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An arbitrary age of 35 years has previously functioned in the United States as an expected standard of care, which requires that a prospective mother be informed of her increased risks of having a child with a chromosome defect, informed of the recommendation for prenatal diagnosis, and given an explanation of the risks of CVS or amniocentesis, with the associated details related to any problems, pitfalls or reservations. Now, given the very low procedural risks, all women should be offered routine prenatal genetic studies that focus on chromosomal analysis and α‐fetoprotein (see Chapter 17). Advances in fetal imaging and low risks of fetal loss following amniocentesis (0.1–0.4 percent) or CVS (0.2–0.4 percent)^{404, 405} (see Chapter 9) have led to the policy change. The advent of noninvasive prenatal testing (see Chapters 6 and 7) has further decreased the need for CVS or amniocentesis.

Excluding infants with chromosome abnormalities, a prospective analysis of 102,728 pregnancies (including abortions, stillbirths, and livebirths) in Texas found that the incidence of congenital malformations increased significantly and progressively in women after 25 years of age.⁴⁰⁶ The authors found that an additional age‐related risk of nonchromosome malformations was approximately 1 percent in women 35 years of age or older. The odds ratio for cardiac defects was 3.95 in infants of women 40 years of age or older when compared with women aged 20–24 years.

Pregnancy outcomes related to maternal age were reported in a Danish study of 369,516 singleton cases.⁴⁰⁷ Pregnancies were followed from 11–14 weeks to delivery or termination and the age groups (20–34, 35–39, and ≥40 years) compared. Adverse outcomes included chromosomal abnormalities, congenital malformations, miscarriage, stillbirth, and delivery prior to 34 weeks of gestation. Women ≥40 years had a 3.83 percent risk of chromosomal abnormality, compared with 0.56 percent in the younger age group. Other significant results were an odds ratio of 3.1 for miscarriage (1.68 percent vs. 0.42 percent) and an odds ratio of 1.66 (2.01 percent vs. 1.21 percent) for birth <34 weeks of gestation.