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Objectives: The proportion of Down's syndrome pregnancies detected prenatally in England and Wales is lower in younger mothers than in older mothers. This paper examines the reasons for this apparent age inequality., Methods: We used data from the National Down Syndrome Cytogenetic Register (NDSCR) to examine the time trend of the proportion of Down's syndrome pregnancies diagnosed prenatally according to maternal age over the years 1989-2004 in England and Wales., Results: A lower proportion of younger mothers had their Down's syndrome pregnancy detected prenatally than older mothers; however, this gap has been closing over time. For example, for mothers under 25 years of age only 13% of Down's syndrome pregnancies were detected prenatally from 1989 to 1992, with this figure rising to 34% in 2001-2004, compared with proportions of 74% in both periods for mothers over 44 years of age. A lower uptake of screening among younger women could not explain these differences. The differences in detection rates of the screening methods according to maternal age, particularly of the older screening tests, could account for these differences., Conclusions: The closing gap between the proportions of younger and older women having their affected pregnancy prenatally diagnosed is a confirmation of the improvement of screening methods over time.

Objectives: To determine the recurrence risk of a free trisomy 21 pregnancy., Methods: Data from the National Down Syndrome Cytogenetic Register (NDSCR), which contains information on nearly all cases of Down syndrome between 1989 and 2001 in England and Wales were used. Among 11 281 women with a Down syndrome pregnancy who had had at least one previous pregnancy there were 95 women who had had a previous Down syndrome pregnancy., Results: Women who have had a previous Down syndrome pregnancy have a constant absolute excess risk above their maternal age-related risk of having a subsequent affected pregnancy. This absolute excess risk is determined by the age at which the affected pregnancy occurred and is higher for younger than for older women. For example, after a Down syndrome pregnancy at age 20, this excess is 0.62% (95% CI: 0.24 to 1.15%) at early second trimester, and, after one at age 40, it is 0.04% (95% CI: 0.01 to 0.07%)., Conclusion: More precise risk estimates by single year of maternal age for use in genetic counselling are provided, but they need validation from other studies before they are incorporated in the risk estimation routines used in Down syndrome screening programmes., (Copyright 2005 John Wiley & Sons, Ltd)

Objective: Whether the introduction of antenatal screening for Down syndrome in England and Wales with serum biochemistry or ultrasound has led to improvements in patient outcomes is unknown. The purpose of this study was to relate pregnancy outcomes to the dominant method used for prenatal Down syndrome screening., Study Design: For the years 1989 through 1999, England and Wales were divided into geographically defined areas where specific hospitals, health authorities, and cytogenetic laboratories provided maternity care for well-defined populations. For each year from 1989 through 1999, the dominant Down syndrome screening method that was used in each area was determined. Outcomes for area-years that used serum biochemistry or ultrasound (first or second trimester) were compared with area-years that used advanced maternal age as the dominant screening method. The percent of Down syndrome cases that were diagnosed prenatally (effectiveness) and the number of invasive prenatal tests that were performed to diagnose each Down syndrome case prenatally (efficiency) were compared., Results: There were 5,980,519 births and 335,184 referrals for prenatal karyotyping (amniocentesis and chorionic villus sampling) that occurred in the area-years studied, of which 12,047 pregnancies were diagnosed as Down syndrome; 5393 cases of Down syndrome (45%) were diagnosed prenatally. Invasive testing increased from 4.4% of pregnancies in 1989 to 6.4% in 1997 and declined slightly in 1999 (5.8%). Prenatal diagnosis of Down syndrome cases rose from 28% in 1989 to 53% in 1999, and the number of invasive tests that were performed to diagnose each Down syndrome case fell from 89.7 to 47.7 (P [for trend]<.0001). Areas with serum or ultrasound as the dominant screening method detected 50% more Down syndrome cases in prenatally (52% and 53% vs 36%; P<.0001) and performed fewer invasive procedures to diagnose each Down syndrome case (60.7 and 52.0 vs 88.0; P<.0001) compared with areas in which advanced maternal age screening was dominant, despite serving populations with similar mean/median maternal ages., Conclusion: In clinical practice, screening programs for Down syndrome that were based on maternal serum biochemistry or ultrasound were more effective and efficient than the screening programs that used advanced maternal age alone.

The national register of chromosomal anomalies that lead to Down's syndrome has enabled the monitoring of change in prenatal diagnosis for this condition, and the factors which affect the change. The proportion of cases of cytogenetically diagnosed Down's syndrome in England and Wales detected prenatally rose to 46% in 1991-2 from 31% in 1988-9, a 1.5-fold increase (95% confidence interval 1.3 to 1.7). The increase was confined to mothers under 40 years and was due to the introduction of screening by maternal serum analysis and ultrasound. Over a quarter of affected pregnancies in women aged 25-29 were detected prenatally in 1991-2 compared with less than 10% in 1988-9. Analysis of the data showed regional differences in prenatal diagnosis rates, and in the length of time elapsing between the diagnostic test and termination of an affected pregnancy. An inexplicable finding was that this period varied with the sex of the fetus, being on average a day longer for females than for males.