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Twin Pregnancy: Prenatal Tests in the Second Trimester

By now, you know the routine. The second trimester prenatal visits are more predictable. You look forward to that special moment when you can hear the babies' heartbeats for the first time. You've likely established a comfortable relationship with your doctor, too. With twins, more frequent prenatal visits and tests might feel like a full-time job!

Routine Tests

At each doctor visit, you continue to have urine testing to check for protein and sugar and any signs of infection. The doctor or nurse checks your weight and blood pressure as well. These tests are even more important since you are at higher risk for both gestational high blood pressure and gestational diabetes. Twins also put you at greater risk for anemia. So you may have blood tests throughout your pregnancy.

More exciting are the measurement of your rapidly growing abdomen and the sounds of your babies' hearts.

  • Fundal height. At each visit, your doctor will measure the height of your uterus (fundal height). This helps verify the babies' growth. 
  • Fetal heart tones. Your doctor can probably hear two separate fetal heart tones using a handheld ultrasound device. 

Ultrasound

With ultrasound, measurements of the head and bones help confirm the gestational age and the normal growth of each baby. It is possible to tell whether one twin is much smaller than the other.

At this stage, ultrasound can confirm that you have two babies and possibly whether they are fraternal or identical. It can also confirm:

  • Placement of the placenta(s)
  • Amount of amniotic fluid
  • Babies' sex
  • There is normal anatomy

You may be able to watch the babies' tiny hearts beating! And, if you want to, you might get a peek at the babies' genital areas to find out if they are girls or boys -- or one of each.

You will continue to have ultrasounds about every three to four weeks throughout the rest of your pregnancy to check your babies' growth and measure amniotic fluid.

Blood Sugar Test

With twins, you are at increased risk for developing gestational diabetes. So you will have a glucose test early in pregnancy to check your blood sugar level. Your doctor may repeat this test later in pregnancy.

Optional Screening for Birth Defects

During your second trimester, your doctor will offer other screening for birth defects, especially if you have a family history of birth defects or are over age 35. Your doctor will suggest what's best for you, depending upon your risk factors and results from any first trimester screening. Note that doctors offer the multiple marker screen to all women, regardless of their age or risk.

Multiple marker screening.  A doctor takes a sample of your blood between the 15th and 20th weeks of pregnancy. You might hear these screenings referred to as triple screen, quadruple screen, or alpha fetoprotein (AFP) test. These tests can detect defects or levels of hormones that may indicate a possible problem. AFP levels are normally higher with twins. But very high levels can indicate neural tube defects such as spina bifida.

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