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Ultrasound: A Trimester-by-Trimester Guide

prenatal testing

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Relax -- You don't have to brace for needles when you get this painless test. During an ultrasound your doctor or a skilled technician uses a plastic transducer to transmit high-frequency sound waves through your uterus. These sound waves send signals back to a machine that converts them into images of your baby.

The standard ultrasound arms your doctor with valuable information. It allows him to monitor your baby's growth and track milestones, detect abnormalities, home in on your due date, determine whether you're carrying multiples, see the position of your placenta (important for delivery), and (a big one for parents-to-be!) make out the sex of your baby.

Another exam that utilizes ultrasound is Doppler fetal monitoring. This test is typically performed during the last trimester on women who suffer from gestational diabetes. A regular ultrasound uses sound waves to produce images; this one bounces high-frequency sound waves off circulating red blood cells to measure blood flow and blood pressure. The test will determine if Baby is getting enough blood.

An ultrasound is considered safe for both you and your baby when it's used for medical purposes. A trained professional who can interpret the results with accuracy and who is a pro at detecting abnormalities should perform it. Your technician should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine. Unlike X-rays, an ultrasound involves no radiation.

You missed your period. Your breasts are sore and you're exhausted. You take a home pregnancy test and a plus sign appears. Hurray! You're pregnant! Time to get "official" confirmation at the ob-gyn's office with a blood test and an ultrasound exam.

What to expect at your exam
Your first ultrasound, also known as a sonogram, will take place when you're around 6 to 8 weeks pregnant. When you schedule your appointment, be sure to ask whether you need a full bladder for the test. Sound waves travel better through liquid, so a full bladder can enhance the quality of your ultrasound. As your uterus and the fetus grow (and you have more amniotic fluid), a full bladder matters less.

At this stage, your baby is very small and your uterus and fallopian tubes are closer to your birth canal than to your abdomen, so your ob-gyn will conduct the test transvaginally to get a clearer picture. The test is painless. Your ob-gyn will place a thin, wand-like transducer probe, which transmits high-frequency sound waves through your uterus, in your vagina. The sound waves bounce off the fetus and send signals back to a machine that converts these reflections into a black and white image of your baby. It will be hard to see much in this first snapshot, but a clearer photo will come around 13 weeks, which is the ideal time to share your exciting news.

Why it's important
Your ob-gyn listens for your baby's heartbeat and estimates his age by measuring his length from head to bottom; the baby is tiny in the first trimester and is growing about a millimeter a day. From this test, your doctor will be able to determine a more accurate due date and track milestones during your pregnancy. Your ob-gyn will also rule out a tubal (ectopic) pregnancy, which is when the fetus grows in the fallopian tube instead of the uterus. (Don't worry: This occurs only 1 percent of the time.) And your doctor will also be able to tell if you're pregnant with multiples.

Other tests
All pregnant women are offered a nuchal translucency (NT) test, performed between 11 and 13 weeks, and this involves another ultrasound. The NT evaluates your risk of having a baby with Down syndrome, trisomy 18 (another chromosomal abnormality), or certain heart defects. In this two-part exam, a blood test measures levels of certain hormones and proteins in your body, and an ultrasound determines the thickness at the back of baby's neck (increased thickness indicates that he may be at risk for birth defects such as Down syndrome and trisomy 18).

At this stage, your ultrasound will likely be done on your abdomen. While you're reclining on an exam table, the doctor or ultrasound technician will slather gel on your belly, and then glide a plastic transducer over it. The test doesn't hurt, although the gel may feel cold and be messy. Wear two-piece clothing to your ultrasound, to allow for easy access to your tummy.

At some high-tech centers, doctors use 3-D ultrasound to provide pictures of the baby with photograph-quality details. High-tech centers may use this type of ultrasound to better evaluate a baby's growth and development, as well as detect facial abnormalities or neural tube defects.

Safety info
An ultrasound is considered safe for both you and your baby when it's used for medical purposes. A trained professional who can interpret the results with accuracy and who is a pro at detecting abnormalities should perform it. Your technician should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine. Experts discourage getting 3-D and 4-D (moving picture) ultrasounds at fetal portrait studios in places like shopping malls, where untrained personnel may give out inaccurate information.

 
pregnant couple getting ultrasound

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The middle of your pregnancy is thrilling for many reasons: You're halfway there! You really look pregnant (and not just like you've been noshing on too many bagels). And you're due for a detailed ultrasound, generally between weeks 18 to 20 of pregnancy, which will give you a good, long look at your baby.

What to expect at your exam
This ultrasound, called an anatomy scan, lasts 20 to 45 minutes if you're having one baby, longer if you're having multiples. Your ob-gyn uses it to assess the baby's growth and make sure all of her organs are developing properly. You'll be able to see your baby's developing body in great detail, but it can be hard for an untrained eye to distinguish the kidneys from the stomach. Ask your doctor or tech can point out organs to you as she reads the scan.

While you're reclining on an exam table, the doctor or ultrasound technician slathers gel on your abdomen, and then glides a plastic transducer over your belly. The transducer transmits high-frequency sound waves through your uterus. They bounce off the fetus, sending signals back to a machine that converts these reflections into a black and white image of your future babe. It's emotional experience to see your child up there on the TV screen.

The test doesn't hurt, although, again, the gel may feel cold and be messy. Wear two-piece clothing to your ultrasound, to allow for easy access to your tummy (you'll get a towel afterward so you can wipe off the gel).

Why it's important
This is the most thorough checkup your baby will have before she is born. The doctor will check your baby's heart rate and look for abnormalities in her brain, heart, kidneys, and liver. She'll count your baby's fingers and toes, check for birth defects, examine the placenta, and measure the amniotic fluid level. And she'll probably be able to determine your sweet pea's sex, although it's not a slam dunk; an experienced tech gets it right more than 95 percent of the time. (If you don't want to know your baby's sex, let her know ahead of time.) You might even get a 3-D view, which will offer a true-to-life glimpse of your baby's nose and bone structure. (Don't worry -- when she arrives she'll be cuter than the alien-like image she presents on the TV screen!)

Other tests
Between 14 and 20 weeks, you may have an amniocentesis to check for Down syndrome. Women whose screening test revealed a potential problem, who are 35 or older, or who have a family history of certain birth defects should consider an amniocentesis. In this procedure, a needle is inserted through your belly and into your uterus to take a sample of amniotic fluid, and your health care provider may use ultrasound to guide the placement of the needle. There's a very small (.5 percent) risk of miscarriage.

Safety info
An ultrasound is considered safe for both you and your baby when it's used for medical purposes. A trained professional who can interpret the results with accuracy and who is a pro at detecting abnormalities should perform it. Your technician should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine. Experts discourage getting 3-D and 4-D (moving picture) ultrasounds at fetal portrait studios in places like shopping malls, where untrained personnel may give out inaccurate information.

 
prenatal checkup

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For many pregnant women, their last ultrasound takes place at their 20-week anatomy scan. If you've gone past your due date, your doctor may want to keep a close eye on your baby with fetal heart-rate monitoring and ultrasounds to assess the amniotic fluid levels. Other reasons for third-trimester ultrasounds include concerns about the health of the placenta and questions about whether your baby's growth is on track. Just think of those sessions as time spent getting to know your baby. Soon enough, you'll be looking right in his baby blues.

What to expect at your exam
Earlier in your pregnancy, your doctor may have asked you to hold off on peeing before your scan. Sound waves travel better through liquid, so a full bladder can enhance the quality of your ultrasound. Now that your uterus and the fetus are larger (and you have more amniotic fluid), a full bladder matters less. When you schedule your exam, ask your doctor about this issue.

Why it's important
Many moms-to-be don't need an ultrasound in the third trimester, but if you're over age 35 or your doctor wants to closely monitor your baby's growth, you may get one or more before baby is born. (Other reasons for third-trimester ultrasounds include low levels of amniotic fluid, bleeding, and pre-term contractions.) You'll also get a follow up scan if your cervix was covered by the placenta at your 20-week scan. In 95 percent of cases the placenta moves away from your cervix by your due date, but if yours is still covering the placenta (this is called placenta previa), your ob-gyn may recommend a cesarean section (C-section) delivery.

Other tests
If you suffer from gestational diabetes, your doctor may scan you with a Doppler ultrasound in the last weeks. A regular ultrasound uses sound waves to produce images; this one bounces high-frequency sound waves off circulating red blood cells to measure blood flow and blood pressure. The test will determine if Baby is getting enough blood.

Safety info
Ultrasounds are considered safe for both you and your baby when used for medical purposes. A trained professional who can interpret the results with accuracy and is a pro at detecting abnormalities should perform it. Your tech should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine. Experts discourage getting 3-D and 4-D (moving picture) ultrasounds at fetal portrait studios in places like shopping malls, where untrained personnel may give out inaccurate information.

 

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