Maternal serum screening for fetal down syndrome using alpha-fetoprotein, human chorionic gonadotrophin, and unconjugated estriol in adolescents

Adolesc Pediatr Gynecol (1993) 6:91-94

Adolescent and Pediatric Gynecology © 1993 Springer-Verlag New York Inc.

Maternal Serum Screening for Fetal Down Syndrome Using Alpha-Fetoprotein, Human Chorionic Gonadotrophin, and Unconjugated Estriol in Adolescents Owen P. Phillips, M.D., Lee P. Shulman, M.D., Sherman Elias, M.D., and Joe Leigh Simpson, M.D. Division of Reproductive Genetics, Department of Obstetrics and Gynecology. University of Tennessee, Memphis. Tennessee

Abstract. Study Objective: To learn whether accuracy and false-positive rate of our maternal serum screening program for fetal Down syndrome differed in adolescents compared with adults. In addition. we studied the degree to which overestimated gestational age accounted for screen-positive results and the rate at which amniocentesis was elected by patients in different age groups. Design: Maternal serum screening using human chorionic gonadotropin (heG), alpha-fetoprotein, unconjugated estriol and age was offered for fetal Down syndrome to all women between 15 and 20 weeks gestation who were less than or equal to 35 years of age at date of delivery. Women found to have a risk for fetal Down syndrome of ;;" 1:274 were considered screen-positive. If gestational age was confirmed by ultrasound, then genetic counseling and amniocentesis were offered. Results: Of 10,627 women screened, 2,237 (21.1% of population screened) were between ages 12 and 19 years. Of these adolescents, 175 (7.5%) were screen positive. Of these 175, 114 (65.1%) were found by ultrasonographic examination to have overestimated gestational age, and compared with adult women (ages 20-34 years); this was statistically significant (p < 0.003). Of the remaining 61 patients, 13(21.3%) were lost to follow-up. The remaining 48 were offered genetic counseling and amniocentesis, of whom 38 (79.2%) elected to have amniocentesis. In the total population screened, four of seven Down syndrome cases were detected, one in a 19-year-old. In the three cases not detected, one was in a 19-year-old and one was in a 22-year-old. Conclusions: Fetal Down syndrome screening may not be as sensitive in younger women as in older women, however, counseling and management in adolescents need not

Address reprints requests to: Owen P. Phillips, M.D.. Department ofOb/Gyn, Elm, 853 Jefferson, Memphis TN 38103, USA.

Presented at the North American Society of Pediatric and Adolescent Gynecologic Society annual meeting April 4-6, 1992. Nashville, TN; recipient of the Huffman-Capraro Award.

differ from that of adults. Appropriate diagnostic procedures should be offered to all women at increased risk for fetal Down syndrome.

Key Words. Maternal serum screening-Adolescent pregnancy-Down syndrome

Introduction Maternal serum screening for fetal neural tube defects has become an accepted part of obstetrical care.' Elevated maternal serum levels of alphafetoprotein (MSAFP) are associated with anencephaly and open spina bifida.? In addition, elevated MSAFP may indicate multiple gestation.' fetal demise, fetal ventral abdominal wall defects (omphalocele or gastroschisis)," or underestimated gestational age. In 1984, Merkatz et al." found second-trimester MSAFP to be lower in pregnancies associated with fetal Down syndrome compared with unaffected pregnancies. Others confirmed this association," and screening for fetal Down syndrome using MSAFP in combination with maternal age is now commonly offered. However, only 2025% of fetal Down syndrome cases can be detected among women who are "'S35 years of age at estimated delivery date. In 1986, Bogart et al." found second-trimester maternal serum levels of human chorionic gonadotropin (l3-hCG) to be elevated in pregnancies associated with fetal Down syndrome compared with unaffected pregnancies. Canick et al. 8 found second-trimester maternal serum levels of unconjugated estriol (uE3) to be lower compared with un-

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affected pregnancies. Maternal serum screening for fetal Down syndrome using AFP, hCG, and uE3 in conjunction with maternal age has been predicted to have a detection rate of 67% if women of all age groups were tested." We have previously published results of our maternal serum screening program using MSAFP, hCG, and uE3 for fetal Down syndrome in women less than 35 years of age and found an overall detection rate of 57% and a false-positive rate of 3.2%.10 In the current study, we chose to focus attention on fetal Down syndrome screening in adolescents. We sought to compare the rate at which adolescents were found to be at increased risk for fetal Down syndrome by maternal serum screening (screen-positive) as compared with older age groups and the degree to which incorrect gestational dating accounted for screen-positive results in different age groups. Outcome of patients found to be screen positive according to maternal age was also addressed. Risk for fetal Down syndrome is related to a woman's age. II Likelihood ratios (LR) are derived based on maternal serum levels of AFP, l3-hCG, and uE3; the LR is then multiplied by the agerelated risk to calculate a patient-specific fetal Down syndrome risk." Women with a calculated risk equal to or greater than a specified cutoff (e.g., risk of a 35-year-old at midtrimester or ? I :274) are offered genetic counseling and amniocentesis. In adolescents, the a priori risk is relatively low; therefore, theoretically fewer young women should be called screen positive compared with older women. 11 It follows then that fetal Down syndrome screening may be less efficient in adolescents compared with adults. Methods Fetal Down syndrome screening was performed in conjunction with fetal neural tube defect screening; these tests are offered to all women at low risk for these particular birth defects. Women at increased risk for chromosomal abnormalities (e.g., women age ?35 years at estimated date of delivery, 12 previous offspring with a chromosomal abnormality, parental chromosomal translocation) were directly counseled about invasive prenatal diagnostic procedures, specifically amniocentesis and chorionic villus sampling. Screening was offered between 15 and 20 weeks' gestation inclusive. The screening protocol as well as specifics concerning the analyte assays are detailed in a previously published work. 10 For each maternal sample, a likelihood ratio is calculated from AFP, l3-hCG, and uE3 MOM values l 1

using the Alpha Program (Logical Medical Systems, London, UK).9 A patient-specific risk is then derived by multiplying the trivariate likelihood ratio by the woman's age-risk for fetal Down syndrome. A screen was considered "positive" for fetal Down syndrome if the adjusted risk was ?1:274, i.e., the risk of a 35-year-old having a fetus with Down syndrome in the second trimester. Positive screens were not repeated. 13 If a woman was found to be screen positive and had not undergone ultrasonographic gestational dating, such an examination was offered to exclude overestimation of gestational age. The assigned gestational age was "explained" only if ultrasonographic dating differed from original dating by 10 days or more. If so, values were then reinterpreted based on new ultrasonographic dating. Women found to be less than 15 weeks pregnant at the time of sampling were informed that risk estimation was not possible, and a second sample was requested between 15 and 20 weeks. All women with screen positive results unexplained by ultrasonography were offered genetic counseling and amniocentesis. Contact with patients and arrangement for follow-up was made by a nurse coordinator; telephone contact as well as notification by regular and certified mail was performed. Patients were considered "lost to followup" if they could not be reached for notification or if they failed to show for genetic clinic appointments. Pregnancy outcome data were obtained by reviewing all newborn chromosome studies performed by the University of Tennessee cytogenetics laboratory (which services most hospitals in our referral area) and by cross-referencing these cases to our maternal screening database. For the purposes of this study, adolescence was defined as being 12-19 years of age; those patients between 20 and 34 years of age were considered adults. Statistical analysis was done by chi-square analysis.

Results From January 1990 through February 1992, 10,627 women under 35 years of age were screened for fetal Down syndrome. Of these, 2,337 (21.1%) were between ages 12 and 19. Screening results according to age groups are presented in Table 1. Although the percentage of women found to be screen positive for fetal Down syndrome tends to increase with maternal age, no statistically significant difference was found in the adolescent population (12-15 and 16-19 years of age) compared with adult women (20--34 years of age). However, the percentage ex-

Phillips et al.: Maternal Serum Screening for Fetal Down Syndrome

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Table 1. Outcome of Fetal Down Syndrome Screening According to Maternal Age

Age

Total Screened

12-15 1fr-19 Total adolescents 20-29 30-34 Total adults

233 2,104 2,337 5,910 1,282 7.192

Total Positive (%) 15 (6.4) 1600.6)

Explained by Ultrasound (%) 7 (46.7) 107 (66.9)

1750.5%)"

114 (65.I'kl

4250.3)

105 (8.2)

234 (55. \) 44 (41.9)

5300.4%)"

278 (52.5%)b

Unexplained by Ultrasound (%) 8 (53.3) 53 (33.1) 61 (34.9%) 191 (44.9) 61 (58. \) 252 (47.6%)

up < 0.9: "p < 0.003.

plained by ultrasonographic examination in adolescents was higher (65.1 %) compared with adults (52.5%; p < 0.003) (incorrect gestational dating). Among patients whose screen positive results were unexplained by ultrasonography, adolescent patients were more likely than adults to be lost to follow-up (21.3% vs. 14.3%); however, the difference was not statistically significant (p = 0.2). Of those patients receiving genetic counseling, no statistically significant difference was found between adolescents and adults in regard to the percentage electing amniocentesis (Table 2). Four cases of fetal Down syndrome were detected by our maternal serum screening program. One case was in a 19-year-old whose risk was raised from I: 1200 to I: 110; (analyte values were MSAFP 0.75, uE3 0.76, hCG 3.24). The other three cases were in women ages 25, 28, and 29 years. In three additional cases of fetal Down syndrome, triple analyte screening failed to identify the pregnancies to be at increased risk. One case was in a 19-year-old (analyte values MSAFP 1.04, uE3 1.16, hCG 5.47), in which the risk was raised substantially (from I: 1200 to I :300), but not sufficiently increased to be considered screen positive (1 :274). Fetal Down syndrome was similarly not detected in two other women ages 22 and 30 years, respectively. In the 22-year-old, analyte values were MSAFP 0.89, uE3 0.77, hCG 1.18; the risk was raised from 1:1100 to 1:930. Table 2. Amniocentesis Rates Among Women Receiving Genetic Counseling According to Maternal Age

Age 12-15 1fr-20 Total adolescents 21-29 30-34 Total adults "p < 0.9.

Seen in Genetics Clinic 7 41

Declined Amniocentesis (%) 2 (28.6) 8 (\9.5)

Elected Amniocentesis (%)

5 01.4)

33 (80.5)

48 162 54

10 (20.8%)U 31 (19. \) II (20.4)

38 (79.2%) 131 (80.9) 43 <79.6)

216

42 (19.4%)U

174 (80.6%)

Discussion Although older women are more likely to have offspring with Down syndrome, most children with Down syndrome are born to younger wornen.l" Therefore, screening should be offered to all women less than 35 years of age. Because of the low a priori risk for fetal Down syndrome in adolescents, which is used in calculation of patient-specific risk, it is predicted that screening for fetal Down syndrome among adolescents would find a smaller percentage to be screen positive than among adults. Knight et al. II found this to be the case when screening with MSAFP and age alone; only women aged 20-34 years were studied. The percentage of women found to be screen positive fell steadily with decreasing maternal age. In our fetal Down syndrome screening program using MSAFP, hCG, uE3, and maternal age, no difference was found in initial screen-positive results between adolescents (age 12-19) and older women (ages 20-34). However, a greater percentage of positive screens in adolescents compared with adults (p < 0.03) was explained by ultrasonographic examination. As might be predicted, adolescents were more likely to have poor menstrual dating with subsequent overestimation of gestational age, causing screen positive results. Therefore, our data find adolescents less likely to be identified as candidates for amniocentesis than adults, consistent with that of Knight et al. l l However, more than one-third of adolescents remained at high risk for fetal Down syndrome after ultrasonographic examination. Compared with adults, adolescents were less likely to respond to contact attempts or to keep genetic clinic appointments, although the difference was not statistically significant. Possible explanations of these observations in adolescents include lack of understanding about Down syndrome or the implication of a positive screen. Although all women are counseled about fetal Down syndrome screening prior to testing and are given the opportunity to accept or decline testing, more indepth education about the test may be necessary in younger pregnant women. However, of those who

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did attend genetics clinic and received counseling, no statistically significant difference was found in the percentage electing to undergo amniocentesis among different age groups. Our screening program using maternal serum levels of AFP, uE3, and l3-hCG in conjunction with maternal age detected four of seven (57%) fetal Down syndrome cases.!" a finding consistent with theoretical predictions." We detected one case in a 19-year-old; however, the screen did not detect cases in a 19-year-old and a 22-year-old. Knight et al. 11 found that the detection rate of fetal Down syndrome screening with MSAFP and age alone fell with decreasing maternal age, from 46% detection in 34-year-olds to 8.2% in 20-year-olds. The number of women screened in our study is too small to assess accuracy in different age groups. Larger numbers may find that fetal Down syndrome screening with MSAFP, hCG, and uE3 may be less efficient in younger patients. At present, however, we believe counseling and management of the screening in adolescents should not differ from that of the adult population and that appropriate diagnostic procedures should be offered to all women identified to be at increased risk for fetal Down syndrome.

References 1. Antenatal Diagnosis of Genetic Disorders. Genetic

ACOG Technical Bulletin #108, September. 1987 2. Johnson AM, Palomaki GE, Haddow JE: Maternal serum alpha-fetoprotein levels in pregnancies among black and white women with open spina bifida: a United States collaborative study. Am J Obstet Gynecol 1990; 162:328 3. Thorn H, Buckland CM, Campbell AGM: Maternal serum AFP in monozygotic and dizygotic twin pregnancies. Prenat Diagn 1984; 4:341 4. Palomaki GE: Second trimester maternal serum alpha-feto protein levels in pregnancies associated with

gastroschisis and omphalocele. Obstet Gynecol 1988; 71:906 5. Merkatz IR, Nitowsky HM, Macri IN, Johnson WE: An association between low maternal serum alpha fetoprotein and fetal chromosomal abnormalities. Am J Obstet Gynecol 1984; 148:886 6. New England Regional Genetics Group Prenatal Collaborative Study of Down Syndrome Screening: Combining maternal serum alpha-fetoprotein measurements and age to screen for fetal Down syndrome in pregnant women under age 35. Am J Obstet Gynecol 1989; 160:175 7. Bogart MH. Pandian MR, Jones OW: Abnormal maternal serum chorionic gonadotropin levels in pregnancies with fetal chromosome abnormalities. Prenat Diag 1987; 7:623 8. Canick JA, Knight GJ, Palomacki GE, et al.: Low second trimester maternal serum unconjugated oestriol in pregnancies with Down syndrome. Br J Obstet Gynecol 1988; 95:330 9. Wald NJ, Cuckle HS, Densem JW, et al: Maternal serum screening for Down's syndrome in early pregnancy. Br Med J 1988; 297:883 10. Phillips OP, Elias S, Shulman LP, et al.: Maternal serum screening for fetal Down syndrome with MSAFP, human chorionic gonadotropin and unconjugated estriol in women less than 35 years of age: a prospective 2-year study. Obstet Gynecol 1992; 80: 353 11. Knight GJ, Palomaki GE, Haddow JE: Use of maternal serum alpha-fetoprotein measurements to screen for fetal Down syndrome. Clin Obstet Gynecol 1988; 31:306 12. Hook EG, Cross PK, Schreinemachers DM: Chromosome abnormality rates at amniocentesis and in live-born infants. N Engl J Med 1983; 249:2034 13. Cuckle HS, Wald NJ, Nanchahual K, Densem JW: Repeat maternal serum alpha-fetoprotein testing in antenatal screening programmes for Down's syndrome. Br J Obstet Gynecol 1989; 96:52 14. Youings S, Gregson N, Jacobs P: The efficacy of maternal age screening for Down's syndrome in Wessex. Prenat Diag 1991; 11:419