Case selection and definition
We assessed blood pressure, and performed urinalysis and ultrasound,
including fetal position, fetal growth, and amniotic fluid volume at
each examination, screening for congenital anomalies, when needed. All
maternal and ultrasound data were stored in medical records. In twin
pregnancies, ultrasound was performed in the first trimester to
determine chorionicity and amnionicity. That is, an intertwin membrane
with the ”twin peak” or ”lambda” sign indicates dichorionic twins, and
an intertwin membrane with the ”T” sign indicates monochorionic
twins14.
Maternal renal dysfunction was
defined as a serum creatinine of above 0.8 mg/dL. Preeclampsia was
defined as the occurrence of gestational hypertension (systolic blood
pressure >140 mmHg or diastolic blood pressure
>90 mmHg after 20 weeks of gestation), proteinuria
(>300 mg on 24-hour urine collection), and/or signs of
end-organ dysfunction during pregnancy15. Fetal growth
restriction was defined as a birth body weight of <-1.5 SD for
gestational age in Japan16.