Implantation of the human embryo: clinical and epidemiological aspects.

The aim of this thesis is to define determinants of impaired implantation and adverse pregnancy outcome in a retrospective manner. Our results demonstrate that pregnancy outcome in singletons of older mothers (> or = 35 years) is less favourable when compared with younger mothers (25-29 years). Remarkably, the same can not be said of twin pregnancies in older mothers. Twins fare better when their mother is older than 34 years. In another study, we found higher incidences of velamentous cord insertion in twins after assisted reproduction, compared with naturally conceived twins. The incidence increased along with invasiveness of the applied technique. Since the aetiology of velamentous cord insertion occurs very early in the implantation--phase, we hypothesize that increased embryo manipulation has an effect on the implantation of the human embryo. Other results show that more advantageous pregnancy outcome may be expected when there is maximal implantation potential in assisted reproduction. We first hypothesized that the more advantageous pregnancy outcome in singletons after single embryo transfer (SET) was attributable to a vanishing--twin effect in singletons after double embryo transfer (DET). However, our results indicated higher mean hCG--values in singletons after SET when compared with singletons after DET. As a consequence, we concluded that less good outcomes in singletons after DET are not attributable to an early decease of the embryo. Probably only one embryo implants, but this implantation may be hampered by the other not--implanting embryo.