Early ultrasound gestational age dating

We developed the approach and methods using data from the Iowa Health in Pregnancy Study (IHIPS), a population-based case-control study designed to determine the influence of intimate partner violence and maternal stress on the risks of preterm and SGA outcomes among livebirths to residents of 4 Iowa counties during the period May 2002 through June 2005.Using electronic birth certificates as the sampling frame, we selected all Iowa residents of the study counties who delivered a singleton preterm infant ( = 2,709) completed the computer-assisted telephone interview.Because early prenatal care is associated with better recall of LMP and access to early ultrasound, all included subjects had to initiate prenatal care before the 14th completed gestational week.If the LMP date was missing from the medical chart, it was substituted from the birth certificate.Signed medical record releases were received from over 90% of interviewed subjects, and medical chart abstractions were completed for 93.5% ( = 2,308) of medical releases received.To determine whether early ultrasound dating of GA tends to underestimate the duration of gestation among women with suspected SGA infants based on livebirth certificate data, we restricted the analysis to IHIPS case and control subjects who had complete data from computer-assisted telephone interviewing and medical chart abstraction and who met each of the following criteria: 1) first-trimester prenatal care, 2) a nonmissing LMP date, and 3) a first recorded ultrasound examination taken between the 7th and 20th completed weeks of pregnancy.The overall response rate, defined as the proportion of women who consented to screening for the study out of all those who were selected from the birth certificates, was 45.2%.

All data analysis was conducted using SAS software, version 9.2 (SAS Institute Inc., Cary, North Carolina).Reliance on ultrasound dating alone led to an artificially low reported rate of SGA birth and an artificially high rate of PTD (14, 15).In a study of pregnancies conceived by in vitro fertilization (i.e., with an accurate date of conception), fetuses dated as being 5 or 6 days younger by ultrasound at 10–14 weeks’ gestation were substantially more likely to be SGA at delivery (13).The mean days differences for PTD and control subjects were similar: 1.1 days and –0.2 days, respectively.In contrast, the mean days difference for SGA subjects was 5.5 days, which is substantially higher than the days difference observed among control ('s website (

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