A team of scientists have identified three genes responsible for molar pregnancy, a complication that ends in miscarriage, and is prone to repetition once it has occurred.

“Our findings add three new genes to the list of mutations leading to fetal loss and will allow for more DNA testing for patients in order to prevent the recurrence of molar pregnancies and provide better genetic counselling and management for couples,” says Rima Slim, PhD, a researcher in the child health and human development program at the Research Institute of the McGill University Health Centre. Slim, an associate professor of human genetics and obstetrics and gynecology at the University, led the study, which included women from Canada, India, Turkey and the US.

A molar pregnancy, also known as hydatidiform mole (HM or h mole), occurs when the active genetic material of a fertilized egg is composed entirely of the father’s DNA. In a typical fertilized egg, half of the genetic material is from the father, and half from the mother; in a molar pregnancy, the mother’s DNA is erased or deactivated from the egg, while the father’s DNA is duplicated. US estimates put the likelihood of a molar pregnancy at 1 in 1,000 pregnancies. While there are no reliable stats for India, some evidence suggests molar pregnancy is much more common among South Asian women. Maternal age — younger than 20 or older than 35 — increases chances of a molar pregnancy, as does having had one molar pregnancy already.

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There are two versions of molar pregnancy: complete and partial. In a complete molar pregnancy, an egg that lacks genetic material is fertilized by a sperm. Despite the name, this does not result in a pregnancy, as no embryo is formed. It does, however, generate abnormal placental growth, as the body is tricked into thinking its pregnant. In a partial molar pregnancy, two sperm fertilize one egg that does contain genetic material, resulting in miscarriage of an unviable embryo that contains too much DNA — 69 chromosomes instead of the typical 48 — and abnormal placental growth.

The abnormal placental growth can continue, even after pregnancy loss, and can, if untreated, cause serious complications, including a rare form of cancer.

“The painful experience of a fetal loss associated with the discovery of an abnormal pregnancy is often destabilizing and stressful for women,” says Magali Breguet, nurse coordinator of the Quebec Trophoblastic Disease Network, a collaborator in the study. “This collaboration is a positive step forward for women who must undergo several months of medical monitoring and also live with the anxiety that their next pregnancy may also be a molar pregnancy.”