Repeated miscarriages and hormone treatment for infertility may make pregnant women prone to pre-eclampsia, according to a new study from the Norwegian Institute of Public Health.
The study involved over 20,000 first-time mothers from the Norwegian Mother and Child Cohort Study (MoBa).
It was found that first-time mothers, who had not miscarried or had problems becoming pregnant, had a 5.2 per cent risk of pre-eclampsia.
The researchers also observed that women who had three or more miscarriages had a 50 per cent increased risk of pre-eclampsia, compared with women who had not miscarried.
Women who had one or two miscarriages are not thought to be at higher risk, and those who had both miscarriages and treatment for infertility were at a 13 per cent risk of pre-eclampsia.
The research also showed that women who had infertility treatment had a 25 per cent higher risk of pre-eclampsia, and that those who became pregnant after hormone treatment to stimulate ovulation had a doubled risk of pre-eclampsia compared to women without treatment.
According to the researchers, assisted conception treatment was not linked to an increased risk, even though hormone stimulation is part of the procedure.
Published in the British Journal of Obstetrics and Gynaecology (BJOG), the study report said that though the causes of pre-eclampsia were unknown, the placenta was involved.
The researchers pointed out that the placenta is important for normal development of the pregnancy, and that failure in its development and function seemed to be an important mechanism in the development of pre-eclampsia.
Given that the protective effect seen after earlier normal pregnancies was not present among women with repeated miscarriages, the researchers believe that common causal factors linked to the placenta's development and function might be present in infertility, repeated miscarriages and pre-eclampsia.