Hydroxyprogesterone Caproate/Estradiol Benzoate

This study will evaluate the levels of hydroxyprogesterone caproate and it's metabolites in blood throughout pregnancy
There will be 3 cohorts of subjects
Cohort 1 (6 subjects) will have daily blood draws in the morning at approximately the same time each day for one week following their first dose of Makena and will have blood drawn immediately prior to 2 successive Makena doses during Epoch 1 (24 - 28 weeks) and Epoch 2 (32 - 36 weeks)
Cohort 2 (8 subjects) will have blood drawn to determine the trough concentration 7 days after their first dose of Makena. Subjects will have daily blood draws for one week following a dose of Makena given in Epoch 1 (24 - 28 weeks) and blood drawn immediately prior to 2 successive doses during Epoch 2 (32 - 36 weeks)
Cohort 3 (16 subjects) will have blood drawn to determine the trough concentration 7 days after their first dose of Makena. Subjects will have blood drawn immediately prior to 2 successive doses in Epoch 1 (24 - 28 weeks) and daily blood draws for one week following a dose of Makena given during Epoch 2 (32 - 36 weeks)
A maximum of 10 subjects will be monitored on selected days following a completed course of Makena therapy to determine the terminal elimination phase.