As many as 90 percent of pregnant women experience some nausea in early pregnancy and as many as 33 percent vomit during pregnancy. While no one really wants to feel sick through the first three months of pregnancy, you might worry that your lack of nausea indicates that something's wrong with your baby. Although nausea does indicate your pregnancy hormones levels are rising appropriately, not having morning sickness isn't necessarily a sign that something's wrong.
Definition
Morning sickness doesn't always live up to its name; you might feel nauseated when you first wake up in the morning, but for some women, morning sickness lasts all day—or night. Morning sickness generally begins around week six of pregnancy, two weeks after you miss your first period, which is a time when hormone levels are rising rapidly. Morning sickness begins to fade by week 14 to 16, when hormone levels also begin to stabilize.
Causes
Increases in hormone levels—including human chorionic gonadotropin, or hCG, produced by the placenta; progesterone, produced initially by the corpus luteum, the leftover remnant of the egg after ovulation; and estrogen, the dominant female hormone—might all contribute to morning sickness. Increases in thyroxine, a hormone produced by the thyroid gland, could also increase queasiness. Women having twins or triplets often have more severe nausea than those having one baby, which supports the theory that higher hormone levels cause morning sickness. An interesting theory about morning sickness is that nausea and vomiting may have a protective effect, expelling food that could make a mom-to-be ill or have toxic effects that could damage the fetus.
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Significance
Studies show that women who have morning sickness have a significantly reduced rate of miscarriage, preterm delivery or intrauterine growth retardation compared with women who don't experience this common pregnancy symptom. There's no definite answer to why some women who have healthy babies don't have morning sickness. Some women might be immune to the effects of rising hormones. Women who don't experience morning sickness might have hormone levels lower than others but still within normal limits. Diet might make a difference. In some cultures, morning sickness is uncommon. In cultures in which morning sickness is rare, the diet consists primarily of grain, especially corn. In cultures in which meat is eaten more frequently, morning sickness is more common.
Nausea and Vomiting as a Negative Sign
Severe nausea in pregnancy can be a sign of a problem with the pregnancy rather than a positive sign. In a pregnancy complication called hydatidiform—also called a molar pregnancy—the placental tissue grows abnormally while the fetus never develops. Since the placental tissue produces the hormone hCG, abnormal placental growth causes hCG levels to rise beyond normal pregnancy levels. As a result of the very high hCG levels, you might have very severe nausea and vomiting.
Checking Your Baby's Well-Being
While you can't peer into the uterus to see how your baby's doing, a fetal ultrasound can take a look that can put your mind at ease if you're worried about your lack of pregnancy symptoms. If you see a fetal heartbeat by six to seven weeks, your risk of miscarriage drops by 70 to 90 percent. Blood work done every few days in the first weeks of pregnancy can also show whether your hormone levels, particularly hCG, are rising. Your hCG levels normally double every two to three days in a healthy pregnancy, although there are exceptions to every rule.
Suzanne Robin is a registered nurse with more than 25 years of experience in oncology, labor/delivery, neonatal intensive care, infertility and ophthalmology. She also has extensive experience working in home health with developmentally delayed or medically fragile children. Robin received her RN degree from Western Oklahoma State College. She has coauthored and edited numerous books for the Wiley "Dummies" series.
