Cover Story

Progesterone in early pregnancy:
measuring it, giving it

By Laurie Jane McKenzie, MD, and John E. Buster, MD

When during the first trimester is it valuable to measure levels of this hormone and when is it a waste of time? Will giving your patients progesterone supplements help prevent miscarriage? Are they safe?

Progesterone has been aptly named the "hormone of pregnancy," because in preparing the endometrium for embryo implantation and facilitating endometrial development, it's critical to the very survival of a pregnancy. In addition, this key hormone inhibits the rejection of T cell-mediated tissue and also decreases myometrial activity and sensitivity throughout pregnancy.¹ More than a quarter century ago human studies dramatically demonstrated the importance of the corpus luteum's production of progesterone in pregnancy through classic experiments in which they surgically removed this ovarian "yellow body" in early pregnancy. When they performed this luteectomy before 7 weeks' gestational age, the pregnancy almost always led to miscarriage. They found that administering progesterone could prevent miscarriage in women who had a luteectomy.²

More than 25 years before that experiment, progesterone was first extracted from the corpus luteum, characterized as a steroid, and later purified. Of course, we now refer to any steroid that exhibits progesterone-like activity as a progestin or progestogen. All progestins/progestogens transform the endometrium following estrogen-induced proliferation.

Progesterone is produced predominantly by the ovaries, and in small measure by the adrenal glands, and at a rate of less than 1 mg/day before ovulation. After ovulation and corpus luteum formation, this increases to 20 to 30 mg/day. Then during pregnancy, it climbs dramatically, reaching 200 to 400 mg/day at term. Until approximately 7 weeks' gestation, increased progesterone production is dependent on the corpus luteum and thereafter on the placenta, the so-called "luteal-placental shift" which occurs between 7 and 10 weeks (Table 1 and Figure 1).

TABLE 1
Progesterone production before and during pregnancy

Graph of midcycle hormone levels is adapted with permission from: Hoff JD, Quigley ME, Yen SS. Hormonal dynamics at midcycle: a reevaluation. J Clin Endocrinol Metabol. 1983;57:792-796. Copyright 1983, The Endocrine Society.

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