Background: Maternal hyperthyroidism (MH) during late pregnancy is associated with adverse neonatal outcomes but the effects of MH in early gestation when managed in a specialised joint obstetric endocrine clinic setting is unclear. Objectives: To evaluate the obstetric and neonatal outcomes of maternal hyperthyroidism presenting during early gestation. Methods: Endocrine and obstetric record of 40 pregnancies with active hyperthyroidism managed in the antenatal endocrine clinic were retrospectively reviewed. Analysis of outcomes was linked to free T3 (fT3), free T4 (fT4) and TSH levels at first presentation. Outcome variables include: delivery methods, preeclampsia, neonatal weight and gestational age at delivery. Results [mean+-sd]: 85% of patients with MH presented to our service in their first trimester and all were euthyroid by the third trimester and during delivery. At presentation, 15 patients were hyperthyroid (H) [TSH <0.1 + fT4>23 or fT3>6.5 or both] and 25 patients were euthyroid (E). At delivery, the gestational ages of mothers in group H and group E were: (38.7±2.99 v 39.1±1.17; NS). The infant birth weight (IBW) from mothers in group H and in group E were: (3.02±0.71 v 3.39±0.83; p=0.16). The proportion of mothers with low IBW (i.e.<2.5g) in group H was 13% compared to 8% in group E (OR=1.77, 95% CI: 0.22 to 7.96). The caesarian section (CS) rates were higher in the total study cohort (T) compared with the local hospital (C) rate (T=30% v C=18%). CS rate in group H was higher than in group E (33.3% v 28.%, OR=1.28, 95%CI=0.32-3.99) but was not due to differences in the rate of emergency CS between the two groups (13.3% v 16%). Conclusion: Even within a specialised clinic setting, maternal hyperthyroidism at initial presentation increases the likelihood for elective CS and low IBW. Appropriate management of hyperthyroidism is therefore important even at early stages of pregnancy.