A 30-year-old G1P0 at 8 weeks’ gestation presents for her first prenatal visit. She has no significant past medical or surgical history. A 29-year-old friend of hers just had a baby with Down syndrome and she is concerned about her risk of having a baby with the same problem. The patient reports no family history of genetic disorders or birth defects.
You offer her a first trimester ultrasound looking for ultrasound markers associated with Down syndrome.
Which of the following ultrasound markers is most closely associated with Down syndrome?
All of the markers listed are associated in some degree with Down syndrome as well as other genetic abnormalities, but increased NT is most closely and consistently associated. Increased NT is an early presenting feature of Down syndrome. Guidelines for systemic measurement of NT are standardized. Specific training and ongoing audits of examination quality are required for screening programs in order to ensure the expected detection rate. The optimal time to schedule NT measurement is between 12 and 13 weeks, but results are considered valid between 10 4/7 and 13 6/7 weeks. This results in Down syndrome detection rates of 72% at a screen positive rate of 5%. Most centers use a thickness of >/= 3 mm to define abnormal.
In order to increase the detection rate for Down syndrome in the first trimester, you may also offer her which of the following tests in addition to the NT measurement?
Several large, multicenter trials have shown that, in the first trimester, a combination of NT measurement, maternal age, and serum markers (PAPP-A and free or total β-hCG) is a reliable test for Down syndrome, with a detection rate of approximately 84%. Serum AFP is available as a screen for NTDs, and should be ordered after 15 weeks. Inhibin level alone is not a screen for Down syndrome, but may be part of a Quad screen. Amniocentesis cannot be offered until the second trimester. Fetal echocardiogram is not reliable in the first trimester, may not show cardiac defects in the first trimester, and is not considered a screening test for Down syndrome. It may be ordered in fetuses suspected to have Down syndrome based on abnormal diagnostic testing
The patient has an abnormal first trimester screen with increased risk of Down syndrome reported. What is the most appropriate next step?
The patient should be referred for genetic counseling and offered a diagnostic test such as CVS or amniocentesis. Genetic counseling alone is not adequate, and referral to a high-risk specialist is not indicated at this time. The patient should not be told that the baby has Down syndrome, as the first trimester screen has a 5% false positive rate, and requires follow-up diagnostic testing. The patient should not be offered termination at this point, but it would be reasonable to offer termination if diagnostic testing confirmed Down syndrome.
A 20-year-old woman presents to your office for routine well-woman examination. She has a history of acne, for which she takes minocycline and isotretinoin on a daily basis. She has a history of epilepsy that is wellcontrolled on valproic acid. She also takes a combined oral contraceptive birth control pill containing norethindrone acetate and ethinyl estradiol. She is a nonsmoker but drinks alcohol on a daily basis. She is concerned about the effectiveness of her birth control pill, given all the medications that she takes. She is particularly worried about the effects of her medications on a developing fetus in the event of an unintended pregnancy.
Which of the following substances that she ingests has the lowest potential to cause birth defects?
Alcohol is an enormous contributor to otherwise preventable birth defects. Sequelae include retardation of intrauterine growth, craniofacial abnormalities, and mental retardation. The occasional drink in pregnancy has not been proved to be deleterious, but is still not recommended. Isotretinoin (accutane) is a powerful drug for acne that has enormous potential for producing congenital anomalies when ingested in early pregnancy; it should never be used in pregnancy. Tetracyclines interfere with development of bone and can lead to stained teeth in children. Progesterones have been implicated in multiple birth defects, but controlled studies have failed to demonstrate a significant association with increased risk. Patients who have inadvertently become pregnant while on birth control pills should be reassured that the incidence of birth defects is no higher for them than for the general population. Valproic acid is used for epilepsy and can be associated with a spectrum of abnormalities, including NTDs and abnormal facial features.
A 24-year-old woman is in a car accident and is taken to an emergency room, where she receives x-ray examinations of her neck, chest, and lower spine. It is later discovered that she is 10 weeks pregnant.
Which of the following is the most appropriate statement to make to the patient?
While a 50-rad exposure in the first trimester of pregnancy would be expected to entail a high likelihood of serious fetal damage and wastage, the anticipated fetal exposure for chest x-ray and one film of the lower spine would be less than 1 rad. This is well below the threshold for increased fetal risk, which is generally thought to be 10 rads. High doses of radiation in the first trimester primarily affect developing organ systems such as the heart and limbs; in later pregnancy, the brain is more sensitive. The chromosomes are determined at the moment of conception. Radiation does not alter the karyotype, and determination of the karyotype is not normally indicated for a 24-year-old patient. The incidence of leukemia is raised in children receiving radiation therapy or those exposed to the atomic bomb, but not from such a minimal exposure as here.
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