In the general population progesterone supplementation is widely used, is well tolerated, is considered safe, and is beneficial to prevent recurrent pre-term birth and increase birth weight. The investigators experimental findings suggest that PI use during pregnancy is associated with declines in progesterone levels that correlate with fetal growth, and that progesterone supplementation can improve PI-induced fetal growth restriction. The investigators preliminary findings in HIV+ pregnant women suggest that PI-use is associated with declines in progesterone levels, which correlate with birth weight percentile. Since HIV-positive women have higher rates of pre-term delivery and low birth weight that may be magnified by the use of PIs, then progesterone supplementation could be of benefit to neonatal health in the context of HIV-positive pregnancy.