Does low-molecular-weight heparin influence fetal growth or uterine and umbilical arterial Doppler in women with a history of early-onset uteroplacental insufficiency and an inheritable thrombophilia? Secondary randomised controlled trial results.

Objective: Does low-molecular-weight heparin (LMWH) added to low-dose aspirin influence fetal growth and flow velocity in uterine and umbilical arteries in women with an inheritable thrombophilia and previous early-onset uteroplacental insufficiency?

Design: Secondary outcomes of the FRUIT-RCT.

Setting: Multicentre, international.

Population: The FRUIT-RCT included 139 women with inheritable thrombophilia before 12 weeks of gestation. Inclusion criteria were previous delivery before 34 weeks of gestation with a hypertensive disorder of pregnancy and/or small-for-gestational-age infant and an inheritable thrombophilia.

Methods: After randomisation to either daily LMWH with aspirin, or aspirin only, ultrasound measurements were performed at 22-24, 28-30 and 34-36 weeks of gestation. Development during gestation of growth, birthweight and flow velocity of the umbilical artery was examined using the linear mixed model. Uterine artery flow velocity at a single time-point (22-24 weeks) was examined using a chi-square test.

Main Outcome Measures: Fetal growth over time including birthweight, using Scandinavian, Dutch and customised growth curves; and flow velocity within the uterine and umbilical arteries.

Results: No difference of fetal growth over time could be demonstrated between the study arms, regardless of which reference criteria were used. The flow velocity within the uterine artery and umbilical artery did not differ between study arms.

Conclusion: The addition of LMWH to aspirin did not influence fetal growth or umbilical artery flow velocity over time; nor did it influence uterine artery flow velocity.

Tweetable Abstract: LMWH does not influence fetal growth or uterine or umbilical flow velocities.