P46 Does asthma during pregnancy actually follow the ‘one-third’ rule?

IntroductionTraditionally, asthma in pregnancy is thought to follow a ‘one-third rule’ which states in patients with diagnosed asthma, during pregnancy one-third will see worsening symptoms, one-third will enjoy improved control, whilst one-third will experience no changes to their asthma symptoms.1 We set out to test this theory using retrospective data analysis of data collected from a specialist obstetric asthma clinic.MethodsWe carried out retrospective analysis of data collected from an obstetric asthma clinic over one year from October 2018 to October 2019 to assess whether patient’s symptoms were better, unchanged or worse during their pregnancy. Data was reviewed from patients who were in at least their second pregnancy to allow for comparison between the current pregnancy and their earlier pregnancies.Both subjective and objective symptom control was considered. Subjective control was determined by the patient’s impression of their symptom burden, whilst objective control was determined by the number of steroid courses prescribed and the number of hospital admissions.Results48 patients were reviewed in the specialist obstetric asthma clinic, 28 of whom were in at least their second pregnancy. Of these patients, when compared to their previous pregnancies 18% reported better symptom control, 43% reported that their asthma remained unchanged and 39% reported worsening control.Objective data on severity followed this pattern also. The mean number of steroid courses prescribed per patient was 0.2 in those who reported better control, 0.58 in those who reported no change to control, and 1 in those reporting worsening symptoms. Similarly, the number of average number of admissions per patient increased in accordance with subjective severity.Abstract P46 Table 1Objective and subjective severity of asthma during pregnancy Subjective control (compared to previous pregnancies) Percentage of patients No of steroid courses Average number of steroid courses per patient Number of admissions Average number of admissions per patient Better 18% (n=5) 1 0.2 1 0.2 Same 43% (n=12) 7 0.58 3 0.25 Worse 39% (n=11) 11 1 3 0.27 ConclusionsOur analysis confirms that asthma control in pregnancy does not follow the simple one-third rule as previously speculated. When using subjective and objective measurements, a greater proportion of patients experienced either worsening asthma control or no changes to control during pregnancy, with only a small percentage reporting that th