Pregnancy
Routine Checkups
If you think you might be pregnant, you can use a home pregnancy test as soon as the first day of your first missed menstrual period. Pregnancy is measured in weeks from the first day of your last menstrual period (LMP). There are several ways to calculate how long you have been pregnant. You can also use your LMP to calculate your due date
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As soon as you know you're pregnant, make an appointment with your doctor or certified nurse-midwife (CNM). Your first prenatal visit will provide information that can be used to check for any problems as your pregnancy progresses.
Good care during pregnancy includes regularly scheduled prenatal exams. At each prenatal visit, you'll be weighed, have your abdomen measured, and have your blood pressure and urine checked. Use this time to discuss your list of pregnancy concerns or problems with your health professional. At different times in your pregnancy, you will have additional exams and tests performed. Although some are routine, others are only done when a problem is suspected or if you have a risk factor for a problem.
First prenatal visit exams and tests include a health history, physical examination, and blood and urine tests.
First-trimester exams and tests may include fetal ultrasound, which uses reflected sound waves to provide an image of your fetus and placenta. The late first trimester is the earliest time when you can have the newer, noninvasive Down syndrome screening using a blood test and an ultrasound measurement of fetal neck (nuchal fold) thickness. (Nuchal fold ultrasound is not yet widely available, because only a specially trained provider can do it.) This is also when you can have genetic testing of your placenta (chorionic villus sampling, or CVS). A CVS gives you earlier results than a second-trimester amniocentesis. Only a highly trained provider can do a CVS.
Second-trimester exams and tests may include fetal ultrasound and electronic fetal heart monitoring. In the early second trimester, you can have the triple or quadruple screen. This screen measures your blood levels of:
- Alpha-fetoprotein (AFP).
- Human chorionic gonadotropin (hCG).
- Estrogen (estriol).
- Inhibin A (quad screen only).
If you are at risk for genetic problems or your triple or quad screen says your fetus might have a problem, you may have testing of the fluid surrounding your baby (amniocentesis). Later on in the second trimester, you will have an oral glucose screen for possible gestational diabetes.
If you have Rh negative blood, you may have an antibody screen and will receive an injection of Rh immune globulin.
Third-trimester exams and tests may include fetal ultrasound, hepatitis B, and group B strep screening.
All pregnant women should be screened for human immunodeficiency virus (HIV) infection to help prevent newborn HIV infection.4 Some health professionals may not order this test unless you request it.
Deciding about birth defect testing
Talk to your doctor or nurse-midwife about screening for birth defects in your fetus. You can choose from different kinds of tests. If you are worried about birth defect risk, you might want test results as early as possible. If your risk for having a baby with a birth defect is very low, you may decide to have no testing. On the other hand, if knowing early would not change how you handle the pregnancy in any way, you might decide against earlier testing, or testing at all. It's your decision.
A screening test uses your blood sample and/or an ultrasound to look at the chance that your fetus might have a problem. In some medical centers, you can be screened in the late first trimester for possible Down syndrome using a nuchal ultrasound and blood tests. (Only a specially trained provider can do this type of ultrasound, and is not widely available.) You can be screened in the earlier second trimester for possible birth defects such as Down syndrome or a neural tube defect with a blood test called the triple or quadruple screen. These tests are not risky for you or your fetus.
A diagnostic test detects actual problems. If your screening results suggest a higher-than-average chance of a fetal problem, you can then decide whether to have a chorionic villus sampling or an amniocentesis. Or if you already know you are higher-risk for a birth defect, because of your age or family history, you might decide not to have the screening and go straight to diagnostic testing. A key factor for you to know is that chorionic villus sampling and amniocentesis have slight risks of miscarriage.
For more information about how your fetus is changing this month, and about what tests you might think about having, see Interactive Tool: From Embryo to Baby in 9 Months
What to Think About
Timing is an important consideration when deciding which type of genetic testing to have.
- CVS can be done earlier in pregnancy (usually at 10 to 12 weeks) than amniocentesis (usually at about 16 weeks).5 This allows you to make an earlier decision about whether to continue or end the pregnancy. Results of CVS may be available more quickly (within several days) than amniocentesis results (2 weeks).
- CVS doesn't detect neural tube defects, so an alpha-fetoprotein test, part of the triple screen, is recommended along with it. Ideally, this is done at 16 to 18 weeks.5
- Both CVS and amniocentesis pose a slight chance of causing a miscarriage because they disturb the uterus, amniotic sac, and/or placenta. One recent study showed that the miscarriage risk for either test was about 1 in 400 when done by a highly trained provider.6 Some studies have shown higher miscarriage risks, between 2 and 4 in 400. 7 This greater risk may be more likely in medical centers with less experienced providers, especially for CVS. (The risk of miscarriage with CVS may be smaller when the procedure is done through the abdomen than when it is done through the cervix.8)
For more information, see the following:
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| Author: | Shannon Erstad, MBA/MPH | Last Updated: November 30, 2006 |
| Medical Review: | Renée M. Crichlow, MD - Family Medicine Kirtly Jones, MD - Obstetrics and Gynecology | |
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