SAN ANTONIO — Pregnancies in women with a history of breast cancer should be considered high risk on the basis of their increased rates of preterm birth, cesarean section, and congenital malformations, Dr. Kristina Dalberg said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.
One-fifth of women with breast cancer are diagnosed before age 50, and the incidence is increasing. So data on the reproductive impact of the malignancy and its adjuvant therapies are increasingly important, noted Dr. Dalberg of Uppsala (Sweden) University Hospital.
She and her coworkers conducted a Swedish national population-based cohort study in which they cross-checked the 2,870,932 singleton births entered into the Swedish Birth Registry during 1973–2002 against enrollees in the Swedish Cancer Registry database. In this way they identified 331 first births following treatment for invasive breast cancer. The mean time between breast cancer surgery and pregnancy was 37 months.
The former breast cancer patients were significantly older: a mean age of 34 years, compared with 27 years for pregnant women without such a history. Multiple logistic regression analysis adjusted for maternal age, parity, and year of delivery demonstrated that former breast cancer patients had a 3.2-fold increased risk of preterm delivery before 32 weeks, a 2.9-fold increased risk of low birth weight less than 1,500 g, and a 1.3-fold increased rate of C-section, compared with mothers without a history of breast cancer. (See chart below.)
Moreover, women with a history of breast cancer who gave birth during 1988–2002 had a 2.1-fold greater risk of having a baby with congenital malformations than did matched controls. During 1973–1987, when the use of adjuvant chemotherapy in younger breast cancer patients was less common, there was a nonsignificant 1.3-fold increased risk. There was no increase in stillbirths among women with prior breast cancer.
Dr. Dalberg said she and her coinvestigators had hypothesized wrongly that there would be no increased risk of adverse birth outcomes in Swedish women previously treated for breast cancer. This expectation was based in part on a reassuring recent Danish cohort study that showed no increase in preterm birth, low birth weight, congenital malformations, or stillbirth in 216 Danes with previously treated breast cancer (Br. J. Cancer 2006;94:142–6).
The discrepancy might be a result of different ways of classifying outcomes in the two national registries or differences in the use of adjuvant therapies. Additional studies in other countries are needed to resolve the discrepancy. Dr. Dalberg noted that most births in women previously treated for breast cancer are uncomplicated.
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