Patterns of referral and invasive prenatal diagnosis in women of advanced maternal age, Manitoba, 1990-1995

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Stranc, Leonie
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Pregnant women 35 years or older at delivery represent the largest users of prenatal genetic services in Canada: in 1990, 78% of referrals for prenatal testing were because of advanced maternal age (AMA), yet this represented only 52% of eligible women. The degree to which aspects of the organisation and delivery of care and maternal characteristics were involved in the process of obtaining genetic prenatal diagnosis in Manitoba was assessed using a linked dataset. The study sample included all AMA Manitoba women in whom pregnancy had been diagnosed between November 25, 1989 and March 31, 1995 (n = 12,116 determined (n = 1,693) or a miscarriage (n = 1,981) were excluded from the analyses. AMA women who were referred for genetic prenatal diagnosis (n = 3,422) were compared to those who were not referred (n = 5,020). Highly significant predictors of referral included (1) seeing an obstetrician before 16 weeks gestation (odds ratio 4.7, 95% CI 4.1-5.5), (2) a Down syndrome risk determined by serum screening tobe increased over the age-related risk (odds ratio: 2.7, 95% CI: 2.4-3.1), (3) maternal age of 36+ years at term (36-39 years: odds ratio 2.3, 95% CI 2.1-2.5; 40+ years OR 2.2, 95% CI 1.8-2.6), (4) urban residence (odds ratio: 1.9, 95% CI: 1.7-2.2), (5) previous poor obstetric history (odds ratio: 1.9, 95% CI: 1.5-2.5), (6) being in the top income quintile (odds ratio: 1.6, 95% CI: 1.3-1.8) and (7) seeing a general practitioner by 16 weeks (odds ratio: 1.4, 95% CI: 1.2-1.6). Over the study period, approximately 41% (3,422/8,442) of the eligible AMA population was referred for prenatal diagnosis counselling and 74% (2,527/3,422) went on to have invasive genetic prenatal testing. The strongest predictor of uptake of invasive testing was seeing an obstetrician before 16 weeks gestation (odds ratio 2.3, 95% CI: 2.0-2.7). Belonging to either of the top two income quintiles was a stronger predictor of invasive testing than was having a Down syndrome risk increased over the age-related risk (odds ratio Quintile 4: 1.7, 95% CI: 1.3-2.1; odds ratio Quintile 5: 2.0, 95% CI: 1.6-2.5 vs. odds ratio 1.4, 95% CI: 1.2-1.7). A woman was also more likely to have invasive testing if she was between 36-39 years of age, rather than 40+ years at term (odds ratio 1.5, 95% CI: 1.2-1.7, p = 0.0001 vs. odds ratio 1.4, 95% CI: 1.1-1.8, p = 0.0194). Seeing a general practitioner before 16 weeks of pregnancy, urban residence and poor obstetric history were not found to be significant predictors of invasive testing. Early complications of pregnancy had a significant negative association with uptake of invasive testing (odds ratio: 0.6, 95% CI: 0.5-0.8, p = 0.0001).