The prevalence of a low p-MBL level is higher in patients with unexplained RPL than in the background population, while a high level is significantly less frequent in RPL patients (Nørgaard-Pedersen et al., submitted).~Approximately 50% of RPL patients have none of the evidence-based risk factors associated with RPL. Unexplained RPL is more complicated since finding the cause is essential for offering the optimal intervention to improve the patient's chances of a child.~Other conditions characterized by reproductive failure are infertility and recurrent implantation failure (RIF). The underlying mechanisms and the physiologic stage in early pregnancy being complicated and impeding normal pregnancy may probably differ between these pathologic conditions, since theoretically RIF would involve complicated embryo apposition, adhesion and invasion and clinical/visualized pregnancy losses would involve complicated stages later in the implantation process and fetal development. However, these conditions are suggested to have partly overlapping causes since most of the evidence-based risk factor recur; including parental chromosomal abnormalities, and maternal endocrine disorders, acquired thrombophilia, anatomic abnormalities in the uterine cavity, and endometrial and ovarian diseases. In addition, adverse immune responses against the embryo have been suggested as a cause of reproductive failure. If RPL is associated with a low p-MBL level, RIF may be so too.~The investigators aim to explore the p-MBL level in patients suffering from reproductive failure.~If low p-MBL level is associated with all the investigated subgroups of patients suffering from reproductive failure, this would strengthen our theory that MBL is involved in the pathophysiology characterized by reproductive failure in the very early stages of pregnancy and should therefore take part in the exploration of all patients with reproductive failure.
A low plasma level of mannose binding lectin (p-MBL) is associated with unexplained recurrent pregnancy loss (RPL), but it is not investigated if it is associated with unexplained reproductive failure in general, including recurrent implantation failure (RIF) after assisted reproductive technology (ART) (including IVF, ICSI and FET), recurrent pregnancy loss (RPL) after spontaneous conception, and RPL after ART.