18 Weeks Pregnant: Understanding Prenatal Tests

18 Weeks Pregnant

In this article

• Pregnancy Week 18: All About You
• Pregnancy Week 18: All About Baby
• How Big Is Baby?
• Most Common Pregnancy Questions
• Multiple Madness
• For Your Partner
• Fun Fact

Wondering what's going on with all the prenatal tests your healthcare provider is ordering? Find answers here.

Did you know that studies have shown that a full 60 percent of all expectant fathers show some symptoms of pregnancy? They may experience nausea, mood swings, weight gain, and odd cravings.

Pregnancy Week 18: All About You

By now you're feeling your baby-to-be wiggle inside you. The excitement surrounding her first movements will probably help you forget some of your pregnancy woes. As your tummy continues to expand you may notice stretch marks and have itchy skin. Your back will ache as your body adjusts to its new alignment. Thankfully, nausea is mostly likely a distant memory.

Understanding Pregnancy Tests
Between your sixteenth and twentieth weeks of pregnancy you'll be offered a series of tests to determine if your baby-to-be is at risk for certain genetic problems. Notice that these tests are offered but not required. Before you submit to the tests, it's important to understand what each entails and what the results will tell you about your developing baby.

Risk Assessments, Not Tests
Rather than view genetic tests as pass/fail, physicians see them as risk assessments, looking at whether your baby-to-be has a greater risk for certain genetic problems. For instance, a "positive" result doesn't necessarily indicate a problem with your baby, but that you might consider additional—and more definitive testing—to determine your baby's health. "The way I describe it to my patients is that these tests are like casting a wide net," explains Dr. Joanne Motino Bailey, PhD, a certified nurse midwife and a professor of women's studies at the University of Michigan. "You have plenty of healthy babies that are caught in the net" along with a handful of babies with genetic concerns.

Non-Invasive Tests
The main reason for so many false positives, according to Dr. Motino Bailey, is that physicians want to offer the safest, most non-invasive way to test your unborn baby for certain genetic disorders. These tests involve a simple blood test with virtually no risk to your baby-to-be.

• Quad test/triple screen: Your healthcare provider will draw your blood and test it for elevated levels of certain hormones and proteins, which may indicate your unborn baby has a genetic problem. The quad tests for Down syndrome, spina bifida, and other genetic problems. Keep in mind that this test has a high false positive and a high false negative rate.
Depending on your healthcare provider, you may be offered the triple screen, which includes looking at two hormone levels and one protein, or the quad test (quickly becoming the norm), which tests for an additional protein that may indicate genetic problems.
• Nuchal translucency screening (NTS): A more recent test option combines a blood test with an ultrasound to look for risk factors that may indicate that your unborn baby has Down syndrome. The test is highly specialized, however, so it may not be available in your area.
• Cystic fibrosis: Your blood sample will also be tested for cystic fibrosis. The test will determine if you are a CF carrier. If you are, your partner may then be tested. Because this is a recessive disorder, both you and your partner must be carriers for your unborn baby to be at risk. If both parents are carriers, according to ACOG, your unborn baby has a one in four chance of developing the disease.
• Ethnicity-based blood tests: Certain genetic disorders tend to appear in certain ethnicities. Your physician will ask a series of questions about your background to determine whether these tests are necessary for you.

Invasive Tests

If your first round of screening comes back with positive results (again, not meaning that your baby has a problem, but that she might be at a risk) you will be offered additional tests to give you a definitive answer about your unborn baby's genetic makeup. While these tests offer the yes/no answers you may be looking for, they do carry a risk of miscarriage.

• Amniocentesis: With an amnio, your healthcare provider inserts a long needle through your abdomen and into the uterus to collect a small sample of amniotic fluid. The fluid is then tested for genetic problems, such as Down syndrome, neural tube defects, and other disorders. The test is done between pregnancy weeks 16 and 20.
• Chorionic villus sampling (CVS): In CVS, a needle placed through your abdomen or through your vagina withdraws a tiny portion of the placenta. The sample can then be tested for Down syndrome, sickle-cell anemia, and cystic fibrosis. The test is performed between pregnancy weeks 10 and 12.

Note: CVS, a first-trimester test, provides parents with an earlier diagnosis than amniocentesis, a second-trimester test. Until recently, CVS had been associated with a slightly higher rate of miscarriage, but findings published in the September 2006 issue of Obstetrics & Gynecology show that the miscarriage rate is actually the same for both CVS and amnio, below two percent.

These tests are not to be taken lightly, advises Dr. Bailey. Take time to ask your healthcare provider about each test.

Pregnancy Week 18: All About Baby

At week 18, your baby-to-be's senses are maturing. She's able to hear sounds within her own comfortable environment, such as the sound of your heart beating, as well as external sounds, such as your voice. She may become more active for certain sounds, and you'll feel her movements. At this point in her development she's still small enough that she has plenty of room to wiggle.

How Big Is Baby?

Your little one is about 6 ounces and 5 to 6 inches long (crown to rump). Baby is about the size of a grapefruit.

Most Common Pregnancy Questions

Now that I know the sex of my baby, should I be doing anything differently?
There has been a lot in the news about phytoestrogens being a problem with women who are dealing with infertility and also report of lavender oils causing temporary increase in breast tissue (gynecomastia) for boys. Foods high in phytoestrogens (soy beans, tofu, tempeh, soy beverages, flax, sesame seeds) are those whose effects may mimic estrogen. Phytoestrogens act like weakened estrogen. There are some studies that hypothesize that these foods can affect infertility in women and in some cases men. One study, published in the January 2000 issue of The British Journal of Urology points out the possible correlation in the increased occurrence of hypospadius (the opening to the penis instead of being located at the tip of the penis may be on the underside). This increase is noted in babies of women who consume more phytoestrogens in a vegetarian diet.

When researchers look at the effects of diets high in soy as it relates to infertility, the studies done within labs with mice and rats involved ingestion of very large quantities. The quantities used in research were higher than what most women, even those who eat diets high in foods containing phytoestrogens, would normally consume.

How does all this relate to your pregnancy? The tried-and-true practice of everything in moderation is really the best approach here. Eating too much of one type of food can lead to not having enough room to eat other things that you need. So eat a colorful, varied diet. Take in a balance of fruits, veggies, grains, proteins, and fats. Talk to your doctor or a dietitian if you'd like help planning a healthy pregnancy diet.

Once your baby boy is born, talk with your pediatrician about the use of lavender oils or bath. There are boys who have experienced an increase in breast tissue after using lavender products, but this was only temporary (the tissue went back to its normal size after discontinuing use of the lavender).

Multiple Madness

Prepping the Nursery (Times Two!)
A woman expecting a singleton may not begin to decorate the nursery until she is at least 24 weeks along in her pregnancy. But when expecting multiples, it's important to get the nursery ready earlier rather than later. You simply have no way of knowing if, or when, you might be relegated to bed rest or restricted activity. Should that happen, you certainly don't want to be panicked over an unfinished nursery.

If your babies do arrive before the nursery is finished, it's not the end of the world. Your twins may spend some time in the neonatal intensive care unit, which will give you extra days to prepare. Also, your new little ones can always sleep in your room for the first few days or weeks. (With a crib or Pack 'n Play, babies can sleep anywhere).

Don't stress out too much about decorating your babies' room. For the first few months, the wall borders and other decorative touches are more for you than for the babies; they can barely see them!

However, to alleviate undo stress, it is a good idea to get together your nursery furniture and establish a general theme. Also, purchase your bouncy seats or portable cribs/playards so you have somewhere safe to put the babies when they aren't in their crib(s) or your arms. Have a few packages of newborn and size one diapers on hand and a few sets of comfortable clothing for each baby.

There aren't yet larger cribs designed for twins, and the philosophies on keeping twins in the same crib are mixed, for both medical and psychological reasons (that's a separate article to itself!) Logistically, keeping your twins in one room is tricky: there's often not space for more than twins cribs, one dresser, and a rocking chair. This is where planning ahead can help. Map out the room and try different furniture configurations before your babies come.

It's a good idea to maintain a checklist of things you need. Should the babies come early, your husband or another relative or friend can take that checklist to the store and purchase any necessities you missed before you and the babies come home.

For Your Partner

Beginning to Build Your Bond
As a dad-to-be, you don't have the same connection to your baby as your partner does. If you're looking for a fun way to build a connection with your unborn child, one of the best ways to get started is to talk to or read to your baby.

You might think talking to your partner's belly is a little embarrassing. Don't! Reading to baby can become a very special time between you and your partner; a new form of intimacy and sharing (and some quiet time that will be harder to come by after your baby is born).

But maybe even more importantly, reading to your unborn baby helps you relate to your baby as a person, giving you a head start for when your little one arrives in person.

In addition, your baby can now hear sounds and voices from the womb. This means you have a unique opportunity to help your little baby begin to recognize your own voice. Of course, your baby has a good chance of recognizing your partner's voice because she is with your baby all of the time. Reading, talking, and singing are all ways to share your voice with your baby.

After my twins were born, I stood next to my daughter in the hospital and called her name … and she turned her head to me, confirming all the time I had spent communicating with her while she was in the womb was worth it.

Fun Fact

All of your organs are working hard to help your baby-to-be develop, but perhaps the hardest working organ during pregnancy is your heart. Your blood volume increases by 50 percent during your pregnancy, meaning your heart has to work that much harder to pump the blood throughout your body.

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