Chronic hypertension: Risk of stillbirth higher for black than for white women

In the largest study of its kind in the UK, doctors from King's School of Life Course Sciences have found that ethnicity has a major impact on the risk of complications for pregnant women with long-term high blood pressure (chronic hypertension in pregnancy). Differences in the incidence of stillbirth were particularly marked: five times higher for Black women than White women and almost three times higher for Asian women than White women.

Chronic hypertension affects about three per cent of pregnancies worldwide and is becoming more common with rising maternal age and levels of obesity. It is associated with several severe complications including pre-eclampsia, stillbirth, fetal growth restriction and preterm birth.

Outside pregnancy ethnic origin is routinely considered when prescribing medication for high blood pressure but this is not the case for pregnant women.

To better understand whether tailoring treatment for chronic hypertension to ethnicity during pregnancy could be beneficial, the team analyzed 4,481 pregnancies from three NHS obstetric units over 14 years. All these women had chronic hypertension and 2,122 were White, 1,601 were Black and 379 were Asian.

After adjusting for a range of other demographic factors (deprivation index, maternal age, parity, BMI, smoking history and year of delivery) the team calculated how often complications associated with chronic hypertension in pregnancy occurred.

Their results, published in the journal Ultrasound in Obstetrics and Gynaecology, showed that each complication was more common for Black women than White women. The risk of stillbirth was five times greater (3.1% versus 0.6%), preterm birth nearly double (21% versus 11%) and fetal growth restriction more than double (16% versus 7.4%).

Asian women, compared to White women, were also at increased risk but to a lesser extent: stillbirth 1.6% versus 0.6%, preterm birth 20% versus 11% and fetal growth restriction 12% versus 7.4%.

Dr Louise Webster, Clinical Lecturer in the Department of Women & Children's Health, said of the study:

'We cannot yet explain these results. Previous studies have found the same to be true in the USA but researchers suggested that this was due to inequalities in access to healthcare. This now seems unlikely to be the sole cause as our analysis took account of deprivation and, although barriers to healthcare are more complex than just its cost, we would have expected the affect to be reduced in the UK where the NHS is free to use.

Further research is needed to establish what other factors could be involved and whether tailoring blood pressure medication to ethnicity could improve outcomes for pregnant women and their babies.'

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