Original Article

Journal of Perinatology (2006) 26, 392–402. doi:10.1038/sj.jp.7211528

The impact of the interaction between increasing gestational age and obstetrical risk on birth outcomes: evidence of a varying optimal time of delivery

J M Nicholson1,2, L C Kellar1,2 and G M Kellar3

  1. 1Department of Family Medicine and Community Health, University of Pennsylvania Health System, Philadelphia, PA, USA
  2. 2Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Medical Center, Philadelphia, PA, USA
  3. 3Business School, Penn State University – Delaware County, Media, PA, USA

Correspondence: Dr J Nicholson, Department of Family Medicine and Community Health, 2 Gates, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA. E-mail: james.nicholson@uphs.upenn.edu

Received 6 June 2005; Revised 7 April 2006; Accepted 12 April 2006.

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Abstract

Objective:

 

To estimate the gestational age ranges that result in optimal birth outcomes for each of four risk-defined groups.

Study Design:

 

Retrospective cohort study of singleton late third-trimester deliveries at a large urban teaching hospital between July 1995 and September 2003. Low-risk, advanced maternal age, hypertensive and diabetic patients were identified and grouped. Rates, by day of gestation at delivery, of cesarean delivery, major maternal perineal trauma, low 5-min APGAR score and NICU admission were determined for each study group.

Results:

 

Each study group had meaningful changes in rates of obstetric outcomes as a function of gestational age at delivery and these patterns differed from group to group. A unique optimal time of delivery (OTD) was estimated for each group. The low-risk group OTD was calculated to be 37 weeks 1 day to 41 weeks 0 day; the advanced maternal age group OTD was 38 weeks 5 days to 39 weeks 6 days; the hypertension group OTD was 39 weeks 2 days to 40 weeks 1 day; and the diabetes mellitus group OTD was 40 weeks 3 days to 41 weeks 1 day.

Conclusions:

 

The OTD varied based on obstetrical risk. Strategies to increase the proportion of deliveries that occur within the OTD for specific risk-defined groups could theoretically improve birth outcomes.

Keywords:

gestational age, birth outcomes, cesarean delivery, NICU admission, obstetrical risk, optimal time of delivery

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