Maternal serum thyroid antibodies in early pregnancy and fetal Down's syndrome

Review of epidemiological factors (other than maternal age) that determine the prevalence of common autosomal trisomies

The birth prevalence of each common autosomal trisomy (21, 18 and 13) increases with advancing maternal age and this is the most important epidemiological risk factor. Prevalence during pregnancy is also dependent on gestational age. Other factors claimed to influence prevalence include paternal age, ethnicity, family history, premature reproductive aging, parity, twinning, smoking, environmental exposures, maternal medical conditions, and predispositions. We review the evidence for these associations since they may provide insights into causal mechanisms. When investigating potential co-factors it is important to adequately allow for maternal age and minimize its confounding contribution. This is well illustrated by reports of an inverse paternal age effect where there is strong correlation between parental ages. Gestational age at diagnosis, availability of prenatal screening, diagnostic testing, and elective termination of affected pregnancies and healthcare disparities also confound the studies on ethnicity, medical conditions, and predispositions or environmental factors. Data from twin zygosity studies demonstrate the importance of differences in fetal viability for affected pregnancies. We conclude that existing epidemiological evidence for most of the co-factors discussed should currently be considered tenuous; history of Down syndrome, albeit biased, may be an exception. The co-factors may yet provide clues to hitherto poorly understood causal pathways.

Maternal health conditions during pregnancy and acute leukemia in children with Down syndrome: A Children's Oncology Group study

BACKGROUND

Children with Down syndrome (DS) have about a 20-fold increased risk of developing leukemia. Early childhood infections may protect against acute lymphoid leukemia (ALL) in children with and without DS. We examined whether maternal infections and health conditions during pregnancy were associated with acute leukemia in children with DS.

PROCEDURE

We conducted a case-control study of 158 children with DS and leukemia (including 97 cases with acute lymphoblastic leukemia (ALL) and 61 cases with acute myeloid leukemia (AML)) and 173 children with DS during the period 1997-2002. Maternal interview included information about 14 maternal conditions during gestation that are likely to induce an inflammatory response. We evaluated their prevalence in cases and controls. Five of these were common enough to allow analyses by leukemia subtype.

RESULTS

Vaginal bleeding was the most frequent (18% cases, 25% controls) and was associated with a reduced risk (odds ratio (OR) = 0.57; 95% confidence interval (CI) = 0.33-0.99) for all cases combined. Other variables, while showing a potential trend toward reduced risk had effect estimates, which were imprecise and not statistically significant. In contrast, amniocentesis was marginally associated with an increased risk of AML (OR = 2.06, 95% CI = 0.90-4.69).

CONCLUSIONS

Data from this exploratory investigation suggest that some health conditions during pregnancy may be relevant in childhood leukemogenesis. Larger epidemiological studies and other model systems (animal, clinical studies) may provide a clearer picture of the potential association and mechanisms.

Down syndrome screening marker levels in women with a previous aneuploidy pregnancy

BACKGROUND

In Down syndrome screening programmes, women with a previous affected pregnancy are assumed to have the same marker distribution as those without a family history. This assumption needs to be tested.

METHODS

Information on previous aneuploidy pregnancies was routinely sought on the test request forms in three centres, Leeds, Romford and the Fetal Medicine Centre, London. For each woman with a previous aneuploidy (case), five unaffected pregnancies to women without a history were selected as controls. The markers tested included maternal serum free beta-human chorionic gonadotrophin (hCG), pregnancy-associated plasma protein A (PAPP-A), alpha-fetoprotein, unconjugated estriol and ultrasound nuchal translucency thickness.

RESULTS

There were 375 cases: 303 with previous Down syndrome, 63 with Edwards syndrome and 9 with Patau's syndrome. There was a statistically significant difference between cases and controls, in the distribution of free beta-hCG and PAPP-A levels, adjusted for gestation. On average, free beta-hCG was increased by 10% in a subsequent pregnancy after aneuploidy (p < 0.005, Wilcoxon rank sum test) and for PAPP-A the increase was 15% (p < 0.0001). No other marker was significantly different.

CONCLUSION

Risk calculation algorithms need to be modified to take account of the increased marker levels. Until data from sufficient affected pregnancies are available for study, it would be prudent to assume that the same increase as in unaffected pregnancies applies.

Epidemiology of leukemia in children with Down syndrome

Studies suggest nearly a 20-fold increased risk of leukemia in individuals with Down syndrome. Most of this increased risk appears in the first few decades of life, with the highest incidence in children less than 5 years of age. It is unknown why children with Down syndrome are at such an increased risk of leukemia. With respect to environmental exposures, it will be important to investigate risk factors associated with childhood leukemia in general (including diagnostic x-rays, pesticides, and other occupational exposures) as well as experiences common to children with Down syndrome (including routine medical screening tests, increased susceptibility to infections, and increased vitamin deficiencies).

Thyroid antibodies are not a risk factor for pregnancies with Down syndrome

The observation that thyroid disease is frequent in mothers of children with Down syndrome (DS) has suggested that maternal thyroid antibodies could be a factor predisposing to trisomy 21 in their offspring. In this study, the incidences of thyroglobulin (Tg) and thyroid peroxidase (TPO) antibodies were analysed with a sensitive solid-phase immunosorbent radioassay in sera from 29 mothers giving birth to children with trisomy 21 and 87 control mothers. The serum samples were collected at delivery. There was no statistical difference regarding the proportion of thyroid antibodies (against Tg and/or TPO) in the two groups. Thyroid antibodies were detected in 6/29 (20.7 per cent) of the DS mothers and in 23/87 (26.4 per cent) of the control mothers. Among the women with thyroid antibodies, 4/6 (66.7 per cent) of the DS mothers and 12/23 (52 per cent) of the control mothers had antibodies against both Tg and TPO. There was no increase in the relative risk of having a child with DS if the titre of either Tg or TPO antibodies or both were positive, i.e. > or = 1/5. The results indicate that the presence of thyroid antibodies in the serum of a pregnant women has no prognostic value for the birth of an infant with DS.

Frequency of trisomy 21 in Germany before and after the Chernobyl accident

For Berlin (West) the rate of trisomy 21 among newborn and all prenatally diagnosed cases can be almost completely recorded, including the maternal age distribution. During the 9-year-period from 1980 and 1988 the average number of trisomy 21 per month was about 2, following a Poisson distribution. A significant increase (P less than 0.01) was observed in January 1987, exactly 9 months after the Chernobyl accident. In a supraregional study based on greater than 30,000 prenatal diagnoses performed in 1986, no significant effect could be observed. However, the highest rates of trisomy 21 were observed in the more heavily contaminated, southern part of Germany. The majority of these fetuses were conceived during the period of greatest radioactive exposure. The data are discussed with respect to the effect of low-dose radiation around the time of conception on the induction of non-disjunction in man.