Second-trimester exams and tests

Routine exams and tests

At each prenatal visit, you can expect to be weighed and have your urine and blood pressure checked. Your health professional will monitor your fetus's growth and position by measuring the size of your uterus (fundal height) and gently pressing (palpating) your abdomen. Up to the 36th week of pregnancy, your fetus can regularly change position, varying from head down (vertex lie) to feet down (breech lie) or even sideways (transverse lie).

During your second trimester, expect the following routine tests:

• Glucose tolerance test (GTT), usually between the 24th and 28th weeks of pregnancy, monitors for gestational diabetes.
• Maternal serum triple or quadruple screen for birth defects is offered to all pregnant women in some states but only to higher-risk women in other states. It is done between weeks 15 and 20 of pregnancy. The triple screen tests are for:
  • Alpha-fetoprotein (AFP), a substance naturally produced by the fetus's liver. The level of AFP in the mother's blood increases steadily during pregnancy.
    • An abnormally high AFP level can be a sign of a neural tube defect.
    • An abnormally low AFP level can be a sign of Down syndrome.
  • Human chorionic gonadotropin (hCG), a hormone produced by the placenta when a woman becomes pregnant. The level of hCG steadily increases during the first 8 to 12 weeks of pregnancy, typically peaks around the 10th week, and then gradually decreases. Abnormally high hCG can be a sign of Down syndrome.
  • Estrogen (estriol), which increases during pregnancy. It is produced in large amounts by the placenta. Estriol can be detected in the blood as early as the ninth week of pregnancy and continues to increase until delivery. Abnormally low estriol can be a sign of Down syndrome.

The relatively new quadruple screen combines the triple screen and a test for the hormone inhibin A, which is produced by the fetus and the placenta. One large study of over 23,000 women has reported that the quadruple screen detects almost 86% of all Down syndrome cases. Based on this study, the quadruple test is more likely to pick up Down syndrome and less likely to be false-positive than the triple screen.¹ This screen is not yet available everywhere.

Some women who are low-risk for birth defects decide not to have the maternal serum screen.

Additional tests

Your health professional may recommend:

• A fetal ultrasound in the second trimester before 20 weeks. An early ultrasound is commonly used to accurately date a pregnancy and identify fetal problems.
• An amniocentesis, between the 15th and 20th weeks of pregnancy, if there is concern about a possible birth defect. (An earlier birth defect testing alternative to amniocentesis is chorionic villus sampling, which is available during the first trimester.)
• Electronic fetal heart monitoring (non-stress) any time after 20 weeks of pregnancy, to monitor how your fetus is doing.

Citations

1. Benn PA, et al. (2003). Incorporation of inhibin-A in second-trimester screening for Down syndrome. Obstetrics and Gynecology, 101(3): 451–454.