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.