One of the most common early symptoms of pregnancy is morning sickness. Pregnant women often begin experiencing it as early as a few weeks after conception, and it typically lasts until near the end of the first trimester. Your hormones, including progesterone, are to blame for the nausea and queasiness so common in early pregnancy.
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When you become pregnant, your normal hormonal cycles change significantly. Instead of estrogen and progesterone levels rising and then falling each month, you experience nine months of high estrogen and progesterone, plus high levels of a third hormone, called hCG, or human chorionic gonadotropin. These hormones work together to produce the necessary changes of pregnancy, including helping to maintain the uterine lining, which is where your developing baby implants within just a week or two of fertilization.
The specific role of progesterone relates directly to the uterine lining, and indirectly to other body systems. Until your baby develops the placenta, an organ that typically reaches completion around the fourth month of pregnancy, it's entirely dependent upon the blood vessels of the uterine lining for nutrients and oxygen. Progesterone helps maintain the uterine lining, and without high progesterone, you can't maintain an early pregnancy, explains Dr. Lauralee Sherwood in her book "Human Physiology."
One of the most troublesome of the effects of high progesterone is that it contributes to slowing of the digestive tract. This helps you extract all the nutrients from the food you eat, but it also keeps food in the gut longer, and can increase your risk of nausea, especially when your blood sugar drops. Heidi Murkoff and Sharon Mazel, in their book "What To Expect When You're Expecting," note that morning sickness occurs due to both the actions of the hormones hCG and progesterone upon the gut.
Since morning sickness is often at its worst when your blood sugar is low, Dr. Miriam Stoppard, in her book "Conception, Pregnancy and Birth," recommends many smaller meals each day to help maintain your blood sugar. Combining protein-rich foods like cheese or eggs with carbohydrate foods like crackers can help keep your blood sugar more stable than consuming carbohydrate alone. Further, small meals help keep your gut operating more regularly than larger meals.
While most obstetricians don't recommend pharmaceuticals during pregnancy, you can help alleviate the symptoms of morning sickness until such time as your body becomes accustomed to the excess progesterone, which generally occurs around the third month of pregnancy. Eating ginger candy or drinking ginger tea can help, note Murkoff and Mazel, as can having a small snack before you get out of bed in the morning.