DebateThe impact of fetal gender on prematurity in dichorionic twin gestations after in vitro fertilization

Background: Impact of fetal gender on prematurity has been primarily investigated in singleton pregnancies. In an attempt to understand better how fetal gender may affect gestational length in twin gestations after in vitro fertilization, same-sex twins and opposite twins were compared for pregnancy duration. Methods: This study evaluated 113 women at ages 20 to 39 years with consecutive dichorionic-diamniotic twin gestations after assisted reproduction. All pregnancies were results of fresh in vitro fertilization (IVF) cycles with use of autologous oocytes and sperm and were delivered at up to 37 weeks of gestation at a University-based high-risk, maternal-fetal medicine unit. Results: Both groups did not differ in baseline characteristics, such as maternal ages, indications for fertility treatments, number of previous IVF attempts, body mass index and parity. Opposite sextwins, however, presented with significantly shorter gestational age at birth (32.9 +/3.4 weeks) than same-sex twins (34.3 +/2.5 weeks), (p < 0.05). Younger maternal age was also associated with shorter pregnancy duration (p < 0.05). Conclusions: Fetal gender mix serves as risk factor for more significant prematurity in dichorionic-diamniotic twins after assisted reproduction with opposite sex twins at higher risk than same sex-twins. Background Assisted reproduction considerably contributes to worldwide increases in twin pregnancies in industrialized countries [1,2]. In comparison to singleton pregnancies twin gestations are associated with a significantly higher risk for prematurity and, consequently, prematurity-associated adverse perinatal outcome [3]. To prospectively identify women with twin pregnancies at risk for prematurity is, therefore, crucial. A variety of predictive factors for prematurity risk, such as maternal age, race or obstetric history (such as previous preterm birth) and fetal gender, is well-established according to population-based surveys of mainly spontaneously conceived singleton and twin pregnancies [4-6]. How patients conceive (i.e. naturally or via assisted reproduction) should effect maternal risk factors for preterm birth, like maternal age, race or prior preterm birth [4,5,7]. Mode of conception appears to affect other risk factors, such as fetal gender and chorionicity. For example, Cooperstock et al. described significantly lower prematurity rates in female/female twins when compared to female/male twins [8]. Opposite sex-twins are always dichorionic, while same-sex twins are either monochorionic or dichorionic. Monochorionicity goes along with a significantly higher risk for preterm birth and adverse perinatal outcome than dichorionicity [9]. The lower prematurity rates in opposite-sex twins might, therefore, be at least partly related to chorionicity, as also suggested by Tan et al. [10]. In addition to a potential bias because of chorionicity, the distribution of monoand dichorionicity differs considerably between spontaneous twins those conceived via assisted reproductive technology (ART). While monochorionicity * Correspondence: andrea.weghofer@meduniwien.ac. at 1 Department of Obstetrics & Gynecology, Medical University Vienna, Vienna,