Objective: To investigate the association between advanced maternal age and stillbirth risks in first, second, third, and fourth births or more.
Methods: A population-based registry study including all women aged 25 years and older with singleton pregnancies at 28 weeks of gestation and later gave birth in Sweden from 1990 to 2011; 1,804,442 pregnancies were analyzed. In each parity group, the risk of stillbirth at age 30-34 years, 35-39 years, and 40 years and older compared with age 25-29 years was investigated by logistic regression analyses adjusted for sociodemographic factors, smoking, body mass index, history of stillbirth, and interdelivery interval. Also, two low-risk groups were investigated: women with a high level of education and nonsmoking women of normal weight.
Results: Stillbirth rates increased by maternal age: 25-29 years 0.27%; 30-34 years 0.31%; 35-39 years 0.40%; and 40 years or older 0.53%. Stillbirth risk increased by maternal age in first births. Compared with age 25-29 years, this increase was approximately 25% at 30-34 years and doubled at age 35 years. In second, third, and fourth birth or more, stillbirth risk increased with maternal age in women with a low and middle level of education, but not in women with high education. In nonsmokers of normal weight, the risk in second births increased from age 35 years or older and in third births or more from age 30 years or older.
Conclusion: Advanced maternal age is an independent risk factor for stillbirth in nulliparous women. This age-related risk is reduced or eliminated in parous women, possibly as a result of physiologic adaptations during the first pregnancy.
Level of evidence: II.