Serum müllerian-inhibiting substance in Down's syndrome pregnancies

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 serum anti-Müllerian hormone at 11-13 weeks' gestation in the prediction of preeclampsia

OBJECTIVE

To investigate the potential value of maternal serum anti-Müllerian hormone (AMH) at 11-13 weeks' gestation in the prediction of preeclampsia (PE).

METHODS

The serum concentration of AMH was measured at 11-13 weeks' gestation in cases of PE (n = 50) and normotensive controls (n = 150). Backward stepwise multiple regression analysis was used to determine which of the factors amongst the maternal characteristics and gestation were significant predictors of the serum AMH in the control group and from the regression model the value in each case and control was expressed as a multiple of the expected median (MoM).

RESULTS

In normotensive pregnancies, the maternal serum concentration of AMH is higher in Afro-Caribbean than in Caucasian women and in smokers than in non-smokers. In the PE group, the median serum concentration of AMH was significantly higher than in the controls (2.140 ng/L, IQR 1.968-2.273 versus 2.062 ng/L, IQR 1.938-2.181; p = 0.025), but the median MoM value of AMH was not significantly different between the PE group and the controls (1.040, IQR 0.941-1.081 versus 0.995, IQR 0.939-1.065, p = 0.147).

CONCLUSIONS

Maternal serum AMH is not an effective early predictor for PE.

Trisomic pregnancy and elevated FSH: implications for the oocyte pool hypothesis

BACKGROUND

Some studies, but not all, support the hypothesis that trisomy frequency is related to the size of the oocyte pool, with the risk increased for women with fewer oocytes (older ovarian age). We tested this hypothesis by comparing hormonal indicators of ovarian age among women who had trisomic pregnancy losses with indicators among women with non-trisomic losses or chromosomally normal births. The three primary indicators of advanced ovarian age were low level of anti-Müllerian hormone (AMH), high level of follicle-stimulating hormone (FSH) and low level of inhibin B.

METHODS

The analysis drew on data from two hospital-based case-control studies. Data were analyzed separately and the evidence from the two sites was combined. We compared 159 women with trisomic pregnancy losses to three comparison groups: 60 women with other chromosomally abnormal losses, 79 women with chromosomally normal losses and 344 women with live births (LBs) age-matched to women with losses. We analyzed the hormone measures as continuous and as categorical variables. All analyses adjust for age in single years, day of blood draw, interval in storage and site.

RESULTS

AMH and inhibin B did not differ between women with trisomic losses and any of the three comparison groups. Mean ln(FSH) was 0.137 units (95% confidence interval (CI): 0.055, 0.219) higher for trisomy cases compared with LB controls; it was also higher, though not significantly so, for trisomy cases compared with women with other chromosomally abnormal losses or chromosomally normal losses. The adjusted odds ratio in relation to high FSH (≥ 10 mIU/ml) was significantly increased for trisomy cases versus LB controls (adjusted odds ratio (OR): 3.8, 95% CI: 1.6, 8.9).

CONCLUSIONS

The association of trisomy with elevated FSH is compatible with the oocyte pool hypothesis, whereas the absence of an association with AMH is not. Alternative interpretations are considered, including the possibility that elevated FSH may disrupt meiotic processes or allow recruitment of abnormal follicles.

Maternal antimullerian hormone levels do not predict fetal aneuploidy

PURPOSE

To determine if diminished ovarian reserve (measured by maternal antimullerian hormone (AMH) levels), is associated with fetal aneuploidy (determined by prenatal karyotype).

METHODS

This case-control study included 213 women with singleton pregnancies who underwent both serum aneuploidy screening and invasive prenatal diagnosis. 18 patients carrying an aneuploid fetus served as cases and the remaining 195 women with a euploid fetus were controls. Serum AMH was measured using two assays: AMHbc (Beckman-Coulter) and AMHdsl (Diagnostic Systems Laboratories). Karyotypes were determined by chorionic villus sampling or amniocentesis.

RESULTS

AMHbc levels did not differ between women with an aneuploid fetus and women with a euploid fetus (p = 0.46) and did not predict aneuploidy (ROC Area = 0.57). Additionally, AMHbc values declined significantly with advancing gestational age.

CONCLUSIONS

Maternal AMH does not appear to be a marker of fetal aneuploidy in ongoing pregnancies. Contrary to previous reports, we found a significant decline in maternal AMH levels with advancing gestational age.

On the origin of the maternal age effect in trisomy 21 Down syndrome: the Oocyte Mosaicism Selection model

We have recently documented that trisomy 21 mosaicism is common in human foetal ovaries. On the basis of this observation we propose that the maternal age effect in Down syndrome (DS) is caused by the differential behaviour of trisomy 21 in relation to disomy 21 oocytes during development from foetal life until ovulation in adulthood. In particular, we suggest that trisomy 21 oocytes, lagging behind those that are disomic, may escape the timed pruning of the seven million in foetal life to the 300–400 finally selected for ovulation. The net effect of this preferential elimination will be an accumulation of trisomy 21 oocytes in the ovarian reserve of older women. We here highlight the implications of this Oocyte Mosaicism Selection (OMS) model with respect to the prevalent view that the maternal age effect is complex, dependent on many different biological and environmental factors. We examine conclusions drawn from recent large-scale studies in families, tracing DNA markers along the length of chromosome 21q between parents and DS children, in comparison to the OMS model. We conclude that these family linkage data are equally compatible with the maternal age effect originating from the accumulation of trisomy 21 oocytes with advancing maternal age. One relatively straightforward way to get to grips with what is actually going on in this regard would be to compare incidence of trisomy 21 oocytes (and their pairing configurations) in foetal ovaries with that in oocytes at the meiosis I stage from adult women.

Epidemiology of Down syndrome

Down syndrome (DS) is the most commonly identified genetic form of mental retardation and the leading cause of specific birth defects and medical conditions. Traditional epidemiological studies to determine the prevalence, cause, and clinical significance of the syndrome have been conducted over the last 100 years. DS has been estimated to occur in approximately 1 in 732 infants in the United States, although there is some evidence that variability in prevalence of estimates exist among racial/ethnic groups. Progress has been made in characterizing the specific types of chromosome errors that lead to DS and in identifying associated factors that increase the risk of chromosome 21 malsegregation, i.e., advanced maternal age and recombination. Studies to examine the variability of the presence of specific DS-associated birth defects and medical conditions provide evidence for genetic and environmental modifiers. Here, we provide a brief survey of studies that address the current state of the field and suggest gaps in research that can soon be filled with new multidisciplinary approaches and technological advances.