Oral Presentation Society of Obstetric Medicine of Australia and New Zealand ASM 2018

Hypertensive disorders of pregnancy: Australian population data 2004-2013 (#3)

Amanda Henry 1 2 , Stephanie K.Y. Choi 3 , Georgina Chambers 3
  1. School of Women's and Children's Health, University of New South Wales, Sydney, NSW, Australia
  2. Women's and Children's Health, St George Hospital, Kogarah, NSW, Australia
  3. National Perinatal Epidemiology and Statistics Unit, School of Women’s and Children’s Health and Centre for Big Data Research in Health, University of New South Wales, Sydney, NSW, Australia

Introduction: Australia is a high-immigration country, with over a quarter of annual births to overseas-born mothers. How Australian hypertensive disorders of pregnancy (HDP) rates vary by country of birth (COB) is unclear.

Objective/hypothesis: 1) Examine Australian incidence of HDP by mother’s COB 2) Compare small-for-gestational-age (SGA) rates by HDP category using Australian birthweight charts and INTERGROWTH-21st fetal growth charts.

Methods: Population-based cohort study using all singleton birth records (Australian Perinatal Data Collection) 1 January 2004-31 December 2013. Hypertensive disorder status was categorized as no hypertension, pre-existing hypertension-only (EH), pregnancy hypertension-only (gestational hypertension and preeclampsia: GH/PE), and both pre-existing and pregnancy hypertension.

Results: Of 2.78 million singleton births, 72.8% had Australian-born mothers, 8.8% European, 2.9% Middle Eastern/North African, 1.9% Chinese, 2.0% Indian, 1.2% Vietnamese, 1% Filipino, 4.7% other Asian, 4.6% other. For the 2.36 million (85%) where HDP status available, 5.9% had an HDP recorded: 4.9% GH/PE, 0.8% EH, 0.1% both. HDP varied substantially by maternal COB, from 2.1% in Vietnamese-born to 6.5% in Australian-born mothers. Chinese (2.3%), Middle-Eastern/North African (3.2%) and Indian-born (4.3%) mothers also had substantively lower HDP rates than Australian-born. Filipino-born (6.4%) did not. SGA rates were higher in women with HDP than without (p<0.001). These rates also varied substantially by which growth chart was used: Australian birthweight centiles 9.2% SGA if no HDP, 10.8% EH, 12.7% GH/PE, 13.7% both, INTERGROWTH-21st 3.5% SGA if no HDP, 5.6% EH, 7.4% GH/PE, 9.8% both.

Discussion: HDP rates varied substantially by COB, and were more than double in Australian-born mothers than some immigrant groups. Reasons for this could include differing HDP risk-factor profile among immigrant populations. Rates of SGA at birth were higher in women with HDP than without, but varied substantially depending on whether birthweight or prescriptive fetal growth (INTERGROWTH-21st) charts were used, which has implications for clinical practice.