Purpose The corrections necessary to estimate the risk for Down syndrome in twin pregnancies have been pointed out. We performed a nested controlled study to evaluate the validity of these corrections in dichorionic twins conceived by IVF. Methods Detailed clinical data was collected from the medical records. Twins were matched with a contemporaneous cohort of spontaneously conceived singleton pregnancies that serve as reference in a 1 to 4 ratio. All patients had their entire obstetrical care at our Hospital. The Student t-test was used for group comparisons and a p-value <0.05 was considered significant. Results Nineteen sets of normal twins concordant in size and with appropriate weight for gestational age were matched with 80 normal and mature newborns. Significant differences between groups were found for maternal age, gestational age at delivery and newborn weight (all p <0.01). No statistical differences were noted for the levels of the biochemical markers expressed as multiples of the median. However, a 15 % closer approximation to the laboratory median for PAPP-A and a 10 % closer approximation to the laboratory median for free β-hCG was evident in twins when compared to the reference group. Conclusions These findings support the methods used to estimate the risk for Down syndrome in dichorionic twin pregnancies conceived after IVF. A future study with a larger sample size could confirm if the laboratory corrections done on the combined screening test improve the predictability of Down syndrome in dichorionic twin pregnancy conceived by IVF when compared to singleton pregnancies.

These findings suggest that the fetal and maternal baseline circulatory operational capacities of TNFα are independent of each other and tuned differently. This differential regulation of TNFα in fetal and maternal circulation at the end of pregnancy may be guided to protect the fetus from the systemic inflammatory response that is essential for the mechanisms of labor to proceed in the mother.