Associated obstetric and perinatal determinants of vanishing twin pregnancies
Authors: Márton Virág 
Published: March 2021

A retrospective cohort study was carried out to reveal the characteristics and the perinatal outcome of vanishing twin pregnancies after spontaneous conception and after assisted reproductive techniques (ART). Vanishing twin (VT) syndrome, defined as the disappearance of one of two embryos with the survival of the co-twin during the first trimester, has been known for more than four decades. Due to the high and ever growing number of assisted reproductive treatments, the incidence of twin pregnancies and thus of vanishing twin syndrome is high. Recent studies have only examined vanishing twins after ART, but we hypothesized that there is a difference in perinatal outcomes between VT pregnancies, depending on the mode of conception, possibly reflecting the potential differences between underlying pathomechanisms. Our study consisted of two parts. We initiated the first study to compare obstetric and neonatal outcomes between the survivors of VT pregnancies and matched originally singleton control pregnancies, and a second study to evaluate whether VT pregnancies after spontaneous conception have a more adverse perinatal outcome than those conceived after assisted reproductive techniques. The study involved 316 VT pregnancies: 81 after in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) and 235 after spontaneous conception. Their data were derived from databases in a 22-year study period at the Department of Obstetrics and Gynecology, University of Szeged, Szeged, Hungary. Our results proved that the frequency of VT pregnancies was significantly higher after natural conception than after ART. A comparison of VT pregnancies demonstrated a higher rate in pregestational and gestational diabetes mellitus (GDM) in IVF/ICSI cases than in spontaneously conceived VT pregnancies. Significant differences in the prevalences of pregnancies and intrapartum complications, and adverse neonatal outcomes were observed in vanishing twins born after IVF/ICSI as compared with those born after implantation without medical assistance, suggesting that adverse perinatal outcome in IVF/ICSI VT pregnancies may be more related to ART or infertility and underlying chronic diseases. Previous induced abortion and second-trimester fetal loss indicated an increased risk of VT pregnancies, while GDM and prematurity of previous pregnancies predicted VT and growth retardation, particularly in the spontaneously conceived VT group. Diabetes is classically defined as being associated with a higher miscarriage rate. We observed a higher recurrence rate of gestational diabetes and increased incidence of pregestational and gestational diabetes mostly in IVF/ICSI VT pregnancies, suggesting that diabetes may share a pathomechanism with VT. After identifying the causes that lead to vanishing twin syndrome, GDM, chronic maternal diseases, advanced maternal age and placentation anomalies all represented independent risk factors for VT following IVF/ICSI. It can be established that the VT phenomenon was a major prognosticator of intrauterine growth restriction for the remaining fetus in VT pregnancies after ART. In conclusion, according to our results, VT is quite frequent. VT pregnancies had a lower prevalence and a worse perinatal outcome following IVF/ICSI as compared with those of their spontaneously conceived counterparts.