First trimester ultrasound screening is effective in reducing postterm labor induction rates: a randomized controlled trial.
OBJECTIVE
This study was designed to test the null hypothesis that first trimester ultrasound crown-rump length measurement for gestational age determination will result in no difference in the rate of induction of labor for postterm pregnancy, compared with second trimester biometry alone.


METHODS
Two hundred eighteen women were randomly assigned to receive either first trimester ultrasound screening or second trimester ultrasound screening to establish the expected date of confinement. Sample size was calculated by using a 2-tailed alpha=.05 and power (1-beta)=80%. Data were analyzed with chi(2) and Fisher exact tests.


RESULTS
Of 104 women randomly assigned to the first trimester screening group, 41.3% had their gestational age adjusted on the basis of the crown-rump length measurement. Of 92 women randomly assigned to the second trimester screening group, 10.9% were corrected as a result of biometry (P <.001, relative risk=0.26, 95% CI=0.15-0.46). Five women in the first trimester screening group and 12 women in the second trimester screening group had labor induced for postterm pregnancy (P=0.04, relative risk=0.37, 95% CI=0.14-0.96).


CONCLUSIONS
The application of a program of first trimester ultrasound screening to a low-risk obstetric population results in a significant reduction in the rate of labor induction for postterm pregnancy.
Bennett
Kelly A
KA
Department of Obstetrics and Gynecology, Vanderbilt University, Nashville, TN 37212, USA. kelly.a.bennett@vanderbilt.edu
Crane
Joan M G
JM
O'shea
Patrick
P
Lacelle
Joanne
J
Hutchens
Donna
D
Copel
Joshua A
JA
D000293:Adolescent; D000328:Adult; D018568:Crown-Rump Length; D005260:Female; D005865:Gestational Age; D006801:Humans; D007751:Labor, Induced / Q000706:statistics & numerical data*; D009523:Newfoundland and Labrador / Q000453:epidemiology; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011273:Pregnancy, Prolonged; D015995:Prevalence; D016896:Treatment Outcome; D016216:Ultrasonography, Prenatal