Progesterone helps maintain the uterine lining so that an embryo can implant and grow. If you have low levels of progesterone, you may have difficulty getting pregnant or maintaining a pregnancy. Progesterone production rises after ovulation; if you don't ovulate, your progesterone levels remain low because the corpus luteum, the leftover remnant of the follicle that originally contained the ovulated egg, produces progesterone. Progesterone deficiency does not prevent ovulation.
Causes
Progesterone deficiency may stem from poor follicle production in the first half of the menstrual cycle. An abnormal follicle won't produce an adequate amount of progesterone in the second half of the menstrual cycle, according to the International Council on Infertility Information Dissemination, or INCIID. A smaller-than-normal or poor quality follicle may still produce an egg, so you may ovulate. But the abnormal corpus luteum may produce lower-than-normal amounts of progesterone. Some women produce lower-than-normal levels of progesterone even when the corpus luteum is normal; this condition, called luteal phase defect or deficiency, can disrupt a pregnancy.
Effects
The embryo needs the increased blood supply and nutrients supplied by progesterone's effects on the uterine lining. Without progesterone, the embryo cannot implant or may start to implant and then die from lack of nutrients, resulting in a miscarriage. An average progesterone level in the first 5 to 6 weeks of pregnancy is 12 to 20 ng/ml. Lower levels can indicate a problem. Since progesterone causes a slight rise in body temperature, checking your temperature after ovulation can help you determine whether your progesterone levels have risen, but won't indicate whether your progesterone rise is adequate to maintain a pregnancy.
Timing
Women with luteal phase deficiency may have short menstrual cycles. Normally progesterone maintains the uterine lining for around 12 days after ovulation even if you don't get pregnant. Since ovulation occurs, on average, around day 14 of a 28-day menstrual cycle, this means that progesterone keeps the lining intact until around day 26, when it starts to break down. By day 28, your menstrual cycle arrives. If you have a luteal phase defect, your lining begins to break down by day 10, meaning the pregnancy is lost.
Considerations
If you have low progesterone levels, taking progesterone supplements may help prevent pregnancy loss. Take progesterone supplements only after you ovulate; taking progesterone in the first half of the menstrual cycle can prevent ovulation. Progesterone supplements will not prevent miscarriage not associated with low progesterone levels. Checking estrogen levels during the first half of your menstrual cycle may help determine whether you're producing enough estrogen to make a good follicle. In the second half of the cycle when you're not trying to get pregnant, an endometrial biopsy, which is the removal and testing of a small piece of the uterine lining to see whether the tissue shows the proper stage of development, can help determine whether you need more progesterone.
References
- INCIID: Luteal Phase
- Kimball's Biology Pages; Hormones of the Reproductive System; John Kimball, Ph.D.
- California Association of Natural Family Planning; Are Low Progesterone Levels Easily Fixed? ; Mary Davenport, M.D.; January 2007
- American Pregnancy Association; Concerns Regarding Early Fetal Development; Oct. 2008
