Open Journal of Obstetrics and Gynecology, 2011, 1, 202-207
doi:10.4236/ojog.2011.14039 Published Online December 2011 ( OJOG
Published Online December 2011 in SciRes.
Motor-Vehicle crashes during pregnancy: a retrospective
cohort study
Harold B. Weiss1,2, Erin K. Sauber-Schatz1,3, Amy H. Herring4
1University of Pittsburgh, Department of Neurological Surgery, Center for Injury Research and Control, Pittsburgh, USA (At the time
of study);
2University of Otago, Department of Preventive and Social Medicine, Injury Prevention Research Unit, Dunedin, New Zealand
3Centers for Disease Control and Prevention, National Center for Injury Research and Control, Division of Unintentional Injury,
Atlanta, USA (Currently);
4Department of Biostatistics and Carolina Population Center, The University of North Carolina, Chapel Hill, USA.
Received 8 October 2011; revised 17 November 2011; accepted 2 December 2011.
Background: The purpose of this study was to assess
the risk of motor-vehicle pregnant driver crashes in
Pennsylvania using vital statistics linked to police
and ambulance reports. This was supplemented with
a review of national age and sex specific crash and
fertility data to put this risk into perspective and
rank the likelihood for pregnancy-related crashes in
other states. Methods: Motor vehicle police crash re-
ports from the Pennsylvania Department of Trans-
portation were probabilistically linked to four years
of birth and fetal death data and five years of infant
death records and ambulance reports. State specific
motor-vehicle traffic injury rates (fatal and non-fa-
tal) were compared to birth rates, by age, for wo-
men ages 15 - 34. Results: 5929 (1.1%) of the wo-
men with a birth or fetal death linked to a police
reported motor vehicle driver crash during preg-
nancy. One-third (32.5%) of these crashes resulted
in minor maternal injuries and 7.5% resulted in mo-
derate to fatal maternal injuries. Crashes were even-
ly distributed across gestational ages. Young drivers
(20 - 24) were at highest risk. Police reported non-
belt use was 10%. Conclusions: This study quantifies
the risk of motor vehicle crashes during pregnancy
in Pennsylvania and offers a perspective on poten-
tial variations in other states. Pregnancy related cra-
shes occur at a higher rate than infant related cra-
shes with a concomitant threat to the fetus and new-
born not usually tracked within current crash data
Keywords: Maternal Injury; Moto r Vehicle Crash
As the infectious scourges of childbirth during the early
part of the 20th century yielded to advances in modern
health care, women of reproductive age began to take to
the road in motor vehicles as never before. The resulting
changes in pregnancy-associated mortality and morbid-
dity have led to motor-vehicle related injuries becoming
the leading cause of maternal death during pregnancy [1,2 ],
the leading cause of hospitalized maternal trauma during
pregnancy [3-5], for the fetus the leading cause of trau-
matic fetal injury mortality [6], and in 2007 the leading
cause of childhood injury death for children aged 3 and
older [7]. It has been shown that there are more fetal
deaths due to maternal crashes than there are infant
deaths in motor vehicle crashes [2].
The ubiquity of motor-vehicle travel by pregnant wo-
men, in combination with their crash risk, has led to re-
ports from national sample surveys that about 2% - 3%
of all live births in the U.S. are annually exposed in-
utero to a police-reported crash [8]. This means about
100,000 children (rate = 26/1000 person-years) in the
United States (US) may be annually exposed in-utero to
the direct and indirect impact of a motor-vehicle crash.
For comparison, NHTSA reports that there were an es-
timated 58,606 infants in crashes in 2008 [9]. Fetal mo-
tor-vehicle (MV) crashes have probably increased sub-
stantially over the last two decades primarily because
more women are driving and driving more miles [10].
Other health sciences that study human exposure to
toxic, infectious, and radiologic agents pay a great deal
of attention to in-u tero exposure, a known critical p eriod
in human development. With few exceptions, however, th e
injury field has not. This paper uses a probabilistic ma-
tching study to characterize the number of pregnancy re-
H. B. Weiss et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 202-207 203
lated crashes in one state. It is supplemented with a re-
view of national age and sex specific crash and fertility
data to rank the likelihood for pregnancy-related crashes
in other states.
We used a retrospective cohort design approved by the
University of Pittsburgh Institutional Review Board. I-
dentifying pregnant drivers in crashes was achieved by
probabilistically linking records from several different
databases (police crash reports, births, fetal deaths and
ambulance run reports) using common variables to deter-
mine the probability that two records referred to the sa-
me person and/or event. To identify cases for which the
crash occurred during pregnancy, the following case se-
lection was applied: If the gestational age (in weeks) at
birth or fetal death was available, we looked back in time
for a crash event within the gestational age plus one week.
If only the date of last menses was noted and the date of
last menses occurred after the woman’s reported crash the
case was excluded. The few records without any indica-
tion of gestational age or last menses were excl uded.
Our aim was to link four years of Pennsylvania birth
and fetal death data (2002-2005) with drivers in crashes
along with any available matching ambulance run re-
ports. Ambulance run reports allowed for more specific
crash severity and other injury information than police
reports. Only drivers were included in the study because
Pennsylvania crash data, like most states, only contains
the names of drivers, making linkage to passengers pro-
blematic. However, previous work has shown that about
70% of pregnant women in crashes are the driver [8]. In
order to avoid misclassification of crash exposure, for
infants born in 2002 or infant deaths of infants born in
2005, crash data from 2001 and infant death data for
2006 were linked to 2002-2005 birth, crash, fetal and
infant death data.
Linkage was performed using Automatch software
(2008, Strategic Matching, Inc). In order to keep linkage
quality high, a priori criteria were established for sele-
cting matched cases. Using the software, we aimed for
90% specificity and 95% sensitivity for the crash to the
birth and fetal death linkage and 90% specificity and
90% sensitivity for the crash to EMS linkage. By ad-
ministrative fiat from the Department of Transportation
we were not allowed to use the existing social security
numbers to link driver records with birth data. However,
names (sometimes only initials), maternal birth dates and
addresses were usually available for the crash driver to
vital statistics linkage and therefore adequate linkage
could be accomplished. The analytical team only recei-
ved de-identified data as an honest broker (Strategic Ma-
tching, Inc.) performed all data linkage. For rate calcula-
tions, in the rare event that more than one crash occurred
during the same pregnancy only the data for th e most se-
vere crash was includ ed.
We identified 5929 registered births and fetal deaths
from 2002-2004 linking to a female driver crash report.
Among these linked cases, about a third (31.7%) were
linked to an EMS run report (n = 1878). Of the total
birth outcomes, 5885 were live births and 44 were fetal
deaths. With 562,993 birth and fetal deaths reported for
2002-2004 this results in a maternal crash rate (crashes
among all reported pregnancies) of 1.1%. A small num-
ber of mothers were identified with multiple crashes;
1.5% (n = 91) had two crashes and two had three crashes
during the same pregnancy. For all pregnancy-related
crashes, the mean age of the mother at the time of the
infants birth was 26.9 years (range 14 to 51). Figure 1
Figure 1. Mothers age at birth or fetal death in pregnancy related driver crashes, Pennsylvania, 2002 to
opyright © 2011 SciRes. OJOG
H. B. Weiss et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 202-207
Figure 2. Gestational age in weeks of fetus at time of maternal crash, Pennsylvania, 2002 to 2005.a (a. Excludes 130 cases
with missing gestational age).
shows the frequency of all the first crashes by maternal
age. The age-specific rate of maternal crashes per 1000
live births was highest among mothers ages 20 - 24 at
1.34 crashes per 1000 live births. Other rates per 1000
live births were as follows: 15 years - 19 years = 1.19,
25 years - 29 years = 1.03, 30 year s - 34 years = 0.82, 35
years - 39 years = 0.78, and 40 years - 44 years = 0.67.
Police reported injury severity indicated that 48.3% of
the pregnant women drivers in a crash were not injured,
32.5% had a minor injury, 7.5% had a moderate or major
injury and one fatality was reported. Crashes were more
likely to occur on a weekday than a weekend. Weekday
crashes ranged fr om 15.0% on Monday to 17.8% on Fr i-
day with Saturday and Sunday crashes accounting for
10.7% and 8.5%, respectively. Collision angles were mo-
stly either frontal (35.8%) or a rear-end collision (34.2%).
Most maternal crashes (82.1%) had no contributing en-
vironmental crash factors (such as rain or snow) reported,
but 7.8% indicated slip pery conditions at the time of the
crash. Most crashes occurred during daylight hours (76.4%)
and involved hitting another veh icle or being hit by ano-
ther vehicle. Crashes occurred predominantly in urban
areas (79.6%).
Rollovers occurred in 2.6% of the crashes. Most cra-
shes involved sedans (83.7%, including station wagons)
and SUV’s (8.5%). The mean travel speed upon impact
was reported by police as 27.5 miles per hour (MPH),
ranging from 0 to 97 MPH. Among the one-third of the
cases that linked to a matching EMS run report, 16.4%
were reported to be in crashes with a change in velocity
of greater than 20 MPH and 44% received some kind of
basic life support treatment while 15.1% received some
type of advanced life support treatment.
Police reported 10% non-belt use and 16.6% unknown
belt use status. In the subset of 1.878 cases that matched
to an EMS report, reported non-belt use rate was 13.3%
(this included situations where only a lap belt or shou-
lder belt was worn). Airbags were reported by the police
to have deployed in 17.1% of all crashes and by EMS
personnel in 19.2% of the crashes linked to ambulance
Suspected alcohol or drug involvement was reported
by the police in 1.3% of th e cases. Two-thirds of the dri-
vers (67.8%) were reported by the police to be transpor-
ted to a medical facility though this does not necessarily
mean transport by emergency medical services. Among
the EMS cases, 80% were reportedly transported to a
medical facility.
Approximately a third of the crashes occurred in each
trimester; 35.0% the first trimester, 34.7% the second,
and 30.3% the third trimester. Figure 2 shows the gesta-
tional age by week of the reported maternal crashes.
This study of motor vehicle crashes during pregnancy in
Pennsylvania has some similarities and differences from
the only other similar study that has been conducted. In a
Utah linkage study for the period 1992 to 1999, it was
reported that 2.8% of the live births experienced a ma-
ternal driver crash [11]. This is over twice as high as
what was found in Pennsylvania. There are several pos-
sible reasons for this difference. It is useful to explore
these reasons to understand how these factors might im-
pact on other states experiences should they want to ex-
plore or conduct similar data linkages for surveillance
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H. B. Weiss et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 202-207 205
From a demographic perspective, assuming for comp-
arative purposes that environmental factors are about e-
qual, maternal crash risk is driven in large part by the fer-
tility of the underlying population (the number of births
per year), the age distribution of the pregnant population,
and the age-specific crash risk of the women of repro-
ducetive age. For example, if the crash rate among young
women is high but the mean age at pregnancy in that
population occurs several years post peak crash risk, this
population will have a lower maternal crash risk than a
group with a similar rate and age distribution of crashes
but a peak pregnancy pattern among y ounger m others.
Figure 3 illustrates this by showing U.S. motor vehi-
cle traffic injury rates (fatal and non-fatal) compared to
birth rates, by age, for women ages 15 - 34. From a na-
tional perspective, it shows th at fatal and non-fatal crash
injury rates follow a similar age-specific pattern for wo-
men of reproductive age. They both rapidly increase at
younger age groups from age 16 and peak at age 18, slo-
wly declining over the next 12 years. With the age-spe-
cific birth rate overlaid on the crash injury pattern, Fi-
gure 3 shows that in the U.S. age-specific birth rates
peak a little later than the crash risk. A different popula-
tion (i.e., a sub-population such as a state or racial/ethnic
group) that had the same age-specific pattern of crash ri-
sk but higher birth rates among younger women would
probably have a higher rate of maternal crashes since
crash injury rates are generally higher in younger women.
So it is useful to observe that there app ears to be a large
variation among states in the fatal crash risk of women
of reproductive age, ranging from 3.7 to 25.8 deaths per
100,000 women age 15 - 34 (see Figure 4) [12].
Figure 3. U.S. motor vehicle traffic injury rates (fatal and non-fatal) compared to birth rates, by age, for women ages
15 - 34.a(a. Fatal rates produced by the Centers for Disease Control and Prevention, National Center for Health Statis-
tics. Compressed Mortality File 1999-2005). CDC WONDER On-line Database, compiled from Compressed Mortality
File 1999-2005 Series 20 No. 2K, 2008. Accessed at on Jun 16, 2009. Non-fatal
(emergency department visits) rates produced by WISQARS nonfatal injury reports from the office of statistics and
programming, National Center for Injury Prevention and Control, CDC. URL:
nfirates2001.html. Data Source: NEISS all injury program operated by the Consumer Product Safety Commission for
numbers of injuries. Bureau of Census for population estimates. Birth rates produced from the National Vital Statistics
System Birth Tables, URL: Bureau of Census for
population estimates.
opyright © 2011 SciRes. OJOG
H. B. Weiss et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 202-207
Figure 4. Scatter plot of mean age of mother at first live birth (2000)a versus the crash fatality rate per 100,000 women of reproduce-
tive age (15 - 34, 1999-2005),b by U.S. state.(a. Mean age of mother at first live birth by State (year 2000), from National Vital Statis-
tics Rep or ts, Vol. 51, No. 1, N ati on al C e nter for H eal th St atis ti cs , 2002 . ( (b. Fatal-
ity data source: Centers for Disease Control and Prevention, National Center for Health Statistics. Compressed Mortality File 1999-2005).
CDC WONDER On-lin e Database; 1999- 2005 Series 20 No. 2K, 2008. Accessed at http://wond Jun 16, 2009.
The only two states studied so far with crash and vital
statistics linkage studies, Utah and Pennsylvania, have
annualized vehicle traffic fatality rates for women of
reproductive age of 10.7 and 10.3 p er 1,000,000 women,
respectively for 1999-2005. But many states have twice
this rate. As age-specific birth and crash rates act toge-
ther, sub-populations can be expected to have very di-
fferent rates of maternal crash involvement. In particular,
states with both a high crash risk among young women
of reproductive age and high birth rates among the same
group of younger mothers would be at especially high
risk of maternal/fetal crash injury.
Figure 4 shows a scatter plot of the mean age of mo-
thers at first live birth by State for the year 2000 [13]
with the motor vehicle traffic fatality rate per 100,000
women ages 15 - 34 for 1999-2005 (which as shown in
Figure 2, correlates well with non-fatal crash injury ra-
tes) [11]. States in the upper left quadrant would be pri-
me jurisdictions to explore whether they truly have ele-
vated maternal crash injury rates. It also suggests that the
rates of maternal crashes observed in Utah and Pen-
nsylvania may be in the lower half of all the states and
the lower rate observed in Pennsylvania compared to
Utah may be due, in part, to the much younger mothers
in Utah since younger women are at a higher risk of
having a crash. It is also possible that successful linkage
rates varied between Pennsylvania and Utah. Similar
linking software and techniques were used, but differen-
ces in available variable types and state specific data co-
llection procedures impacting on linkage quality and com-
pleteness cannot be ruled out.
Over one-third of the cases that linked to an EMS re-
port were reported not to use the full lap/shoulder belt
combination which parallels findings from the Utah stu-
dy showing decreasing belt use as injury severity increa-
sed [11]. This level of misuse is of concern as the Ameri-
can College of Obstetricians and Gynecologists (ACOG)
[14] and others [15] have long recommend the use of sea-
tbelts during pregnancy and many studies have shown
the benefits of seatbelt use [11,16,17]. Unfortunately, our
study had no way to reliably ascertain proper belt use
among the study population .
There were other limitations affecting case ascertain-
ment. Fetal deaths before 20 week gestation are not re-
ported to vital statistics and thus were not available for
linkage. Pregnant women who may have been involved
in a crash but moved out of state or gave birth in another
state would also be missed. Excluding the second and
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H. B. Weiss et al. / Open Journal of Obstetrics and Gynecology 1 (2011) 202-207 207
third crashes for the small number with multiple crashes
also underestimates the overall crash risk. Therefore, the
incidence estimates probably err to the conservative side.
Using probabilistic linkage of crash and vital statistics
records we determined that in Pennsylvania at least 1.1%
of all pregnancies were involved in a driver related mo-
tor vehicle crash with little variance in risk over gesta-
tional age but higher crash rates among younger mothers.
Pennsylvania’s motor vehicle crash rate during pregnan-
cy might be on the lower end of the risk spectrum com-
pared to other states because of relatively older maternal
ages at birth and the overall lower crash injury risk in ol-
der women.
These data, combined with other evidence [2], confi-
rm that pregnancy related crashes occur at a higher rate
than infant related crashes with a concomitant threat to
the fetus and new-born that cannot be tracked within
current crash data systems without on-going data linkage
efforts. The National Highway Traffic Safety Admini-
stration (NHTSA) already has an existing network of
more than a dozen state-based programs that currently
link crash data to ambulance run reports called the Crash
Outcome Data Evaluation System (CODES) [18]. It wou-
ld not take many additional resources for those states to
add linkages to state vital statistics (birth and fetal death)
data, in effect setting up an inexpensive but robust preg-
nancy-related d river crash surveillan ce system for CODES
states. Without such efforts this important threat to the
fetus and newborn cannot be tracked and evaluated, re-
maining a hidden cause of crash injury and mortality to
the very youngest of crash victims.
This work was supported by the Centers for Disease Control and Pre-
vention, National Center for Injury Prevention and Control (grant CCR
323155) at the University of Pittsburgh, Department of Neurological
Surgery, Center for Injury Research and Control. We gratefully ac-
knowledge the assistance of Dr. Michael McGlincy of Strategic Mat-
ching Inc. who served as this study’s honest broker and who performed
all of the probabilistic linkages.
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