Introduction
During the past decade, the rate of twin pregnancies has remarkably increased, and this is mainly ascribed to the rise in maternal age and the improvements in fertility enhancing treatments.1-3A common adverse outcome for twin pregnancies is intertwin birthweight discordance, defined as the birthweight discrepancy divided by the birthweight of larger twin and multiplied by 100.4 Birthweight discordance has been reported to be related to an increased incidence of fetal intrauterine death, neonatal neurological morbidities, respiratory distress, infection, abnormal acid-base status, or necrotizing enterocolitis.4,5
Though the cause and pathophysiology of rising birthweight discordance in twin pregnancies are not completely understood and mastered, recent studies ascribed it to chorionicity,6 parental race,7maternal vitamin D levels,8 total birthweight, maternal age, education, fetal sex,9 weight gain during pregnancy10 and GHD.
Gestational hypertensive disease (GHD), classified into gestational hypertension (GH), preeclampsia (PE), eclampsia and chronic hypertension (CH),11,12 is one of the most common disorders in pregnancy and its incidence in twin pregnancies is at least double greater than in singletons.13,14 The risk of PE was 2.3% in singletons, 8.1% in dichorionic (DC) twin pregnancies and 6.0% in monochorionic (MC) twin pregnancies. GHD is well recognized as a major risk factor for maternal morbidity, perinatal mortality and preterm delivery.14,15For singletons, the relationship between GHD and fetal growth anomalies has been well established.16 However, studies investigating the association between GHD and birthweight discordance in twin pregnancies have reported differing results. In spite of the previous negative findings that the risk of intertwin birthweight discordance was similar between pregnancies with GHD and normotensive ones,17-19 some other reports have shown that the degree of intertwin birthweight discordance in twin pregnancies is directly correlated with the risk of GHD.20-26
It is crucial to clarify the impact of GHD on intertwin birthweight discordance, as increased risks of perinatal outcomes are associated not only with GHD itself, but also with intertwin birthweight discordance.4,27-29Therefore, the aim of this systematic review was to explore the association between GHD and birthweight discordance in twin pregnancies.