Perinatal mortality in gestational hypertensive versus non-hypertensive twin pregnancies, U.S. matched multiple birth data 1995–2000.

HR = Hazard ratio; CI =  confidence interval.
*Hazard ratios adjusted for maternal race, marital status, age, education, parity, smoking, other maternal major illnesses, fetal sex, mode of delivery and twin-cluster level dependence in Cox regression models.
**There were a significant number of perinatal deaths with missing birth weights.
t Gestational age group-specific mortality rates and hazard ratios were calculated using the number of foetuses at risk and the number of perinatal deaths in the time interval specified.