Birthweight and Chemotherapy Exposure in Women Diagnosed with Breast Cancer during Pregnancy.

OBJECTIVE  Breast cancer is one of the most frequently diagnosed cancers in pregnancy and is commonly treated with chemotherapy. To date, studies examining effects of chemotherapy during pregnancy on fetal growth have yielded conflicting results, and most are limited by small sample sizes or are nonspecific with respect to cytotoxic regimen or type of cancer treated. We sought to evaluate the effect of chemotherapy for breast cancer in pregnancy on birthweight and small for gestational age infants. STUDY DESIGN  This is a retrospective cohort study of 74 women diagnosed with pathologically confirmed breast cancer during pregnancy between 1997 and 2018 at one of three academic medical centers, who had a singleton birth with known birthweight. Forty-nine received chemotherapy and 25 did not receive chemotherapy. Linear regression modeling was used to compare birthweight (by gestational age and sex-specific z-score) by chemotherapy exposure. Subanalyses of specific chemotherapy regimen and duration of chemotherapy exposure were also performed. Placental, neonatal, and maternal outcomes were also analyzed by chemotherapy exposure. RESULTS  In the adjusted model, chemotherapy exposure was associated with lower birthweight (∆ z-score =  - 0.49, p = 0.03), but similar rates of small for gestational age (defined as birthweight <10th percentile for gestational age) infants (8.2 vs. 8.0%, p = 1.0; Fisher's exact test). Each additional week of chemotherapy (∆ z-score =  - 0.05, p = 0.03) was associated with decreased birthweight, although no association was found with specific chemotherapy regimen. Chemotherapy exposure was associated with lower median placental weight percentile by gestational age (9th vs. 75th, p < 0.05). Secondary maternal outcomes were similar between the group that did and did not receive chemotherapy. CONCLUSION  Chemotherapy for breast cancer in pregnancy in this cohort is associated with lower birthweight but no difference in the rate of small for gestational age infants. KEY POINTS · Chemotherapy for breast cancer in pregnancy is associated with decreased birthweight but similar rates of small for gestational age infants.. · Birthweight did not differ according to chemotherapy regimen.. · There is no difference in the rate of small for gestational age infants..