Thousands of babies in England are being born prematurely, smaller than expected or stillborn because of “alarming” and “devastating” socioeconomic and racial inequality across the country, a landmark study has suggested.

Both are known risk factors for poor pregnancy outcomes. However, until now, little has been known about the scale of their “heartbreaking” impact on women and babies.

Now research involving more than 1m births suggests socioeconomic inequalities account for a quarter of all stillbirths, a fifth of preterm births, and a third of cases of foetal growth restriction (FGR), a condition in which babies are smaller than expected for their gestational age.

At the same time, one in 10 stillbirths and almost one in five FGR cases are due to racial inequalities, the study suggests. The findings, which have prompted calls for urgent action, were published in the medical journal the Lancet.

Dr Jennifer Jardine of the Royal College of Obstetrics and Gynaecologists (RCOG), one of the study’s co-lead authors, said: “I think that people will be shocked. The stark reality is that across England, women’s socioeconomic and ethnic background are still strongly related to their likelihood of experiencing serious adverse outcomes for their baby.”

The review, which was conducted by a team from the National Maternity and Perinatal Audit, analysed 1,155,981 birth records between April 2015 and March 2017 in NHS hospitals in England.

The analysis estimates that 24% of stillbirths, 19% of preterm births, and 31% of FGR cases were attributed to socioeconomic inequality and would not have occurred if all women had the same risk of adverse pregnancy outcomes as women in the least-deprived group.

Adjusting for ethnicity, maternal smoking and body mass index (BMI) substantially reduced these inequalities. That suggests that these characteristics can explain a considerable part of the socioeconomic inequalities in pregnancy outcomes.

Pregnancy complications disproportionately affected Black and minority-ethnic women: 12% of all stillbirths, 1% of preterm births, and 17% of FGR cases were attributed to ethnic inequality.

Prof Jan van der Meulen of the London School of Hygiene & Tropical Medicine, another co-lead author, told the Guardian the disparities were unacceptable but said there were no quick fixes that could immediately solve the problem.

The NHS has set a target of halving stillbirth and neonatal death rates and reducing levels of preterm birth by 25% by 2025.

However, the study findings suggest that current national programmes to make pregnancy safer, which focus on an individual woman’s risk and behaviour and their antenatal care, will not be enough to improve outcomes for babies born in England.

To reduce disparities in birth outcomes at a national level, Van der Meulen said, politicians, public health professionals and healthcare providers must work together to tackle racism and discrimination and improve women’s social circumstances, social support and health throughout their lives.

“National targets to make pregnancy safer will only be achieved if there is a concerted effort by midwives, obstetricians, public health professionals and politicians to tackle the broader socioeconomic and ethnic inequalities,” he said.

The largest increases in excess risk of complications among the most socioeconomically disadvantaged Black and south Asian and women.

Half of stillbirths (53.5%) and seven in 10 FGR cases (71.7%) among south Asian women living in the most deprived fifth of neighbourhoods in England could be avoidable if they had the same risks as white women in the most affluent fifth, the study suggests.

This was similarly the case for nearly two-thirds of stillbirths (63.7%) and half of FGR cases (55%) among Black women from the most deprived neighbourhoods.

“There are many possible reasons for these disparities,” said Van der Meulen. “Women from deprived neighbourhoods and Black and minority ethnic groups may be at a disadvantage because of their environment, for example, because of pollution, poor housing, social isolation, limited access to maternity and health care, insecure employment, poor working conditions, and stressful life events.”

Dr Edward Morris, the president of the RCOG, said the findings of the study were alarming, adding: “They provide more evidence that poverty, racism and discrimination can affect women throughout their lives and ultimately lead to devastating incidences of pregnancy complications and baby loss.”

Dr Christine Ekechi, a consultant obstetrician and gynaecologist and co-chair of RCOG’s race equality taskforce, said the disparities were heartbreaking.

“These women are being let down by a healthcare system that is supposed to protect them. Reducing the occurrence of potentially avoidable adverse pregnancy outcomes needs to be a national priority,” she said.