Consequences of vanishing twins in IVF/ICSI pregnancies.
BACKGROUND
Spontaneous reductions are a possible cause of the increased morbidity in IVF singletons. The aim of this study was to assess incidence rates of spontaneous reductions in IVF/ICSI twin pregnancies and to compare short- and long-term morbidity in survivors of a vanishing co-twin with singletons and born twins.


METHODS
We identified 642 survivors of a vanishing co-twin, 5237 singletons from single gestations and 3678 twins from twin gestations. All children originated from pregnancies detected by transvaginal sonography in gestational week 8. By cross-linkage with the national registries the main endpoints were prematurity, birth weight, neurological sequelae and mortality.


RESULTS
Of all IVF singletons born, 10.4% originated from a twin gestation in early pregnancy. Multiple logistic regression analyses adjusted for maternal age, parity and ICSI treatment showed for birth weight <2500 g an odds ratio (OR) of 1.7 [95% confidence interval (CI) 1.2-2.2] and for birth weight <1500 g OR 2.1 (95% CI 1.3-3.6) in singleton survivors of a vanishing twin versus singletons from single gestations; corresponding figures were seen for preterm birth. This increased risk was almost entirely due to reductions that occurred at >8 weeks gestation. We found no excess risk of neurological sequelae in survivors of a vanishing co-twin versus the singleton cohort; however, OR of cerebral palsy was 1.9 (95% CI 0.7-5.2). Furthermore, we observed a correlation between onset of spontaneous reduction, i.e. the later in pregnancy the higher the risk of neurological sequelae (r = -0.09; P = 0.02). Adjusted OR of child death within the follow-up period was 3.6 (95% CI 1.7-7.6) in the survivor versus the singleton cohort.


CONCLUSIONS
One in 10 IVF singletons originates from a twin gestation. Spontaneous reductions that occur at >8 weeks gestation are one of the causes for the higher risk of adverse obstetric outcome in IVF singletons.
The Fertility Clinic, The Juliane Marie Center, Copenhagen University Hospital, Rigshospitalet, Denmark. apinborg@rh.hosp.dk
Anja
A
Pinborg
Ojvind
O
Lidegaard
Nina
N
la Cour Freiesleben
Anders Nyboe
AN
Andersen
D000022:Abortion, Spontaneous; D001724:Birth Weight; D002547:Cerebral Palsy / Q000175:diagnosis; D015331:Cohort Studies; D004200:Diseases in Twins; D005260:Female; D005307:Fertilization in Vitro / Q000009:adverse effects*; D005327:Fetal Resorption; D005865:Gestational Age; D006801:Humans; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome; D012042:Registries; D012307:Risk Factors; D020554:Sperm Injections, Intracytoplasmic / Q000009:adverse effects*; D013997:Time Factors; D016896:Treatment Outcome; D014427:Twins; D016216:Ultrasonography, Prenatal