed on beds because mothers were too big for operating tables.

The emergence of obesity as a serious risk factor at birth reflects its rising prevalence in the population as a whole but the 35% figure is half as much again as the 23% of women of childbearing age believed to be obese. Researchers for Why Mothers Die, the latest review from a confidential inquiry into maternal deaths which has reported every three years since the 1950s, were also concerned by high numbers of women who committed suicide or died from other psychiatric causes in late pregnancy or after giving birth.

Many of these deliberately chose violent deaths. They were typically slightly older white professional women with children. Generally women who lived in families where both partners were unemployed were up to 20 times more likely to die than women from more affluent groups.

Women from non white ethnic groups were three times more likely to die, with black Africans including asylum seekers and newly arrived refugees, having a mortality rate seven times higher.

Many who died booked into clinics late or were poor attenders. Although deaths are far lower than half a century ago, researchers are concerned by the fact that the rate of 13.1 deaths per 100,000 maternity cases has not fallen since the last three-yearly check. Some earlier recommendations are being taken up by the government, including asking pregnant women whether they have been victims of domestic violence.