Thyroid dysfunction in pregnancy - a retrospective observational analysis of a Maltese cohort

Abstract

Background: Thyroid dysfunction is known to adversely affect pregnancy. This studyevaluates the prevalence of thyroid disorders and explores their associationwith pregnancy complications/comorbidities and modes of delivery in the Maltesepregnant population over a ten year period. Design: A population based observational study. Method: We analysed data from the National Obstetrics Information Service of theDepartment of Health Informations and Research (NOIS) for all births deliveredin Malta between 2006 and 2016. Cases identified and recorded by NOIS to have had some form of thyroiddysfunction during pregnancy were confirmed by cross-referencing with laboratory results found in patients’medical records and/or iSOFT® database system. Using the Statistical Packagefor the Social sciences (SPSS®) demographic data, pastobstetric and medical history and obstetric outcomes were analysed forpregnancies with thyroid dysfunction and compared to data pertaining to pregnancies in euthyroid patients, that is those with no recorded thyroid dysfunction on NOIS. Chi square/Fisher'sexact test were used to compare categorical variables while ANOVA/Mann-WhitneyU test was used to compare continuous variables. Statistical significance wasdefined by a two-sided p value <0.05. Results: Data was available for 46,283 women (mean [SD] age = 29.2 [5.4] years).587 pregnancies (1.3%) suffered from thyroid dysfunction. Of these, 67.3% werehypothyroid, 3.2% had hyperthyroidism, 28.3% had isolated hypothyroxinaemia(IHT) while 1.2% had a history of thyroid carcinoma. Patients with IHT andhypothyroidism were older than euthyroid patients (p < 0.001). IHT and hypothyroid patients had astatistically significant higher body mass index (BMI) than euthyroid women(p=0.001 for hypothyroid women, p = 0.035 for IHT). Hypothyroid and IHT women were more likely to have had aprevious lower segment caesarean section (p=0.043, and 0.006respectively). Type 1 diabetes and gestational diabetes p = 0.012) were more common associatedcomorbidities in hypothyroid pregnancies. Offspring of patients with IHT had ahigher birth weight than those born to euthyroid patients (p=0.009). Patients with hyperthyroidism were found to havea significantly increased risk of early preterm delivery before 34 weeks ofgestation and were also more likely to have suspected intrauterine growthrestriction and low mean birth weight. We report no significantdifferences in past history of obstetric loss, antenatal complications, mode ofdelivery, gestational age at delivery and postpartum haemorrhage rates acrossthyroid categories. Conclusions: Available evidence suggests that thyroid dysfunction is more likely in thesetting of older age, and higher body mass index. Moreover, it impacts on neonatalbirth weight, rates of early preterm delivery and intrauterine growthrestriction.