The contribution of assisted conception, chorionicity and other risk factors to very low birthweight in a twin cohort

Objectives To investigate the contribution of assisted conception (assisted reproductive technology and ovulation induction), chorionicity and selected maternal risk factors for very low birthweight. Design Retrospective twin cohort study. Setting Staff model Colorado Health Maintenance Organization. Sample Five hundred and sixty-two twin gestations [assisted = 193 (34%); unassisted = 369 (66%)]. Methods Data were collected from a perinatal database and medical record review. Data were analysed using univariate and multivariable logistic regression analysis. Main outcome measure Very low birthweight. Results Women with assisted twin gestation were more likely to be older, nulliparous, non-smokers, married, have a prior history of a miscarriage and a dichorionic placentation. There was no difference in the distribution of low and very low birthweight, discordant growth or preterm delivery between assisted and unassisted twin gestations. Significant risk factors for very low birthweight were: a prior preterm birth (odds ratio, OR, 3.8, 95% confidence interval, CI, 2, 7), monochorionicity (OR 3, 95% CI 2, 4.7), nulliparity (OR 2, 95% CI 1.3, 3), cigarette smoking (OR 1.8, 95% CI 1, 3) and prior miscarriage (OR 1.6, 95% CI 1, 2). Monochorionicity was significantly associated with adverse perinatal outcomes. Conclusion Assisted conception did not play a significant role in the occurrence of very low birthweight in this cohort. A history of preterm birth and a monochorionic twin gestation were the leading risk factors for very low birthweight. Associated risk factors for very low birthweight were nulliparity, cigarette smoking and a prior miscarriage.