Table 3.
Summary of published literature regarding vanishing twin syndrome and associated perinatal outcomes.
| Reference | Study type/sample size | Diagnosis of vanishing twin | Gestational age | Birth weight | Other |
|---|---|---|---|---|---|
| Dickey et al.1 | Prospective observational/709 | Spontaneous reduction in one or more gestational sacs or embryos before 12 weeks | After spontaneous reduction, the average length of gestation was shortened by 4–250 days | Birth weight was inversely related to the initial number of gestational irrespective of the final birth number | None |
| La Sala et al.2 | Retrospective/686 | Pregnancies that began as twins but in which one embryo with positive heartbeat was lost during the first trimester or found to be lost in a subsequent ultrasonogram | Rates of preterm birth were similar among survivors of vanishing twin (16.7%) and control singletons (15.9%) | Rates of LBW were similar among survivors of vanishing twin (10.7%) and control singletons (12.9%) | Similar results were found when conventional IVF and IVF plus ICSI pregnancies were separately evaluated |
| Pinborg et al.4 | National registry/642 survivors of a vanishing co-twin, 5237 singletons from single gestations, and 3678 twins from twin gestations | One fetus with positive fetal heart rate plus a gestational sac/fetus without fetal heart beat at 8 weeks | Shorter length of gestation in survivors (38.9 weeks) compared to control singletons (39.5 weeks) | 1.7 times and 2.1 times higher odds of LBW and VLBW in singleton survivors of a vanishing twin after 8 weeks of gestation, respectively | Correlation between spontaneous reduction later in pregnancy and risk of neurological sequelae |
| Pinborg et al.7 | National registry/642 survivors of a vanishing co-twin, 5237 singletons from single gestations, and 3678 twins from twin gestations | One fetus with positive fetal heart rate plus a gestational sac/fetus without fetal heart beat at 8 weeks | Not reported | The odds of SGA infants were 1.5 times higher in survivors than in singletons. There was a significant inverse correlation between SGA and the gestational age at the time of vanishing | None |
| Shebl et al.8 | Case–control/794 | One fetus with positive fetal heart rate plus a gestational sac/fetus without fetal heartbeat during a first trimester ultrasonogram | No differences were observed in terms of duration of gestation | The frequency of LBW (26.1% vs 12.0%) and SGA (32.6% vs 16.3%) was significantly higher in vanishing twin survivors | None |
| Almog et al.9 | Retrospective case control study/1373 singleton deliveries and 57 cases of vanishing syndrome | Vanishing twin syndrome was defined in cases where two fetal heart beats were demonstrated between 6 and 7 weeks and one fetal heart beat was demonstrated thereafter, but before 12 weeks of gestation | Mean gestational age was lower (35.1 weeks) in compared to singleton controls (38.2 weeks) | Incidence of LBW (33.3%) and VLBW (3.5%) was higher in vanishing twin survivors compared to singleton controls, respectively | None |
| Rodríguez-González et al.11 | Retrospective chart review of donor oocyte pregnancies/399 | Spontaneous loss of one or more embryos after identifying heart activity during the first trimester | Gestational age at delivery was similar in both groups | Birth weight at delivery was similar in both groups | Preterm and term spontaneous rupture of membranes was increased in vanishing twin survivors |
| Mansour et al.12 | Retrospective cohort study/2829 | Presence of one or more additional empty gestational sacs or fetuses with no heartbeat at 6–7 weeks and 11–12 weeks of gestation | Not reported | There was no statistically significant difference in the mean gestational age between the groups | Live birth rate was higher significantly higher in singleton pregnancies after vanishing fetuses |
| Evron et al.20 | Retrospective/278 vanishing twins were compared with 1801 dichorionic twins and 252,994 singletons | Pregnancies that started with double fetal sacs and spontaneously reduced into one during the first trimester | Not reported | Increased odds of IUGR (2.7 times) and LBW (6.9 times) in vanishing twin survivors compared to controls | Increased odds of gestational diabetes, low APGARS and perinatal mortality in vanishing twin survivors |
| Luke et al.21 | Society for Assisted Reproductive Technology national database/21,535 singleton deliveries | First trimester loss of fetal cardiac activity | Increased odds of late PTB (1.73 times) and early PTB (2.56 times) in vanishing twin survivors compared to controls | Increased odds of LBW (2.09 times) and VLBW (1.94 times) in vanishing twin survivors compared to controls | None |
IVF: in vitro fertilization; LBW: low birth weight; VLBW: very low birth weight; SGA: small-for-gestational age; PTB: preterm birth; ICSI: intracytoplasmic sperm injection; IUGR: intrauterine growth restriction.