Icon is a water miscible type II synthetic pyrethroid insecticide based on active ingredient lambda cyhalothrin (10% w/w). It is used in Sri Lanka as an adulticidal indoor spray against malaria vector mosquitoes. The goal of this study was to assess the effects of Icon on pregnancy outcome of rats when exposed during early pregnancy (days 1-7). Icon was gavaged daily for 7 consecutive days in three different doses; 63, 83, or 125 mg/kg/day (active ingredient; lambda cyhalothrin; 6.3, 8.3, 12.5 mg/kg/day), respectively. Several parameters of reproduction and pre- and post-natal development were monitored. The results show that Icon is detrimental to pregnancy outcome (in terms of quantal pregnancy, number of uterine implants, implantation index and foetal deaths) but induced no detectable developmental defects. The anti-reproductive effects of Icon were mainly due to increased pre-implantation losses. Enhancement of post-implantation losses played a subsidiary role. These effects resulted from multiple mechanisms: maternal toxicity, stress, uterotropic activity and embryo-foetotoxicity. Further progesterone had a protective effect against Icon induced anti-reproductive actions. Overall, the results suggest that exposure to Icon during early gestation may result in a threat to pregnancy.