Scientists have grown “mini placentas” in a breakthrough that could transform research into the underlying causes of miscarriage, stillbirth and other pregnancy disorders.

The tiny organoids mimic the placenta in the early stages of the first trimester and will be used to understand how the tissue develops in healthy pregnancies, and what goes wrong when it fails.

The mini placentas are so much like the real thing they can fool over-the-counter pregnancy tests. “If we put a pregnancy stick into the medium from the organoids it reads‘pregnant’,” said Ashley Moffett, a senior researcher on the team and professor of reproductive immunology at Cambridge University.

In a healthy pregnancy the placenta grows and attaches to the wall of the womb where it provides oxygen and nutrients for the baby, while removing waste from the foetus blood. It also secretes hormones into the mother.

Pregnancies can fail when the embryo does not implant properly in the womb and the placenta does not attach as it should. Understanding what goes wrong in these cases has been hard to investigate because scientists do not have placentas to study, and the placentas of other animals are too different to make meaningful comparisons.

“We can now begin to do experiments on how placental development occurs in the uterine environment,” said Moffett.

The Cambridge team grew the organoids in their laboratory using cells from frond-like structures called villi which are found in placental tissue. The cells organised themselves into multi-cellular structures capable of secreting the proteins and hormones that affect the metabolism of the mother during pregnancy.

The organoids range in size from a tenth of a millimetre to half a millimetre. They can be frozen and stored and then thawed out when needed.

Researchers want to use the organoids to study some of the most common pregnancy disorders, such as pre-eclampsia, stillbirth and growth restriction. But the lab grown mini-placentas will also help scientists understand how certain infections affect unborn babies.

Outbreaks of Zika virus have been linked to abnormal brain development in babies born to women with the infection, but it is not clear how the virus crosses the placenta when the very similar dengue virus does not.

Other work will investigate the hormones and proteins secreted by the organoids as they grow, with a view to identifying substances that could provide an early warning that the placenta is not working properly. “These women could be followed more closely,” said Moffett. Details of the research are published in Nature.

Margherita Turco, lead author of the research, said: “The placenta is absolutely essential for supporting the baby as it grows inside the mother. When it doesn’t function properly it can result in serious problems, from pre-eclampsia to miscarriage, with immediate and lifelong consequences for both mother and child.”

The mini-placentas could also be used to check the safety of new drugs taken during early pregnancy, and shed light on how chromosomal abnormalities can upset a baby’s normal development. Further on the placentas could provide stem-cell therapies for failing pregnancies, the researchers said.