The placenta is clearly crucial for fetal growth as it provides all the substrates for fetal growth and performs gaseous exchange in fetal life. Some of the associations between IGF system proteins and eventual birth weight are placentally derived components, such as PAPP-A, as IGFs are also important in controlling placentation. A number of tests of placental function demonstrate associations with eventual fetal growth (see p. 162). A view emerged that many complications of pregnancy associated with poor placental function may be due to failure of the so-called 'second wave' of trophoblast invasion in the second trimester. However, more recent studies have suggested that trophoblast invasion takes place as a continuous process during the first half of pregnancy. The process of implantation and early placentation may be crucial in determining fetal growth disorder and there are associations between both the size of the fetus in the first trimester of pregnancy and maternal levels of PAPP-Aand the eventual birth weight of the baby (Fig. 19.1).
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Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.