Objective To investigate if chronic hypertension in the absence of sup
erimposed pre-eclampsia is associated with increased perinatal morbidi
ty (especially small for gestational age babies and preterm deliveries
) when compared to the general obstetric population. Design A retrospe
ctive cohort study. Setting A tertiary referral obstetric hospital. Pa
rticipants One hundred and fifty-five pregnant women with chronic hype
rtension who had a diastolic blood pressure of greater than 90 mmHg be
fore 20 weeks or had pre-existing essential hypertension were studied.
The study period was January 1 1991 to June 30 1993. Main outcome mea
sures Perinatal related loss rate, birthweight less than the fifth cen
tile (small for gestational age) preterm delivery, placental abruption
and development of superimposed preeclampsia. Results Women with chro
nic hypertension without superimposed pre-eclampsia had an increased r
ate of small for gestational age babies (10.9 %) compared with the gen
eral population (4.1 %) (odds ratio 2.9 [confidence interval 1.6 to 5.
0]). Women with chronic hypertension without superimposed pre-eclampsi
a did not have a significant increase in preterm delivery or perinatal
loss. Severe hypertension (diastolic blood pressure greater than or e
qual to 110) at less than 20 weeks was associated with a trend to an i
ncreased risk of small for gestational age babies (odds ratio 3.8 [con
fidence interval 1.0 to 13.7]), increased rate of delivery at less tha
n 32 weeks (odds ratio 7.4 [confidence interval 1.9 to 29.5]) and incr
eased rate of superimposed pre-eclampsia (odds ratio 5.2 [confidence i
nterval 1.5 to 17.2]). Women with superimposed pre-eclampsia had the g
reatest perinatal morbidity. Conclusions Women with chronic hypertensi
on without pre-eclampsia have an increased risk of delivering a small
for gestational age baby. Perinatal morbidity and pre-eclampsia is gre
atest in women with severe hypertension at less than 20 weeks. Preterm
delivery is more common in women with superimposed pre-eclampsia.