Blood Work

You won't be handing out your blood as frequently as your urine, but there are still a few blood tests involved in pregnancy.

Hemoglobin Count

Your hemoglobin levels, the red blood cells that carry oxygen throughout your body, will be assessed at your initial prenatal visit and may be tested again in the second and third trimesters. Low hemoglobin levels (called anemia) occur frequently in pregnancy due to the vast boost of your total blood volume product. Levels that are too low can be a risk factor for low birth weight babies. If your total hemoglobin levels are below 12 mg/dL, your provider may prescribe iron supplements to build your hemoglobin reserves and order regular hemoglobin screenings at each prenatal visit to monitor your progress.

Glucose Challenge Test (1°GCT)

The glucose challenge test is a screening tool for gestational diabetes mellitus (GDM). It's typically given between weeks 24 and 28 of pregnancy but may be administered earlier in women considered at high risk for GDM. If you are a woman under the age of twenty-five and have no risk factors for developing gestational diabetes, your health care provider may suggest foregoing the glucose challenge. Risk factors for GDM include having a body mass index of twenty-six or higher, being a member of a racial or ethnic group with a high prevalence of diabetes (that is, African-American, Asian-American, Hispanic, Native American, or Pacific Islander), a history of GDM or abnormal glucose tolerance, a history of delivering a large baby, advanced maternal age, or a first-degree relative with diabetes.

High blood pressure (hypertension) increases the volume of fluid in the bloodstream, and the kidneys must work double time to clean and filter the blood. Eventually, skyrocketing blood pressure threatens to damage the nephrons (filtering units of the kidneys) and blood pressure rises further because the kidneys can't keep up. (See Appendix A to learn the warning signs of hypertension.)

You will not need to fast before the one-hour fasting glucose test. The test requires you to drink fifty grams of a glucose solution, a sugary flavored drink usually called Glucola. One hour later, blood will be drawn and your blood serum glucose levels will be measured. A level of 130 mg/dL or higher is considered high. Some medical providers use a cutoff point of 140 mg/dL (ACOG endorses either). If your results exceed the guidelines your doctor has established, further testing will be necessary.

Glucose Tolerance Test (3°GTT)

Women who test with high serum glucose levels after the one-hour glucose challenge test are then given a three-hour glucose tolerance test (3°GTT) to yield a definitive diagnosis of gestational diabetes. The 3°GTT is a fasting test. You will be instructed not to eat after a certain time before taking it (usually midnight the evening before). Since pregnancy and fasting don't mix too well, especially if morning sickness is a problem, the test is typically administered first thing in the morning.

When you arrive at the lab, you will be given 100 grams of Glucola to drink. If the fasting didn't make you sick, it's likely this might. Your blood will be drawn at one-hour intervals until you reach the three-hour mark. The glucose levels in the blood samples you provide will be analyzed and checked against the diagnostic criteria for GDM.

Some women find that their queasy stomachs simply can't tolerate Glucola — the sugary drink given for gestational diabetes screening. Two separate clinical studies published in the American Journal of Obstetrics and Gynecology have shown that a tastier alternative — jelly beans — are an effective stand-in for Glucola for women who experience side effects with the glucose solution.

The American Diabetes Association recommends lab values known as the Carpenter and Coustan scale for interpreting 3°GTT results. Your health care provider may also use a second set of lab values established by the National Diabetes Data Group. Both of these are endorsed by the ACOG; the lab values that indicate a diagnosis of gestational diabetes are listed below.

<tgroup cols="3"> <colspec align="left" colnum="1" colname="col1" colwidth="20%" rowsep="0" colsep="0"/> <colspec align="left" colnum="2" colname="col2" colwidth="40%" rowsep="0" colsep="0"/> <colspec align="left" colnum="3" colname="col3" colwidth="40%" rowsep="0" colsep="0"/> <thead> <tr> <entry valign="top"><p>Blood Sample</p></td> <td><p>National Diabetes Data Group</p></td> <td><p>Carpenter and Coustan</p></td> </tr> </thead> <tbody> <tr> <td><p>Fasting</p></td> <td><p>≥=105 mg/dL</p></td> <td><p>≥=95 mg/dL</p></td> </tr> <tr> <td><p>One-hour</p></td> <td><p>≥=190 mg/dl</p></td> <td><p>≥=180 mg/dl</p></td> </tr> <tr> <td><p>Two-hour</p></td> <td><p>≥=165 mg/dl</p></td> <td><p>≥=155 mg/dl</p></td> </tr> <tr> <td><p>Three-hour</p></td> <td><p>≥=145 mg/dl</p></td> <td><p>≥=140 mg/dl</p></td> </tr> <tr> <td><p><emphasis>NOTE: GDM is diagnosed when two or more of these values are met or exceeded.</emphasis></p></td> <td><para/></td> <td><para/></td> </tr> </tbody> </tgroup> </table> <h2>Other Blood Tests</h2> <p>Your blood type and rhesus (or Rh) factor will be determined at your first prenatal visit. An Rh factor is either positive or negative. If your Rh is positive, no treatment is necessary. If you are Rh negative and your partner is Rh positive, you are at risk for Rh incompatibility with the blood type of your baby. Rh incompatibility can occur when your unborn baby is Rh positive. If some of the baby's blood enters your bloodstream, your body may produce antibodies against the baby's blood, causing her to have severe anemia. When this happens, your immune system may try to fight off the baby as an intruder, causing serious complications. If caught early on, however, the disorder can be treated effectively later in pregnancy.</p> <div class="npsb"> <div class="npmo"><img src=""></div> <p>According to the March of Dimes, one in 2,000 women will develop chickenpox during pregnancy. This virus, known clinically as varicella, has the potential to cause birth defects if it is contracted during pregnancy. Fortunately, there are tests available to determine immunity to varicella, which may be given at the first prenatal appointment if you are unsure whether you have ever had the illness. (See Chapter 8 for more information.)</p> </div> <div class="npmo"> <img src=""> </div> <div class="npmo"> <img src=""> </div> <div class="npmo"> <img src=""> </div> <div class="npmo"> <img src=""> </div> <div class="npmo"> <img src=""> </div> <div class="npmo"> <img src=""> </div> <p>Blood tests also determine whether or not you are immune to German measles (rubella). German measles can cause birth defects, especially if you contract the infection during the first trimester, and can cause cataracts, heart defects, and deafness in offspring. A majority of women have been exposed to the rubella virus or have been vaccinated against it before becoming pregnant. If you are not immune, you may be vaccinated following delivery of the baby. Some women will not have immunity despite prior vaccination.</p> <p>An HIV, hepatitis B, and syphilis test may also be done on your blood. For more on the testing of sexually transmitted infections (STIs), see the upcoming subsection on “Swabs and Smears: Sexually Transmitted Infections” in this chapter. Medications for HIV taken during pregnancy can decrease viral loads and practically eliminate transmission to the fetus in many cases. Treatment for syphilis can also prevent transmission to the fetus. If you test positive for hepatitis B, your baby will be vaccinated shortly after birth to protect him from the effects of hepatitis.</p> <p>The ACOG now recommends that all pregnant couples, regardless of ethnic background, be offered cystic fibrosis screening. Prior to 2001, only individuals with risk factors for passing along the disease, such as having parents of European (or Ashkenazi) Jewish descent, were typically offered screening. Cystic fibrosis screening is performed on either a blood or saliva sample.</p> <p>Blood tests can also screen for inherited anemia in at-risk populations. For example, couples of African, Caribbean, Eastern Mediterranean, Middle Eastern, and Asian descent are at risk for sickle cell anemia. Families of Greek, Italian, Turkish, African, West Indian, Arabian, or Asian descent may be screened for the thalassemia trait; if both father and mother are carriers, there is a chance that the fetus could develop the blood disease called thalassemia major.</p> <p>The alpha-fetoprotein (AFP) test, usually part of a larger test called the triple or quad screen,. is another blood test used in pregnancy to screen for genetic problems and certain birth defects. (Jump ahead to “Alpha-fetoprotein (AFP)/Triple or Quad Screen Test” later in this chapter for more details.)</p> <p>If initial blood screening tests for genetic conditions are positive, further testing may help determine if a trait has been passed on to the baby. A trip to a genetic counselor to weigh all your options and assess their risk and benefits is a good idea.</p> <!--/gc--> <div id="pagination"><ul><li class="prev"><a href="" title="Urine Tests">Urine Tests</a></li><li class="next"><a href="" title="Swabs and Smears">Swabs and Smears</a> </li></ul></div></div> <div id="coda"> <div id="rel"><div class="n5">Related Articles</div><ul> <li><a href="" zT="18/1YL/Zn"> Blood Work - Pregnancy </a></li> <li><a href="" zT="18/1YL/Zn"> Gestational Diabetes - Pregnancy Nutrition </a></li> <li><a href="" zT="18/1YL/Zn"> Common Tests - Pregnancy Organizer </a></li> <li><a href="" zT="18/1YL/Zn"> Blood Tests - Pregnancy Over 35 </a></li> <li><a href="" zT="18/1YL/Zn"> Diabetes, Your Baby, and You - Diabetes </a></li> </ul></div> <div id="sec"><div class="n5">Read More Diagnostic Tests and Screening</div><ul><ul class="col1"><li ><a href="">The Basics</a></li> <li ><a href="">Urine Tests</a></li> <li class="btO">Blood Work</li> <li ><a href="">Swabs and Smears</a></li> <li ><a href="">Ultrasounds</a></li> <li ><a href="">Alpha-fetoprotein (AFP)/Triple or Quad Screen Test</a></li> <li ><a href="">Amniocentesis</a></li> </ul><ul class="col2"><li ><a href="">Chorionic Villus Sampling (CVS)</a></li> <li ><a href="">Fetal Monitoring</a></li> <li ><a href="">Stress and Nonstress Test (NST)</a></li> <li ><a href="">Biophysical Profile (BPP)</a></li> <li ><a href="">Genetic Counseling</a></li> <li ><a href="">Chronic Health Conditions</a></li> </ul></ul></div> </div> <script>if(zSbL<1)zSbL=3;zSB(2);zSbL=0</script> <script>document.write('<div id="coda" class="dcl"><p class="n5">Disclaimer</p><p>Information published in 2007. 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