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Published on 29 March 2024 in the journal Nature, the study examines the risk factors associated with placenta accreta* after vaginal delivery. Until now, this complication of pregnancy has been seen, in the majority of cases, in women who have had another complication of pregnancy, placenta previa. However, the study showed that more than half the cases of placenta accreta occurred in women with no previous history of placenta previa or caesarean section. But these women had had recourse to artificial procreation.
Carried out between 2007 and 2020, the study was based on data from Japan's national artificial procreation register, managed by the Japanese Society of Obstetrics and Gynaecology. To avoid any effect of uterine scarring on the risk of placenta accreta, only cases of vaginal delivery were included, representing 224,043 live-born singletons after embryo transfer. Of the 1,412 cases of placenta accreta, 1,360 (96.3%) concerned cycles in which the embryos had been frozen (compared with 3.7% when the embryos transferred were fresh).
Other risk factors have been identified for each of these categories. For cycles using fresh embryos, the assisted hatching technique* and embryo transfer at the blastocyst stage (5 to 6 days after fertilisation) would increase the risk of placenta accreta. For cycles based on frozen embryos, the risk of placenta accreta increases significantly when the woman's cycle has been artificially programmed, requiring a large dose of hormones to prepare the endometrium to receive the embryo. This represents the highest risk of placenta accreta, accounting for 1.4% of cases.
This new risk must be added to the list of known risks, including ovarian hyperstimulation, premature delivery, a higher prevalence of congenital anomalies and a greater risk of pre-eclampsia. Alternatives to artificial procreation, such as NaProTechnologies, should be better known so that couples can have a chance to procreate without the risks involved in artificial procreation.
*Placenta accreta spectrum (PAS) is a life-threatening complication of pregnancy that can lead to significant blood loss during childbirth. This condition results from an abnormal invasion of the placenta into the myometrium of the uterine wall. Usually, the main risk factor for PAS is scarring of the uterus from previous uterine surgery such as caesarean section.
*Assisted hatching involves opening a small hole in the blanket (zona pellucida) surrounding the embryo to encourage it to emerge and implant in the woman's uterus.