Ultrasounds and Tests
Throughout your pregnancy, you and your babies will go through several tests and assessments. Some are prompted by the extra risks inherent in a multiple pregnancy, requiring more intensive monitoring than a singleton pregnancy. Others are routine assessments that are recommended for all pregnancies. It's important to know what each test is measuring and how it will be performed.
Ultrasound assessments can be a very enjoyable and reassuring test for expectant parents, offering them a peek at the developing babies. There are no known risks associated with ultrasound technology, and it generates little discomfort for the mother, other than requiring her to lie flat during the procedure. You are more likely to have several ultrasounds with a multiple pregnancy, as it is a simple, inexpensive, and relatively noninvasive diagnostic tool.
Some doctors routinely perform an ultrasound on their patients during their initial office visit, about a month into the pregnancy. An early ultrasound or sonogram is often the method by which a multiple pregnancy is confirmed, and perhaps your own twins, triplets, or more were revealed in the shadowy blobs of an ultrasound image. Others recommend an ultrasound evaluation toward the end of the first trimester as part of a screening evaluation for chromosomal abnormalities. During the second trimester, a more comprehensive ultrasound can be performed to detect a wider range of issues.
The American Congress of Obstetricians and Gynecologists is somewhat wary of gratuitous ultrasound use in a healthy pregnancy; however, diagnosing and monitoring multiple pregnancy is considered acceptable and is a recommended use of the technology.
Your ultrasound scans may be performed by a trained sonographer, or by your obstetrician or perinatologist. Advances in ultrasound technology continue to provide even more detailed and defined pictures of the womb. Doppler technology, familiar to many as a weather forecasting tool, makes it possible to monitor fetal blood flow. Three-dimensional (3-D) imaging uses a computer to process a series of images into an even more detailed and defined picture of your womb, while 4-D ultrasound incorporates movement in real time, providing a very lifelike look at the developing babies.
Sometimes a Level II ultrasound is recommended for multiple pregnancies. This is simply a more detailed assessment. The same equipment is utilized, but it is generally performed by a maternal-fetal specialist at a hospital rather than in your doctor's or midwife's office. It will likely take an hour or two, whereas a regular ultrasound lasts about thirty minutes.
In the second trimester, most physicians recommend a routine ultrasound, often called a structural ultrasound. Generally, this exam is scheduled at about eighteen to twenty weeks. At this point in the pregnancy, the babies' anatomy is developed enough to be assessed, yet the babies are still small enough to be seen individually. Later in the pregnancy, as the womb becomes more crowded, their body parts may overlap and become more difficult to examine.
The procedure provides much useful information. It helps to ascertain that the babies are developing on schedule, confirms their due dates, and rules out potential problems such as Down syndrome, spina bifida, and hydrocephaly. Often other details are revealed, such as the babies' genders (if you want to make them known) and perhaps even their zygosity. In addition to getting a good look at the babies, a second trimester ultrasound is also a good time to check the length of your cervix. A long cervix is tightly closed, an encouraging sign that preterm labor is not imminent.
During the procedure, your doctor will likely spend some time trying to identify and assess the membrane that separates the babies' sac. A discernible membrane or a triangular shape called the lambda sign may indicate that the babies are dichorionic, although it doesn't necessarily confirm that they are dizygotic—even monozygotic (identical) twins can be dichorionic.) A thin membrane or a T-shape where the membrane meets the placenta might identify monochorionic twins, while the lack of a membrane might be a clue that the babies are monoamniotic.
Screening tests help to identify risks and determine follow-up treatment. There are several recommended screening tests throughout pregnancy; some are routine tests offered to all pregnant women, while others are to determine risks more likely to be encountered in a multiple pregnancy. It is important to realize that the results of screening tests don't necessarily indicate the presence of a problem or complication; rather, these tests are used to catch potential issues and will usually prompt follow-up for actual diagnosis.
In the first trimester, a sample of maternal blood is screened for chromosomal abnormalities, such as Down syndrome and trisomy 18. This screening is usually performed between the eleventh and thirteenth week of pregnancy, and may be accompanied by an ultrasound scan to measure the nuchal translucency of the tissue on the back of the fetuses' necks.
A similar screening occurs in the second trimester. The quad screen occurs between fifteen and twenty weeks, when an analysis of a blood sample measures for four substances that can indicate possible genetic disorders. Abnormal levels of AFP (alpha-fetoprotein), hCG (human chorionic gonadotropin), estriol, and inhibin-A may alert physicians to conditions such as spina bifida, anencephaly, or Down syndrome. Your medical caregiver may refer to this screening by another name. Alternative versions and combinations of this screening test may be presented as a triple screen test, multiple marker screening, Maternal Serum Alpha-Fetoprotein (MSAFP), or AFP Plus.
Late in the second trimester, you will likely be screened for gestational diabetes. The test measures the amount of glucose in your blood to determine whether pregnancy hormones have affected the way that your body processes insulin. In most cases, the glucose level is measured via a blood sample. Your doctor will provide you with a sweet, high-glucose beverage and instructions on when to drink it. About an hour later, blood will be drawn and sent to the lab. If your blood serum glucose is high, you may be at risk for gestational diabetes. Usually a second round of more intensive testing, called an oral glucose tolerance test, is prescribed. You may be required to follow a special diet for a few days or fast the night before. It can be a time-consuming test, since your blood will be drawn several times.
In a singleton pregnancy, gestational diabetes screening is usually performed early in the third trimester, but many doctors recommend earlier testing for moms of multiples. The risk of gestational diabetes is nearly doubled for moms expecting more than one baby.
Testing for Preterm Labor
Fetal fibronectin testing allows doctors to predict whether preterm labor is imminent, although it doesn't provide any guarantees unless the test provides a negative result. Fetal fibronectin (fFN) is a protein found in the membranes and fluid of the amniotic sac. A glue-like substance, it bonds the amniotic sac(s) to the lining of the uterus. It begins to break down naturally about the thirty-fifth week of pregnancy, as the body prepares to deliver. However, if its presence is detected in the area of the mother's cervix or vagina between twenty-four and thirty-four weeks' gestation, it could indicate the onset of preterm labor, even when other symptoms aren't apparent.
Fetal fibronectin testing is quick and simple, and carries no risk of side effects. A swab of secretions near the cervix is collected and analyzed in a laboratory. If a negative result is returned, your chances of delivering in the next fourteen days are low. A positive test doesn't mean that you're ready to deliver; rather, it simply alerts doctors to the possibility of the onset of preterm labor so that additional precautions can be instituted.
Your doctor or midwife may perform one or more fetal fibronectin tests in the third trimester to assess your risk of early delivery. Biweekly scans beginning at twenty-four weeks can screen for an increased risk of preterm labor and guide decisions about your medical care.
A negative fibronectin test can be reassuring; your chances of delivering preterm are less than 10 percent. A positive is less conclusive. The detection of fetal fibronectin doesn't necessarily mean that labor is imminent, but it will probably require you to be closely monitored.
During the last trimester, you're likely to have ample opportunity to keep tabs on your babies. Fetal surveillance during the last trimester is accomplished with ultrasound and heart rate monitoring, with a variety of tests that determine the babies' condition. A nonstress test is a painless way for you to participate in assessing the babies. It is performed by your doctor in the third trimester, usually at about thirty weeks. Testing is done with transducers that measure each baby's heart rate and an additional monitor to record any uterine contractions. You'll be asked to sit quietly or lie down and relax. Remember, it's called a nonstress test, so don't be anxious!
As the transducers monitor the babies' heart rates, you may be asked to indicate your experience of fetal movement. The test measures the heart rate of the baby in response to its movement to assess oxygen levels. A healthy baby's heart rate will increase with movement and decrease with rest, so the results of this test can help determine how your multiples are faring in their current womb conditions.
A nonstress test is one component of a biophysical profile, a test that gives an overall assessment of the babies' condition. It's usually recommended midway through the last trimester, beginning at about week thirty-two. It includes evaluations of each baby's heart rate activity, respiration, body movements, muscle tone, and amniotic fluid volume. It may also include an assessment of the placenta. The nonstress test provides information about the fetuses' heart rate activity, while the rest of the elements are measured via ultrasound. If one or more of the babies scores low on a biophysical profile, it may be cause for concern and may even prompt consideration of an early delivery.
Amniocentesis and CVS
Between the fourteenth and twentieth week of your pregnancy, you may be scheduled for an amniocentesis, perhaps in response to the results of a screening test. During the process of amniocentesis, or amnio, your caregiver uses an ultrasound-guided needle to withdraw fluid from the babies' amniotic sac. Analysis of the fluid sample, which contains fetal cells, provides a wealth of information about the babies.
Amniocentesis may elicit some cramping, and you'll probably be advised to take it easy after the procedure. There are some inherent risks; the needle's invasion of the uterus can trigger infection, preterm labor, or even miscarriage. In a multiple pregnancy in which each baby's amniotic sac must be sampled, the risks may be increased. Generally, this procedure is recommended for mothers over the age of thirty-five, or whose families have a history of chromosomal abnormalities or birth defects. It may also be warranted if there is an indication that you will deliver your babies prematurely, as it can be an effective tool for assessing their lung maturity.
An alternative to amniocentesis is chorionic villus sampling (CVS). It is generally performed earlier in pregnancy, in the first trimester. Chorionic villi are tiny tentacles of tissue projecting from the chorion that provide a sample of the babies' genetic material. A catheter is inserted through either the cervix or abdominal wall to extract a sample of the villi. Although it is an extremely accurate tool for detecting genetic disorders, the risk of miscarriage after CVS is even 1 to 2 percent higher than with amniocentesis. It can be a challenging procedure when there are multiples, especially if they share a placenta. Your doctor will advise you as to the risks and benefits of undergoing such testing.