Effects of parity on preterm delivery in twin gestations conceived with in vitro fertilization.

OBJECTIVE

To determine the relationship between prior obstetrical history and gestational age at delivery in a twin pregnancy.

DESIGN

Retrospective cohort study using the United States Society for Assisted Reproductive Technology Clinic Outcomes Reporting System database.

SETTING

Clinic-based data.

PATIENTS

Patients undergoing in vitro fertilization (IVF) in the United States with live delivery of twins.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The main outcome measures are median gestational age at delivery and rate of preterm delivery (before 37 weeks).

RESULTS

The median gestational age at delivery of IVF-conceived twins was 36.3 (interquartile rate 34.4, 37.6) weeks for nulliparous women, 35.9 (34.0, 37.1) weeks for parous women with a prior preterm birth, and 36.7 (35.1, 37.7) weeks for parous women without a prior preterm birth. The rate of preterm delivery was 61% for nulliparous women, 70% for parous women with a prior preterm birth, and 55% for parous women without a prior preterm birth.

CONCLUSIONS

Parous women without a history of preterm delivery had lower rates of preterm delivery in a subsequent twin pregnancy than nulliparous women. Nulliparous women had lower rates of preterm delivery compared with parous women with a history of preterm delivery.