Citat taget ur en forskningsartikel review:
"Bleeding
A possible result of the unique, non-physiological immunologic relationship between the fertilized oocyte and the maternal decidua is shallower placental invasion (Dekker et al., 1998; Moffett and Loke, 2006). The higher incidence of bleeding complications in the first trimester could be related to this insufficient placentation. On the other hand, excessive invasion might result in more post-partum haemorrhage in ED pregnancies as a result of placenta praevia or abnormal placentation (Sheffer-Mimouni et al., 2002).
The incidence of first trimester vaginal bleeding is increased in ED pregnancies, ranging from 12 to 53% of cases (Pados et al., 1994; Abdalla et al., 1998; Soderstrom-Anttila et al., 1998a, b). Significant blood loss is estimated to occur in 43?53% of first trimester cases (Soderstrom-Anttila et al., 1998a, b; Sheffer-Mimouni et al., 2002) and 6% of second trimester cases (Pados et al., 1994; Sheffer-Mimouni et al., 2002). The incidence of first trimester bleeding is substantially higher if compared with standard IVF pregnancies (Soderstrom-Anttila et al., 1998a, b) and second trimester bleeding is higher if compared with the spontaneously conceived population (<1%) (Lipitz et al., 1991). It has been assumed that more bleeding complications are associated with multiple implantation sites and early fetal loss (Shaw and Sauer, 1995). However, in ED cases in which only two oocytes per cycle are transferred, the frequency of bleeding still remains high (Soderstrom-Anttila et al., 1998a, b). Other explanations, such as endometrial preparation therapy, have been suggested, but a possible relationship between various steroid replacement regimens and first trimester bleeding is difficult to assess."
I första trimestern är inte vår kropp självständigt gravid- försörjer sig inte komplett hormonellt. Kort och gott.