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Sheep have been produced globally for centuries for meat, wool, skin, and milk, yet neonatal mortality in lambs remains high at 15–20%. Low birthweight is the leading contributor to neonatal loss, underscoring the need to understand maternal factors that influence fetal development. This study tested the hypotheses that (1) higher maternal progesterone concentrations during early pregnancy are associated with increased neonatal birthweight, and (2) greater gestation length, maternal age, and maternal weight correspond to greater fetal development. Pregnant ewes (n = 27) carrying a single fetus were maintained under uniform management at the Eastern Agricultural Research Station. Daily blood samples were collected from days 6 to 25 of gestation, and circulating progesterone was quantified by radioimmunoassay. Ewe weight was recorded on the day of breeding, and lamb weight was measured within one hour of birth and stratified into terciles for statistical analysis. Multiple maternal variables were analyzed using PROC MIXED (SAS), with data reported as mean ± SEM. Maternal age, weight, and progesterone concentrations did not differ among birthweight terciles. However, gestation length was significantly associated with neonatal weight (P = 0.01): ewes producing the lightest lambs had shorter pregnancies compared with those producing the heaviest lambs, while the mid-tercile did not differ from either group. As gestation length was the only maternal factor associated with birthweight, future research should investigate environmental and physiological determinants of gestation length to improve neonatal survival in sheep production systems.