Ultrasounds allow physicians--and curious parents--the opportunity to see a developing baby while it's still in the uterus. While obstetricians can get information about a baby's growth from measuring the mother's uterus, ultrasounds allow for direct measurement, which helps ensure that growth is progressing on time. Many obstetricians perform several ultrasounds on each patient during pregnancy.
Function
The major purpose of a medically advised ultrasound is to gain information about fetal growth. Early in a woman's pregnancy, the primary purpose of an ultrasound is to locate the gestational sac, which provides evidence that the embryo has implanted in the uterus properly, note Heidi Murkoff and Sharon Mazel in their book, "What To Expect When You're Expecting." Later ultrasounds verify that the fetus is growing as expected.
Time Frame
A woman's first ultrasound typically takes place when she's approximately four weeks post-conception, or six weeks pregnant, notes Dr. Miriam Stoppard in her book, "Conception, Pregnancy and Birth." A second ultrasound may follow some time between 11 and 14 weeks of pregnancy, the purpose of which is to check for certain birth defects, including Down's Syndrome. A third, and often final, ultrasound at or around 20 weeks not only confirms growth but also often provides information about gender.
Considerations
While fetal growth ultrasounds provide much more accurate information about growth than an obstetrician can obtain by palpating the uterus through the abdomen, ultrasounds aren't infallible. Early ultrasounds help obstetricians "date" a pregnancy--that is, predict a due date--and while they're typically accurate within about a week or two, small differences in fetal growth rates can cause babies to appear younger or older than they actually are. Still, notes Dr. Raymond Poliakin in his book, "What You Didn't Think To Ask Your Obstetrician," early ultrasounds remain the most accurate method of dating a pregnancy.
Logistics
Fetal growth ultrasounds typically happen in one of two ways, notes Dr. Stoppard. Early ultrasounds, meaning those that take place before the uterus has risen above a woman's pubic bone, require the ultrasound technician to use a wand inserted in the vagina in order to visualize the fetus. Later on, technicians use transabdominal ultrasound probes, though women in their first and early second trimesters often need to have full bladders in order to lift the uterus into the abdomen. Late in pregnancy, the fetus is easily visualized transabdominally without a full bladder.
Warning
Many women find it so reassuring to see that their baby is growing properly on an ultrasound that they seek out extra ultrasounds during the pregnancy. "Boutique" ultrasound providers, meaning those that offer ultrasounds outside a doctor's office and without medical cause, afford parents the opportunity to see their baby as many times as they like. Still, notes Dr. Poliakin, the American College of Obstetrics and Gynecology recommends that parents avoid boutique providers, since the effects of unnecessary and non-medical ultrasounds aren't well-known.
References
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008.
- "Conception, Pregnancy and Birth"; Miriam Stoppard, M.D.; 2008.
- "What You Didn't Think to Ask Your Obstetrician"; Raymond Poliakin, M.D.; 2007.
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