QUESTION OF THE MONTH
September 2000.
A normal pregnancy requires a healthy embryo and a healthy mother establishing optimal reciprocal connections in at least three basic areas, immunologic, hemodynamic and nutritional. One morphologic evidence of such adequacy seems to be the correct penetration of cytotrophoblast into the distal portion of the spiral arterioles providing the necessary vasodilatation of the maternal placental vascular bed.
However, placental bed biopsy material show that normal pregnancies may have some spiral arterioles with less than optimal connections. Also, cases of fetal growth restriction without clinical expression of pre-eclamptic signs will show significant proportions of inadequate feto-maternal connections. Furthermore, in all these normal and clinically abnormal entities, one can see arterioles with inadequate cytotrophoblast penetration next to arterioles with adequate connections. So, it does not seem to be just a qualitative nor quantitative inadequacy making the difference between normal and pathological pregnancies.
Hypoxia has been postulated as the triggering condition for this inadequate penetration or invasion of cytotrophoblast into the final portion of the spiral arterioles. But, how can this hypoxic environment affect only some and not all connections ? How can this hypoxia affect one and not the closest neighboring arteriole ? Do we have pockets where hypoxia is more marked than in other places ? Hypoxia affects only those coinciding with a specific stage (critical) of utero-placental development ? Do we need hypoxia plus another factor(s)?