The extended gestation of fully developed embryos in viviparous reptiles can be the consequence of a lack of appropriate environmental conditions and/or an adaptive contribution to increased offspring viability. I examined the cause and effects of extended gestation in a gekkonid lizard Hoplodactylus maculatus, which delays parturition of developed embryos for up to 9 months from autumn into a second spring. Comparisons of microhabitat temperatures showed that thermal opportunities were equally conducive to birth in autumn and spring. The responsiveness of females to a hormonal stimulant for parturition also did not differ between these seasons. Multiple offspring traits were measured, including body size, locomotory ability and lipid reserves, and were found not to increase with extended gestation. Incorporating these results with previously published evidence for microhabitat thermal variation, I discuss whether delayed parturition may be an adaptive mechanism maintained by the selective pressures of an uncertain thermal environment on components of reproduction, including vitellogenesis, maternal birthing cues and neonatal survival.