Routine use of unnecessary interventions, including Caesarean section, cutting to facilitate childbirth and restrictions on movement during labour, can have lasting effects on mothers and babies.
According to a series of papers in The Lancet journal, the risks exist in both poorer parts of the world and in high-income countries such as the UK
The researchers say increasing the number of independent midwife units would halve the number of maternal deaths while also reducing unnecessary controversial medical interventions.
Caesarean sections in Scotland have been increasing steadily, to more than one quarter (27.8 per cent) of births in for the year to March 2012. It means more than 16,000 babies were born by C-section in that year.
The papers' authors say that "over-medicalisation" has become an issue, not just for high-income nations but also more deprived countries, which also suffer from a lack of effective midwifery.
Professor Caroline Homer, one of the researchers from the University of Technology in Sydney, Australia, said: "Both under-use and over-use of medical interventions in pregnancy contribute to short and long-term illness for an estimated 20 million child-bearing women [worldwide].
"This not only effects their health and wellbeing, but may also result in their needing to pay for ongoing health-care costs, and on the ability of their families to escape poverty."
In high-income countries, midwife-led units in, or next to, hospitals were better at encouraging natural births and lower levels of hormone treatment, assisted birth, Caesarean birth and vaginal cutting than conventional labour wards, evidence showed. There was no difference in infant outcomes between the two.
Independent midwife care also appeared to have important benefits, according to one Danish study, including reduced maternal ill-health and an increased likelihood of spontaneous birth.
Each year, an estimated 139 million births take place around the world, and almost 300,000 women die during pregnancy, say experts. They estimate that if midwifery coverage increased by just one quarter, the current rate of maternal deaths could be halved by 2030.
Professor Mary Renfrew, an author from the School of Nursing and Midwifery at the University of Dundee, said: "Many of the needs of childbearing women, their babies, and families across the world are still not being met, despite long-standing recognition that women and their babies need access to health care which provides more than just emergency interventions for acute medical problems.
"Although midwifery is already widely acknowledged as making a vital and cost-effective contribution to high-quality maternal and newborn care in many countries, its potential social, economic and health benefits are far from being realised on a global scale."
Cathy Warwick, chief executive of the Royal College of Midwives (RCM), said: "This is a vital report not only for countries where a reduction in maternal and neonatal mortality remains a significant challenge, but also for developed and high income countries.
"Most importantly, the authors, having examined what women and babies need, conclude that we will not make enough progress in improving the care of women and babies if we continue to focus on one-off interventions to save lives. Instead, we must offer a package of midwifery care.
"Very importantly, the authors emphasise the need to avoid unnecessary interventions in childbirth, a position the RCM has been advocating and promoting for some time."