Chronic Medical Conditions Influence Prescribing of
Antibiotics in Pregnancy
Meeraus, WH1,2; Petersen, I2; Gilbert, R1
1. UCL, Institute of Child Health, MRC Centre of Epidemiology for Child Health
2. UCL, Department of Primary Care and Population Health
Introduction
Methods
One third of women in the UK are prescribed oral
antibiotics in pregnancy*. Factors associated with
antibiotic prescribing include age and social
deprivation, but information on the influence of
chronic medical conditions (CMCs) is lacking. We
examined the hypothesis that women with CMCs
have higher rates of oral antibiotic prescribing in
pregnancy, using primary care data from The Health
Improvement Network.
 We identified a cohort of 112,901 pregnant women aged 15-50 in The Health Improvement
Network.
 Chronic medical condition (CMC) status was defined using an algorithm based on prescriptions
received for CMC management in the 1-year period prior to the start of pregnancy.
 We calculated the proportion of women receiving one or more antibiotic prescriptions in
pregnancy and the average number of antibiotic prescriptions per pregnancy, both by CMC
status.
 Poisson regression was used to account for the effect of age, social deprivation, calendar-year,
smoking, illicit drug use, preterm birth, multiple birth (e.g. twin/triplet), problem alcohol use and
obesity on the rate of antibiotic prescribing in pregnancy.
* Petersen, J Antimicrob Ther, 2010.
What is The Health Improvement Network?
How did we identify individuals with chronic medical conditions?
The Health Improvement Network (THIN) is a database containing anonymised
patient records from almost 500 primary care practices in the UK. The
database contains information on 9.2 million patients and covers 5.7% of the
population. Data on diagnoses, symptoms, and treatments are captured
prospectively on all patients registered at participating practices. Demographic
data and secondary data are also available.
Individuals with chronic medical conditions (CMCs) were identified based on repeat prescriptions in their medical
records for drugs (other than antibiotics) used to treat chronic and semi-chronic conditions such as diabetes,
hypertension, depression, and arthritis. Each woman’s medical records were searched for 23,030 different drug
formulations used in the management of CMCs. Women were considered to have a CMC if they received 2+
prescriptions from the same drug class in the 1-year period prior to pregnancy, and if there was less than a 4month gap between issue of consecutive prescriptions.
Results
 Out of 112,901 women, 18,841 (17%) women were classified as having a chronic medical condition (CMC).
 The proportion of women receiving one or more antibiotic prescriptions in pregnancy was greater among women with CMCs than women without CMCs (Figure 1).
 On average, women with CMCs received more antibiotic prescriptions in pregnancy than women without CMCs (Figure 2).
Figure 1. Proportion of women receiving one or more antibiotic prescriptions in pregnancy.
(Error bars represent 95% confidence intervals.)
Figure 2. Average number of antibiotic prescriptions received in pregnancy.
(Error bars represent 95% confidence intervals.)
50%
43%
45%
Proportion of Women
40%
35%
31%
30%
25%
20%
15%
Number of Antibiotic Prescriptions
1.0
0.9
0.79
0.8
0.7
0.6
0.4
0.3
10%
0.2
5%
0.1
0%
0.0
Women WITH Chronic Medical Conditions
0.47
0.5
Women WITHOUT Chronic Medical
Conditions
Women WITH Chronic Medical
Conditions
Women WITHOUT Chronic Medical
Conditions
 In univariate analysis, women with CMCs were 42% more likely to be prescribed antibiotics in pregnancy than women without CMCs (Incident Risk Ratio (IRR) = 1.42,
95% CI: 1.39 - 1.45).
 After adjustment for age social deprivation, calendar-year, smoking, illicit drug use, preterm birth, multiple birth (e.g. twin/triplet), problem alcohol use and obesity there
was still an association between CMCs and antibiotic prescribing in pregnancy (IRR = 1.37, 95% CI: 1.34 - 1.40).
Conclusions
Where can I get more information?
Chronic medical conditions (CMCs) influence a woman’s risk of being prescribed antibiotics in pregnancy.
Women with CMCs were 37% more likely to be prescribed antibiotics in pregnancy than women without
CMCs. CMCs should be accounted for in analyses of potential associations between antibiotics and
pregnancy outcomes.

Flickr photos courtesy of: ajr628, mahalie, Christopher Hester, HTloveHL, michaelll, oliver.dodd, sparktography, and Veritas Supermarcados.

For further information, please email Wilhelmine
Meeraus at w.meeraus@ich.ucl.ac.uk.
Ms Meeraus is funded by a UK Medical Research
Council PhD Studentship.