Forty Weeks and Beyond: Pregnancy Outcomes by Week of Gestation JAMES M. ALEXANDER, MD, DONALD D. MCINTIRE, PhD, AND KENNETH J. LEVENO, MD Objective: To assess pregnancy outcomes at 40, 41, and 42 weeks’ gestation when labor induction is done routinely at 42 but not 41 weeks. Methods: We reviewed all singleton pregnancies delivered at 40 or more weeks’ gestation between 1988 and 1998 at Parkland Memorial Hospital, Dallas, Texas. We excluded women with hypertension, prior cesarean, diabetes, malformations, breech presentation, and placenta previa. Labor characteristics and neonatal outcomes of pregnancies at 41 and 42 weeks’ gestation were compared with pregnancies that ended at 40 weeks. Women with certain dating criteria had induction of labor at 42 weeks. Gestational age was calculated from the last menstrual period (LMP), sonography when available, and clinical examination. If the fundal height between 18 and 30 weeks was within 2 cm of gestational age, the reported LMP was accepted as correct. Sonogram was used to calculate gestational age if a discrepancy was identified. Statistical analysis consisted of ␹2 and analysis of variance. Results: We studied 56,317 pregnancies: 29,136 at 40 weeks, 16,386 at 41 weeks, and 10,795 at 42 weeks. Labor complications increased from 40 to 42 weeks, including oxytocin induction (2% versus 35%, P < .001), length of labor (5.5 ⴞ 4.9 versus 8.8 ⴞ 6.5 hours, P < .001), prolonged second stage of labor (2% versus 4%, P < .001), forcep use (6% versus 9%, P < .001), and cesarean delivery (7% versus 14%, P < .001). Neonatal outcomes were similar in the three groups, including 5-minute Apgar score less than 4, admission to the neonatal intensive care unit (NICU), umbilical artery pH less than 7, seizures, and perinatal mortality. Sepsis was more frequent in the 42-week group than the other groups (0.1 versus 0.3%, P ⴝ .001), as was admission to the NICU (0.4 versus 0.6%, P ⴝ .008). Conclusion: Routine labor induction at 41 weeks likely increases labor complications and operative delivery without significantly improving neonatal outcomes. (Obstet Gynecol 2000;96:291– 4. © 2000 by The American College of Obstetricians and Gynecologists.)

From the Department of Obstetrics and Gynecology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas.

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Historically, the concept of an upper limit of human pregnancy duration was based on increases in perinatal mortality in pregnancies that went beyond their expected due date.1 Since the 1970s, a gradual increase in labor induction and more widespread use of antepartum fetal testing has decreased perinatal mortality in pregnancies that reached 42 weeks’ gestation.1 Currently, ACOG recommends labor induction at 42 weeks in women with favorable cervices and cervical ripening and fetal surveillance in women with unfavorable cervices, but recognizes that management of women beyond 40 completed weeks of gestation is unclear.2 The purpose of this study was to assess pregnancy outcomes when labor induction was done routinely at 42 weeks, but not at 41 weeks.

Materials and Methods Obstetric and neonatal outcomes for women who deliver at Parkland Hospital in Dallas are entered in a computerized data base. Nurses present at deliveries complete data sheets that are checked by research nurses for consistency and completeness before electronic storage. Data on infant outcomes are abstracted from discharge records. Parkland Hospital is a taxsupported institution serving Dallas County. The obstetric service is staffed by house officers and faculty of the Department of Obstetrics and Gynecology at the University of Texas Southwestern Medical School. Between January 1, 1988, and December 31, 1998, 82,835 women delivered at or after 40 week’s gestation. We excluded women with hypertension (n ⫽ 7852), prior cesarean deliveries (n ⫽ 4693), diabetes (n ⫽ 1110), fetal malformations (n ⫽ 793), breech presentation (n ⫽ 1812), and placenta previa (n ⫽ 32). Among multiparas, one randomly selected delivery was selected for analysis. Gestational age was calculated from ultrasound results if done, and last menstrual period (LMP) if the

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fundal height between 18 and 30 weeks’ gestation was within 2 cm of the LMP gestational age.3 Women whose fundal heights did not correlate with gestational age had obstetric ultrasonography. Obstetricians’ estimates of gestational ages and pediatricians’ estimates were within 2 weeks of each other in 90% of cases.4 Neonatal outcomes included death before 28 days of age, 5-minute Apgar scores less than 4, and umbilical artery (UA) blood pH of 7.0 or less. Umbilical cord blood was drawn in all cases for measurement of pH. Morbidity included seizures during the 24 hours after birth, admission to the neonatal intensive care unit (NICU), and sepsis diagnosed from positive blood or cerebral spinal fluid cultures. In women with certain gestational ages, we induced labor with oxytocin at the completion of 42 weeks. We prescribed intracervical dinoprostone 0.5 mg the evening before labor induction, regardless of cervical dilatation. Women who did not deliver with the first inductions had second inductions within 3 days. Gestational age was considered certain if the LMP agreed with an ultrasound done before 26 weeks, fundal height measurement between 18 and 30 weeks was within 2 cm of gestational age, or fetal heart sounds were auscultated with a fetoscope between 17 and 20 weeks. Women with uncertain 42-week pregnancies were examined weekly without intervention unless fetal condition was indicated (clinical or sonographic evidence of decreased amniotic fluid [AF] volume or maternal perception of decreased fetal motion). Outpatient fetal heart rate (FHR) testing was not done. Labor induction was done for maternal or fetal indications in women without spontaneous labor or ruptured membranes. Labor augmentation was used when spontaneous labor was ineffective or premature membrane rupture had occurred. Ineffective labor was diagnosed in women with internal uterine pressure monitoring whose cervices did not dilate in 2 to 4 hours. Oxytocin was prescribed at 6 mU per minute and increased by 6 mU per minute every 40 minutes to a maximum of 42 mU per minute.5 Dystocia was diagnosed if labor did not progress after 2 to 4 hours of 200 or more Montevideo units of uterine activity. Statistical analysis included comparisons between groups of women at 40, 41, and 42 weeks’ gestation. ␹2 test was used to compare proportions, and analysis of variance was used for continuous variables. When data were statistically significant, multiple comparisons were done using the Tukey-Kramer procedure to assign which pairwise differences were significant. P ⬍ .05 was statistically significant, tests were two-sided, and analysis was done with SAS, version 6.12 statistical software (SAS Institute, Cary, NC).

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Table 1. Demographics Weeks gestation

Maternal age (y) ⱕ 15 ⱖ 35 Nulliparous Race Hispanic Black White Other

42 n ⫽ 10,795 (%)

40 n ⫽ 29,136 (%)

41 n ⫽ 16,386 (%)

744 (3) 1061 (4) 11,481 (39)

382 (2) 608 (4) 7387 (45)

270 (3) 347 (3) 4931 (46)

16,825 (58) 7231 (25) 4183 (14) 897 (3)

10,362 (63) 3334 (20) 2180 (13) 492 (3)

6485 (60) 2269 (21) 1772 (16) 269 (2)

P .35 .07 ⬍ .001 ⬍ .001

Results Data on 57,507 singleton infants were available for analysis. Table 1 contains demographic characteristics for women who delivered at 40, 41, and 42 weeks. A few of those women (n ⫽ 1190) delivered at 43 weeks and were not included in the analysis. Maternal age distributions at extremes of reproductive life were not related significantly to weeks of gestation at delivery. Nulliparas more often delivered at 41 and 42 weeks compared with 40 weeks, and more Hispanic women delivered at 41 or 42 weeks’ gestation. Demographic differences are summarized in Table 1. All labor characteristics were related significantly to delivery at 40, 41, or 42 weeks’ gestation (Table 2). Labor induction increased significantly between 40 and 42 weeks, and admission to delivery intervals greater than 10 hours and prolonged second stages of labor increased from 40 to 42 weeks. The method of delivery was related significantly to week of gestation, with Table 2. Labor Characteristics Weeks gestation 42 41 40 n ⫽ 29,136 n ⫽ 16,386 n ⫽ 10,795 (%) (%) (%) Oxytocin induction Chorioamnionitis Admission to delivery (hr)* ⬎ 10 hr Second stage labor ⬎ 2 hr Forceps Cesarean Total Dystocia Nonreassuring fetal heart rate

P

688 (2) 1465 (5) 5.5 ⫾ 4.9

1111 (7) 1457 (9) 6.6 ⫾ 5.3

3769 (35) 998 (9) 8.8 ⫾ 6.5

⬍ .001 ⬍ .001 ⬍ .001

4426 (15) 612 (2)

3527 (22) 511 (3)

3859 (36) 378 (4)

⬍ .001 ⬍ .001

1770 (6)

1229 (8)

956 (9)

⬍ .001 ⬍ .001

1924 (7) 1103 (4) 652 (2)

1652 (10) 939 (6) 563 (3)

1540 (14) 974 (9) 460 (4)

* Mean ⫾ standard deviation.

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Table 3. Perinatal Outcomes Weeks gestation 42 41 40 n ⫽ 29,136 n ⫽ 16,386 n ⫽ 10,795 (%) (%) (%)

P

Birth weight (g) Mean ⫾ SD 3393 ⫾ 432 3495 ⫾ 443 3541 ⫾ 453 ⬍ .001 ⬎ 4000 2415 (8) 2028 (12) 1620 (15) ⬍ .001 5-minute Apgar ⬍ 4 61 (0.2) 31 (0.2) 30 (0.3) .29 Umbilical artery blood 91 (0.3) 59 (0.4) 45 (0.4) .34 pH ⱕ 7.0 Admission to intensive 109 (0.4) 85 (0.5) 64 (0.6) .006 care Sepsis* 37 (0.1) 20 (0.1) 30 (0.3) .001 Seizures in first 24 hr 34 (0.1) 24 (0.1) 22 (0.2) .12 Stillbirth 45 (0.2) 22 (0.1) 17 (0.2) .84 Neonatal death 6 4 6 (0.1) .17 SD ⫽ standard deviation. * Positive blood or cerebrospinal fluid culture.

increased operative vaginal delivery and cesareans seen at 41 and 42 weeks. The increased cesarean rates could be attributed to dystocia and nonreassuring FHR. Infant outcomes are summarized in Table 3. Birth weight increased significantly from 40 to 42 weeks. Five-minute Apgar scores less than 4 and fetal acidemia (pH less than 7.0) were not related significantly to gestational age. The NICU admission rate increased slightly from 40 to 42 weeks. Sepsis also was increased significantly but slightly at 42 weeks. Seizures, stillbirth, and neonatal death were not associated significantly with week of gestation at delivery.

Discussion We examined pregnancy outcomes at 40, 41, and 42 weeks in women without confounding variables such as hypertension, diabetes, prior cesarean birth, noncephalic presentation, fetal malformations, or placenta previa. Labor complications increased progressively from 40 to 42 weeks’ gestation, including length of time in labor and need for operative delivery. Infant outcomes were not different, with the exception of an approximately one per thousand births increase in admission to NICU and a two per thousand increase in neonatal sepsis at 42 weeks. Many practitioners induce labor in pregnancies that reach 41 weeks; however, our data suggest that routine intervention then would likely increase labor complications (longer labors, increased operative deliveries) with little or no infant benefit. There is little evidence in the literature to support labor induction or fetal testing at 41 rather than 42 weeks, and no randomized trial has addressed the subject adequately. Two studies randomized women at 41 weeks to labor induction versus fetal testing.6,7 Both

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studies had limitations in methods, including small samples, and neither was able to find an advantage of one intervention over the other. Three earlier randomized trials compared labor induction at 40 versus 42 weeks.9,10 Only one of these three studies found a benefit of labor induction that was limited to less frequent meconium-stained AF. No randomized study to date has indicated that fetal testing or labor induced at 40 or 41 weeks’ gestation changes or improves neonatal outcomes significantly. A national policy of routine intervention at 41 weeks would affect approximately 500,000 women per year. We believe interventions at 41 weeks’ gestation are unwarranted because of a lack of proven benefit and would result in increased labor complications and health care costs in a significant number of women. Larger randomized studies must be done before labor induction is done routinely in pregnancies that reach 41 weeks.

References 1. Cunningham FG, MacDonald PC, Gant NF, Leveno KJ, Gilstrap LC III, Hankins GDV, et al. Postterm pregnancy. In: Licht J, Broadhurst B, eds. Williams obstetrics. 20th ed. Stamford, Connecticut: Appleton and Lange, 1997;827–37. 2. American College of Obstetricians and Gynecologists. Management of postterm pregnancy. ACOG Practice Patterns no. 6. Washington, DC: American College of Obstetricians and Gynecologists, 1997. 3. Jimenez JM, Tyson JE, Reisch JS. Clinical measures of gestational age in normal pregnancies. Obstet Gynecol 1983;61:438 – 43. 4. McIntire DD, Bloom SL, Casey BM, Leveno KJ. Birthweight in relation to morbidity and mortality among newborn infants. N Engl J Med 1999;340:1234 – 8. 5. Satin AJ, Leveno KJ, Sherman ML, McIntire DD. High-dose oxytocin: 20- versus 40-minute dosage interval. Obstet Gynecol 1994; 83:234 – 8. 6. Hannah ME, Hannah WJ, Hellmann MB, Hewson S, Milner BA, Willan A, et al. Induction of labor as compared with serial antenatal monitoring in postterm pregnancy: A randomized trial. N Engl J Med 1997;326:1587–92. 7. The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. A clinical trial of induction of labor versus expectant management in postterm pregnancy. Am J Obstet Gynecol 1994;170:716 –23. 8. Husslein P, Egarter C, Sevelda P, Genger H, Salzer H, Kofler E. Induction of labour with prostaglandin E2 vaginal tablets: A revival of elective induction. Results of a randomized trial. Geburtshilfe Frauenheilkd 1986;46:83–7. 9. Martin DH, Thompson W, Pinkerton JHM, Watson JD: A randomized controlled trial of selective planned delivery. Br J Obstet Gynaecol 1978;85:109 –13. 10. Tylleskar J, Finnstrom O, Leijon I, Hedenskop S, Ryden G. Spontaneous labour and elective induction—A prospective randomized study. 1. Effect on mother and fetus. Acta Obstet Gynecol Scan 1979;59:513– 8.

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James M. Alexander, MD Department of Obstetrics and Gynecology University of Texas Southwestern Medical Center at Dallas 5323 Harry Hines Boulevard Dallas, TX 75235-9032 E-mail: [email protected]

NEW,

Received August 27, 1999. Received in revised form February 17, 2000. Accepted March 9, 2000.

Copyright © 2000 by The American College of Obstetricians and Gynecologists. Published by Elsevier Science Inc.

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