A new method of plotting the growth of twins in the womb, developed in the UK, could save thousands of babies from premature delivery or death.
The system involves ultrasound scans and special growth charts that show whether the unborn infants are increasing size at a healthy rate.
Previously doctors had to rely on growth charts designed for single babies, not twins, leading to errors and unnecessary early deliveries.
Twin boys born at London's St George's Hospital on Thursday were the first in the world to have their progress assessed using the new charts.
Kiaan and Kush weighed in at 2kg and 2.1kg respectively after their mother, Mala Vast Dhuri, gave birth by caesarean section.
Dr Asma Khalil, who delivered the twins, also led the St George's team that developed the charts from thousands of measurements of twins growing in the womb.
She said: "The growth charts help us to identify the difference between babies which are truly small because they not developing properly versus twins who are normally small."
Basing decisions about twins on singleton growth charts has in the past led to serious problems being missed, or incorrect diagnoses of growth defects resulting in premature deliveries. In some cases this has resulted in death.
Dr Khalil added: "For us to deliver early when there isn't a reason can result in causing potential harm to the babies. We know that prematurity is associated with the risk of disability.
"The benefits of the twin growth charts would be to reduce the number of babies needing neonatal care after birth. About 50% of multiple birth babies need some form of special unit treatment once they're born but with these new twin growth charts we're hoping to reduce that statistic considerably.
"Of course, our primary objective is to improve healthcare provided for twin babies during pregnancy. We hope the twin pregnancy growth charts will further improve the care for multiple birth women."
The £25,000 research project to develop the charts was made possible by a massive fund-raising appeal organised by the Twins and Multiple Births Association (Tamba).
Keith Reed, the charity's chief executive, said: "This is an extremely important day for foetal medicine. Mala was the first mum to have her twin babies measured using the twin pregnancy growth charts. We hope these charts help many more twin babies to thrive."
Mala, 37, who lives in London and is married to Kiran Dhuri, 42, said: "I'm over the moon to finally meet my gorgeous little boys, thanks so much to the St George's team for ensuring the safe arrival of my babies."