RESULTS
The United States study population included 32,476,039 live births between 2007 and 2020, of which 1.5% received any antenatal corticosteroid prophylaxis. In Nova Scotia, among 116,575 live births between 2007 and 2020, 3.4% received any antenatal corticosteroid prophylaxis. Characteristics of the Nova Scotia cohort stratified by ACS use are shown in Table S1.
In Nova Scotia, rates of any ACS administration did not change significantly between 2007-2016 and 2017-2020 among all deliveries, with rates declining slightly from 3.4% to 3.3% (Table 1). However, the temporal patterns varied by gestational age. For instance, the rate of any ACS administration for women delivering at 28-32 weeks of gestation decreased from 83.1% in 2007-2016 to 74.3% in 2017-2020 (OR 0.59, 95% CI 0.42-0.84; Table 1). On the other hand, the rate of any ACS administration increased significantly among women delivering at 35-36 weeks, from 15.2% in 2007-2016 to 19.6% in 2017-2020 (OR 1.36, 95% CI 1.14, 1.62). Figure 1 shows temporal patterns in any ACS administration by year in each gestational age category. In 2020, 80% of live births at 28-32 weeks gestation received ACS, whereas only 75% of all live births at 33+0 to 33+6 weeks’ gestation and 60% of live births at 34+0 to 34+ 6 weeks’ gestation received any ACS prophylaxis. The rate of any ACS use for women who delivered at 35 weeks increased steadily from 27% in 2017 to 32% in 2019 (Figure 1), while there was no change in ACS rates for infants born at 36 weeks. The proportion of infants at ≥37 weeks gestation who had received ACS was 1.9% in 2016 and this proportion decreased to 1.1% in 2020.
In the United States, rates of any ACS use were lower at each gestational age compared with the same rates in Nova Scotia. However, rates of ACS administration increased significantly and to a much larger extent in the United States between 2007-2016 and 2017-2020 across all gestational age categories (Table 2). For instance, the rate of any ACS administration for women delivering at 33-34 weeks of gestation increased substantially from 18.8% in 2007–2016 to 39.9% in 2017–2020 (OR 2.85, 95% CI 2.85–2.90); among live births at 35-36 weeks of gestation, receipt of any ACS increased from 4.1% in 2007–2016 to 18.5% in 2017–2020 (OR 5.33, 95% CI 5.28–5.38; Table 2). The rate of any ACS use for women who delivered at 35 weeks increased sharply from 14% in 2016 to 27% in 2020, while rates among infants born at 36 weeks’ gestation increased from 7% in 2016 to 16% in 2020 (Figure 1). Among live births at ≥37 weeks gestation, the rate of ACS administration increased from 0.5% in 2016 to 0.8% in 2020.
In Nova Scotia, in 2020, approximately 34% of infants whose mothers received ACS were born at 37 weeks of gestation or greater, while the corresponding rate in the United States was 20%. Rates of ACS use by mode of delivery in Nova Scotia are shown in Table 3; rates were highest among women who delivered by cesarean delivery, in particular those with planned cesarean delivery. Among women who delivered at 35-36 weeks’ gestation by planned cesarean delivery, rates of ACS use increased from 17.6% in 2007-2016 to 23.8% in 2017-2020 (OR 1.46, 95% CI 1.08−1.98; Table 3), while rates of ACS use decreased substantially in women who delivered at 28-32 weeks by cesarean delivery. The latter decrease was observed among both the planned and the in-labour cesarean delivery subtypes. The rate of any ACS use among women who had a spontaneous vaginal delivery at 33-34 weeks of gestation significant increased from 45.4% in 2007-2016 to 54.9% in 2017-2020 (OR 1.46, 95% CI 1.04-2.05).
Temporal trends in the frequency of optimal and suboptimal antenatal corticosteroid use between 2007 and 2020 in Nova Scotia are displayed in Figure 2. Rates of optimal ACS use (live births delivered between 24 and 34 weeks whose mothers received ACS between 24 hours to 7 days before delivery expressed as a proportion of all live births delivered between 24 to 34 weeks) increased from 28% in 2007 to 32% in 2020 (the linear trend was not significant). Rates of suboptimal administration of ACS also increased slightly from 44% in 2007 to 47% in 2020 (linear trend was not significant).