Pre-eclampsia and late fetal growth restriction.

There is a strong but complex relationship between fetal growth restriction and pre-eclampsia. According to the International Society for the Study of Hypertension in Pregnancy the co-existence of gestational hypertension and fetal growth restriction identifies pre-eclampsia with no need for other signs of maternal organ impairment. While early-onset fetal growth restriction and pre-eclampsia are often strictly associated, such association becomes looser in the late preterm and term periods. The incidence of pre-eclampsia decreases dramatically from early preterm fetal growth restriction (39-43%) to late preterm fetal growth restriction (9-32%) and finally to term fetal growth restriction (4-7%). Different placental and cardiovascular mechanism underlie this trend: isolated fetal growth restriction has less frequent placental vascular lesions than fetal growth restriction associated with pre-eclampsia; moreover, late preterm and term fetal growth restriction show different patterns of maternal cardiac output and peripheral vascular resistance in comparison with pre-eclampsia. Consequently, current strategies for first trimester screening of placental dysfunction, originally implemented for pre-eclampsia, do not perform well for late-onset fetal growth restriction: the sensitivity of first trimester combined screening for small-for-gestational age newborns delivered at less than 32 weeks is 56-63%, and progressively decreases for those delivered at 32-36 weeks (43-48%) or at term (21-26%). Moreover, while the test is more sensitive for small-forgestational age associated with pre-eclampsia at any gestational age, its sensitivity is much lower for small-for-gestational age without pre-eclampsia at 32-36 weeks (31-37%) or at term (19-23%).