A pregnant woman has come to you for advice. She is in the second trimester of her pregnancy and by mistake she took thalidomide prescribed for her husband. She is certain that she took the drug early in the pregnancy but is not positive of the exact date. She has come to you to determine whether her child will be born with malformed limbs. What tests you would suggest that could answer her question? Why, and what would the results tell you?
Supposing the father is actively taking thalidomide (as prescribed), and was doing so at the time of conception and for any other unprotected intercourse thereafter, the mother/child may have been exposed to thalidomide for the whole course of the pregnancy, not just the one time the mother accidentally took it. According to a CDC report from 2003, thalidomide can travel through the sperm/semen. In this case, the mother should have a simple blood test (toxicity screen) to determine the levels of thalidomide in her blood. It's important to note that a test of the mother's blood is sufficient because thalidomide is one of a few known drugs that cross the placenta barrier. By the second trimester, though only a couple of inches long, the fetus is nearly fully formed. It has a heartbeat, is starting to produce urine, and can even hiccup and suck its thumb. So if the mother really wanted to know whether her or her husband's use of thalidomide has or is going to lead to phocomelia, a sonogram performed and interpreted by her OB/GYN would be the most definitive test at this stage. There's nothing to be done other than a blood/toxicity test and/or sonogram, though, if the mother's only concern is with malformation of the limbs. Do note that thalidomide can produce other malformations as well.
The circumstances that this woman presents with are indeed cause for concern. A single use of thalidomide early in pregnancy, especially between week 5-7 after her missed menstrual period, can result in fetal malformations.
Although most pregnant women receive an ultrasound scan to look for physical abnormalities around 20 weeks, those who have taken thalidomide may begin receiving more detailed anomaly scans around 12 weeks. The early scans may not pick up physical malformations as accurately as the 20 week and later ultrasounds do. At 20 weeks the doctor may be able to see markers of thalidomide use such as shortened limbs or a cleft palate.
Because ultrasound may not pick up some abnormalities a fetoscopy may be indicated. Although this test is more high risk to both the mother and fetus, it is recommended in cases where the baby has a higher-than-normal chance of developing abnormally. An instrument called a fetoscope allows the physician to see the fetus.
There are two types of tests to determine birth defects in unborn babies. These two types include blood tests and ultrasounds. Ultrasounds are conducted to identify changes in the fetus. Blood tests are used to look for substances in the blood that would indicate a birth defect. Most likely in this situation, the ultrasound would be utilized to see if the fetus was affected by the drug taken in the first trimester.