Repeated Measurement of Crown-Rump Length at 9 and 11-13 Weeks' Gestation: Association with Adverse Pregnancy Outcome

Aims: To clarify whether ultrasonographic measurements of crown-rump length (CRL) at 11-13 weeks - based on the number of gestational days determined using the CRL at 9 weeks - can predict fetal prognosis. Methods: A prospective cohort study was conducted to evaluate the association between fetal growth in the first trimester and fetal prognosis. Fetal growth in the first trimester was evaluated measuring CRLs at 11-13 weeks determined using the CRL at 9 weeks. The subjects were divided into short CRL (s-CRL) and normal CRL (n-CRL). The prognoses were compared between the two groups. Results: A total of 126 patients in the s-CRL group and 1,130 patients in the n-CRL group were enrolled. Abortion occurred in 7.1% of s-CRL and 0.9% of n-CRL subjects (p < 0.001). Among the patients with chromosomal abnormalities, the incidence of trisomy 18 was significantly greater in s-CRL (4.8 vs. 0.1%, p < 0.001). Without abortion, placental weight, frequency of small for gestational age (SGA) and birth weight in s-CRL were significantly higher than those in the n-CRL group (12.8 vs. 3.6%, p < 0.001). Conclusions: Measuring CRL at 9 weeks is useful for determining gestational days prior to measuring CRL at 11-13 weeks. After reconfirming the gestational age at 9 weeks, measuring CRL at 11-13 weeks is useful for predicting the incidence of trisomy 18 as well as SGA later in pregnancy.