Stillbirth 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 stillbirths 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 stillbirths in the time interval specified.

HR：风险比（Hazard ratio）；CI：置信区间（confidence interval）。
* 本研究Cox回归模型所得风险比已校正产妇种族、婚姻状况、年龄、受教育程度、产次、吸烟情况、其他母体重大疾病、胎儿性别、分娩方式及双生子集群水平相关性的混杂因素。
** 大量死胎病例存在出生体重缺失数据。
t 胎龄组特异性死亡率与风险比，通过指定时间区间内处于死胎风险中的胎儿数与死胎数计算得到。