Progesterone is a steroid hormone produced by women both during the monthly reproductive cycle and during pregnancy. It serves important roles in helping to prepare the body for pregnancy and maintaining pregnancy, and is also responsible for some of the symptoms of early pregnancy. Understanding the role of progesterone in first trimester pregnancy will help you anticipate your early pregnancy feelings and symptoms.
Progesterone and Reproduction
Technically, your first trimester of pregnancy starts with the end of your last menstrual period, two weeks before you conceive. During this time, progesterone has important roles to play in preparing your body for conception. When you ovulate, specialized tissue in the ovary called the corpus luteum starts secreting the hormone progesterone. This helps prepare the lining of the uterus for implantation of a fertilized egg, explains Dr. Lauralee Sherwood in her book "Human Physiology."
After Fertilization
Once you conceive, the fertilized egg must implant in the lining of your uterus. This occurs around 10 to14 days after conception, or at nearly the end of the fourth week of pregnancy, explain Heidi Murkoff and Sharon Mazel in their book "What To Expect When You're Expecting." Normally by this time, if fertilization hadn't occurred, progesterone production would fall and you'd have a period. However, the fertilized egg secretes a hormone called human chorionic gonadotropin, or hCG, that keeps the corpus luteum producing progesterone, which maintains the lining of the uterus.
Rising Progesterone
As your embryo begins to develop in the uterus and continues to produce hCG, progesterone levels rise. This leads to some of the symptoms of early pregnancy, many of which begin around the sixth week of pregnancy, or about two weeks after your missed period. MayoClinic.com notes that one very common symptom of early pregnancy is fatigue, because rising progesterone levels can make you feel sleepy. You may also experience more headaches during early pregnancy.
Normal Progesterone Levels
Some physicians like to test progesterone levels in early pregnancy to make sure they're rising adequately, since low progesterone can cause the uterine lining to slough, which ends a pregnancy. According to the Advanced Fertility Center of Chicago, progesterone levels should be above 15 ng/mL in normal pregnancies. Levels below this may signal an ectopic, or tubal, pregnancy or may simply indicate that the corpus luteum is underproducing progesterone. In some cases, obstetricians can treat low progesterone with supplements.
Expert Insight
As your pregnancy progresses, your fetus will build a functional placenta. The placenta is an organ that the fetus makes from its own cells and that attaches to the inside of your uterine wall. Blood vessels from your body grow near placental blood vessels, and you transfer nutrients and oxygen to your baby through the placenta. The placenta produces progesterone, and eventually -- around the fourth month of pregnancy -- takes over progesterone production from the corpus luteum, which disintegrates.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008
- MayoClinic.com: Progesterone
- Advanced Fertility Institute of Chicago: Progesterone
