Abstract
ObjectiveThe purpose of this study was to clarify the influence of the vanishing twin (VT) on the perinatal outcomes in the surviving singleton and further identify the susceptible window.Study designRetrospective cohort study.MethodsA total of 636 survivors of a vanished co-twin and 11,148 singleton controls were enrolled. The exposed group was further divided into early VT (EVT, VT ≤13 weeks, N = 593) and late VT subgroups (LVT, VT >13 weeks, N = 43) according to the gestational age of the twin vanishing. All participants were conceived through in vitro fertilization (IVF). Perinatal outcomes including gestational age, birthweight, and the incidence of preterm birth (PTB), low birthweight (LBW), small for gestational age (SGA), neonatal intensive care unit (NICU) admission, umbilical cord abnormality, jaundice of the newborn, and oligohydramnios were compared among the groups.ResultsIn our birth cohort, about 5.4% of all singleton deliveries originated from vanishing twin pregnancies. Compared with the singletons, both early and late VT pregnancy had a significantly lower birth weight (3337.57±532.24 g and 2916.05±526.07 g vs. 3446.15±526.07 g; p < 0.001 and p < 0.001), more frequent neonatal jaundice (47.0% and 60.5% vs. 40.6%; p = 0.002 and p = 0.008), and decreased incidence of umbilical cord abnormality (15.5% and 7.0% vs. 19.9%; p = 0.009 and p = 0.034). Newborns in the early VT group were more likely to manifest as SGA (5.4% vs. 3.6%, p = 0.002) and suffered oligohydramnios (5.4% vs. 3.4%; p = 0.008) than the primary singletons. In addition, the gestational age of late VT survivors was shorter than that of the controls (37.25 ± 3.25 vs. 39.04 ± 1.63, p = 0.001) and had a significantly higher risk of PTB (30.2% vs. 6.6%; p < 0.001) and NICU admission (27.9% vs. 9.4%, p < 0.001). All differences except for SGA maintain significance after adjusting for maternal age, BMI, and parity.ConclusionsSingletons with a vanished co-twin had worse perinatal outcomes compared with the original singletons, with LVT burden even much on the survival one. Therefore, close monitoring during the perinatal period was suggested in this type of neonates. Moreover, elective single embryo transfer should also be fully considered which could tackle the problem at its root.
Highlights
In vitro fertilization (IVF), as the final option or the sole solution for infertile couples, has led to more than 8 million births in the world [1]
5.40% (636/11,784) of the singletons born through IVF were from VT pregnancies, among whom 93.24% (593/636) belonged to early vanishing twin (EVT) and 6.76% (43/636) belonged to late vanishing twin (LVT)
The rate of frozen-thawed embryo transfer is significantly higher in the singleton group than in the EVT and LVT groups (56.7% vs. 32.4% and 18.6%, p < 0.001 and p < 0.001)
Summary
In vitro fertilization (IVF), as the final option or the sole solution for infertile couples, has led to more than 8 million births in the world [1]. Vanishing twin syndrome (VTS), defined as the spontaneous reduction of a twin fetus [3], was estimated to occur in 5%–30% IVF/intracytoplasmic sperm injection (ICSI) pregnancies [4, 5]. This reduction could happen in the first trimester named as early vanishing twin (EVT) or in the late pregnancy trimester named as late vanishing twin (LVT) [6]. Different from the primary singletons, those born to VT pregnancies were exposed more or less to an intrauterine environment of twin pregnancy, which was supposed to be related to adverse pregnancy outcomes such as lower birthweight, premature birth (PTB), and even fetal and infant death [7–9]. Heterogeneity of the fetal loss time and the underpower due to the limited samples might lead to contradictions in these studies
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