Trends in Twin Birth Outcomes and Prenatal Care Utilization in the United States, 19811997

1
Trends in Twin Birth Outcomes and Prenatal Care
Utilization in the United States, 1981-1997

• Michael D. Kogan, PhD
• Greg R. Alexander, MPH, ScD
• Milton Kotelchuck, PhD MPH
• Marian F. MacDorman, PhD
• Pierre Buekens, MD
• Joyce A. Martin, MPH
• Emile Papiernik, MD

2
Introduction

• The U.S. preterm and low birthweight rates have
  increased since the mid-1980s
  
• Adequate prenatal care utilization has also
  increased
  
• Additionally, the percent of women receiving more
  than the recommended number of prenatal visits
  has increased

3
Introduction (continued)

• Until recently, most studies have asserted a
  positive association between increasing levels of
  PNC utilization and reduced LBW and preterm
  birth.
• However, the parallel rise in preterm births and
  intensive utilization have led some to question
  the benefits of PNC.

4
Introduction (continued)

• Increase in preterm birth rates may be due to
• An increase in multiple births
• An increased use of ultrasound
• Changes in the limits of fetal viability
• More aggressive management of high-risk
  pregnancies

5
Introduction (continued)

• Significant increase in intensive utilization
  among women having multiple births a high-risk
  subgroup.
  
• Multiple births account for 3 of births in the
  US, but
  
• 21 of all LBW
• 14 of preterm births
• 13 of infant deaths

6
Study Objectives

• Present trends in birth outcomes for twins in the
  U.S.
  
• Explore the hypothesis that more aggressive
  management of multiple pregnancies may be
  associated with changes in birth outcomes.

7
Methods

• Data Sources
• US natality files from 1981-1997
• US linked birth-infant death cohorts (1983-84,
  1989-90, 1995-96)
  
• Twin births only (N 1,479,862)
• Adequacy of prenatal care utilization measured by
  R-Gindex

8
Outcome Measures

• Trends in
• Preterm birth (
• Low birthweight (
• Preterm small for gestational age
• Term small for gestional age
• Infant mortality

9
Percentages of Preterm Birth and Low Birthweight,
1981-97
10
Percentages of Total Preterm Birth and Low
Birthweight from Twin Births, 1981-97
Year
14.3 15.5 16.9 19.1
8.3 9.3 10.9 13.0
11
Percentages of Preterm SGA and Term SGA, 1981-97
12
Twin Infant Mortality Rate, 1983-1996
Year
Twin IMR (per 1000 live twin births)
54.0 47.8 39.9 30.0 -44.4
1983 1987 1991 1996 Change in rates 1981-97

13
Intensive PNC Utilization among Singletons and
Multiples, 1981 and 1996
14
Preterm Birth Rate per 100 Live Twin Births by
Level of PNC Utilization, 1981-1997
15
Intensive PNC Utilization and Twin Preterm Birth,
by Length of Gestation, 1981 and 1997
16
Percentages of Twin Births Delivered Preterm with
Induction of Labor by Level of PNC Utilization,
1989-91 to 1995-97
17
Percentages of Twin Births Delivered Preterm by
First Cesarean Section by Level of PNC
Utilization, 1989-91 to 1995-97
Level of PNC Utilization
Preterm and First Cesarean Section
1995-97
1992-94
Intensive Adequate 24.1 24.7 16.1 22.6
23.4 23.8 15.6 21.5
18
Percentages of Twin Births Delivered Preterm
without Procedures, 1989-91 to 1995-97
Level of PNC Utilization
Preterm without Procedures
1995-97
1992-94
Intensive Adequate 24.1 27.9 21.1 25.5
23.7 28.3 22.3 25.7
19
Odds Ratios for Preterm Twin Births Among
Intensive, Adequate and PNC Comparing 1981, 1990, and 1997
20
Infant Mortality Rates per 1000 Live Births Among
Twins by PNC Level and Gestational Age, 1983-84
21
Infant Mortality Rates per 1000 Live Births Among
Twins by PNC Level and Gestational Age, 1989-90
Less than Adequate
Intensive
Total
Adequate
l
IMR
157.8 10.3 5.8 22.1
233.1 11.2 5.3 43.4
263.2 20.6 11.4 48.5
232.8 13.2 7.7 41.1
22
Infant Mortality Rates per 1000 Live Births Among
Twins by PNC Level and Gestational Age, 1995-96
Less than Adequate
Intensive
Total
Adequate
l
IMR
108.0 7.2 5.4 17.8
173.4 8.2 3.9 33.0
190.6 14.4 6.9 32.8
166.5 9.0 5.1 29.2
23
Conclusions

• Notable increase in preterm and preterm SGA among
  US twin births
  
• Increase has been more marked among women with
  intensive PNC utilization
  
• Increase in preterm has occurred among twins
  delivered with induction of labor or first
  cesarean delivery
  

24
Conclusions (continued)

• Almost all the increase has been among infants
  32-36 weeks
  
• During same period was a major decrease in term
  SGA and in the twin IMR
  

25
Conclusions (continued)

• Changes in obstetric practice and interventions
  may be partly responsible for the increasing twin
  preterm rate
  

26
Conclusions (continued)

• Possible Explanations
• Belief that maturation process of twin births is
  accelerated
  
• Earlier detection of problems requiring early
  intervention, i.e. detection of IUGR
  
• Marker for access to tertiary care facilities
  with NICUs equipped to care for preterm births
  

27
Limitations

• No information on content of PNC
• Incomplete information on possible confounders,
  such as pregnancy complications or STDs
  
• Questions on accuracy and completeness of
  reporting on vital records
  

28
Final Point

• Association between PNC and birth outcomes is far
  more complex than the idea that more PNC leads to
  improved birth outcomes