Ultrasound: A Trimester-by-Trimester Guide

Second Trimester

pregnant couple getting ultrasound

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.

 

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