First-trimester embryo size discordance: a predictor of premature birth following multifetal pregnancy reduction

Abstract

Objective: We have previously reported a correlation between the starting number of embryos for multifetal pregnancy reduction (MFPR) and discordance in size during the first trimester. Here we evaluated the correlation between the degree of discordance and length of gestation in the remaining fetuses. Design: Observational clinical series. Setting: Academic medical center with a single physician who performs a large number of MFPRs. Patient(s): Analysis of 252 consecutive MFPRs from a 2.5-year period (1996–1998). Intervention(s): MFPR for patients with multifetal pregnancies. Main Outcome Measure(s): We evaluated the correlation between the degree of discordance in embryo size, as measured by the greatest difference in crown-rump length (CRL) (Δ max), and the length of gestation. Result(s): Embryo size discordance was related to length of gestation of the remaining fetuses after MFPR. Of 72 patients with a Δ max >5 mm, the rate of severe premature birth (delivery at <28 weeks’ gestation) was 9.7%, compared with 1.7% for patients with a Δ max <5 mm ( P<.01). Of patients with severe premature birth, 70% had Δ max >5 mm, compared with less than 30% in patients who delivered after 28 weeks ( P<.05). Conclusion(s): Variations in embryo growth patterns in multifetal pregnancies may be observed even in the first trimester, which may be predictive of late pregnancy outcomes. With a Δ max ≥5 mm, there is a significant increase in the risk of severe premature birth (delivery at <28 weeks).