Second-trimester cordocentesis and the risk of small for gestational age and preterm birth.

OBJECTIVE

To estimate the association of cordocentesis with small for gestational age, preterm birth, and low birth weight.

METHODS

A cohort study from a tertiary care center. Pregnant women without medical or obstetric complications and without ultrasonographically evident fetal anomalies scheduled for cordocentesis between 16 and 22 weeks of gestation (predominantly to detect severe fetal hemoglobinopathies) were prospectively enrolled and matched to a similarly healthy control group on a one-to-one basis by maternal age, parity, gestational age. and ethnicity. In the cordocentesis group, pregnancies found to be complicated by a fetal hemoglobinopathy or a karyotypic abnormality were excluded. Both groups were followed until delivery. The primary outcomes included the rates of small-for-gestational-age preterm birth and low birth weight and fetal loss.

RESULTS

In total, 7,228 women underwent cordocentesis, of whom 5,506 qualified as cases. Of these, 5,039 were matched to women in the control group and had complete outcome data available for the pair. The rates and relative risks (RRs) of small for gestational age (6.9% compared with 4.6%; RR 1.5, 95% confidence interval [CI] 1.3-1.8), preterm birth (12.7 compared with 7.4%; RR 1.7, 95% CI 1.5-1.9), and fetal loss (1.9% compared with 1.0%; RR 1.9, 95% CI 1.4-2.7) were significantly higher among fetuses in the cordocentesis group. However, there were no significant differences in other obstetric complications between the study and control groups.

CONCLUSION

Rates of small for gestational age, preterm birth, low-birth weight, and fetal loss are increased among pregnancies with cordocentesis in the second trimester.