Paolo Ivo Cavoretto, M.D., Ph.D., Antonio Farina, M.D., Ph.D., Serena Girardelli, M.D., Gerarda Gaeta, M.D., Silvia Spinillo, M.D., Danila Morano, M.D., Ph.D., Silvia Amodeo, M.D., Alessandro Galdini, M.D., Paola Viganò, Ph.D., Massimo Candiani, M.D.
To compare first-trimester fetal crown-rump length (CRL) measurements in pregnancies obtained after thawed blastocyst transfer versus fresh blastocyst transfer after in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI).
Prospective longitudinal cohort study of CRL Z scores with adjustment for major confounders.
University-affiliated obstetrics, fetal medicine, and fertility units.
Singleton gestations conceived via IVF/ICSI and fresh or thawed blastocyst transfer with ultrasound performed at 6–14 weeks of gestational age.
Main outcome measure(s)
CRL Z scores.
A total of 365 IVF/ICSI pregnancies were recruited (fresh: 161; thawed: 204). The mean CRL Z score at 6–14 weeks was significantly greater in thawed versus fresh transfers. Different growth trajectories between thawed and fresh transfers were detected: Mean CRL Z score was 0 at 65 days in fresh versus 80 days in frozen. Comparisons of both fresh and thawed transfers with reference values from the general population confirmed significantly lower CRL Z scores in both IVF/ICSI groups (P<.001). The risks of CRL <5th percentile in fresh versus thawed were, respectively 68% vs. 40% at 6 weeks and 2% vs. 1% at 14 weeks. A significant positive correlation between CRL Z scores and birth weight Z scores was found only for fresh transfers, not for thawed.
At 6–14 weeks, thawed blastocyst transfers after IVF/ICSI conceptions present greater CRLs compared with fresh, and both IVF/ICSI groups show smaller CRLs than the general population. This effect is particularly evident before 9 weeks and it may favor birth weight difference of thawed versus fresh BT pregnancies.