Review Question - QID 103385

A number of tests are performed at the first prenatal visit to evaluate potential risks in pregnancy such as Rh factor incompatibility, HIV, or lack of immunity to Rubella. After these tests are performed, most are not repeated in the third trimester. In pregnant patients found to have a sexually transmitted infection, repeated screening for these conditions is recommended during the third trimester. During the third trimester, typically at around 35 weeks gestation, rectovaginal swab and culture to detect Group B Streptococcus (GBS) is recommended. GBS is commonly found in the rectovaginal flora of otherwise healthy pregnant women. Furthermore, it is the most common cause of neonatal pneumonia, meningitis, and sepsis. Women identified to be carriers of GBS receive intrapartum penicillin to prevent transmission to the infant during delivery. This reduces the risk of GBS infection in infants. For pregnant women who are found to be carriers of GBS on urinalysis at any point in the pregnancy, or who have had children with GBS infection previously, rectovaginal swab is not performed and intrapartum penicillin is administered empirically.

Kitchen et. al review guidelines for prenatal screening throughout pregnancy. They discuss first trimester screening tests and conditions in which patients require further follow up or repeat screening. They note the risk of GBS infection in newborns, and discuss the recommendation for GBS screening in all pregnant women.

Illustration A displays a typical prenatal care timeline.

Incorrect Answers:
Answer 1: Blood type and screen is performed at the initial prenatal visit to determine Rh status, and does not need to be repeated in the third trimester

Answer 2: Hepatitis B serology is performed at the initial prenatal visit. For most patients without subsequent exposure or risk factors for hepatitis B infection, serology is not repeated in the third trimester.

Answer 3: HIV screening should be performed in the first trimester. Additionally screening in the third trimester is recommended by ACOG for women in areas with high HIV incidence or prevalence and women known to be at risk of acquiring HIV infection.

Answer 5 Rubella serology is performed at the initial prenatal visit and does not need to be repeated in the third trimester

Bullet Summary
Pregnant women are recommended to have rectovaginal swab performed late in the third trimester to determine Group B Streptococcus carrier status.