Driving Pregnancy Safety and the Seat Belt

Estimated reading time: 13 minutes

A summary of studies regarding driving during pregnancy

We write a lot about pregnancy safety while driving. And we do talk about whether or not just the seat belt is adequate protection for pregnant moms-to-be.

Now don’t get us wrong, we definitely advocate for properly wearing your seat belt during pregnancy for every drive!

We also believe every pregnant woman should be fully informed regarding possible risks and how to best mitigate those risks. That way she and her baby can be as safe as possible.

We mention and cite various studies in all of our articles about driving during pregnancy. Here we wanted to summarize those studies and share some of the most profound findings we attained from each.

The following comments are separated based by category. Each comment is numbered with its corresponding place in the ever growing list of pregnancy and driving studies.

Crashes are leading cause of trauma during pregnancy

“In pregnant women the largest single cause of maternal death is automobile crashes.” 1

Trauma affects between 3% and 7% of all pregnancies in industrialized countries, and the leading cause of these traumas is car crashes. (4)

Motor vehicle collisions are the leading cause of injury during pregnancy, accounting for 60% of injuries. Motor vehicle collisions cause the most severe maternal injuries and fetal death. (9)

How common are crashes involving pregnant women?

79,000 children are exposed in utero to a police-reported crash (police reported crashes only account for 1/3 of all crashes). For comparison, the National Highway Traffic Safety Administration reports that there are only about 23,188 infants reported in crashes each year. (13)

About 6 to 7 percent of women who are pregnant are involved in a car crash during their pregnancy. That translates to about 170,000 car crashes a year involving pregnant women. (16)

Causing fetal loss into the thousands

800 to 3,200 fetuses are killed when the mother survives in the US. (6)

“Several new estimates of the number of fetal losses were made using a variety of approaches based on crash statistics and pregnancy rates. The estimates range from 300 to 3,800 fetal losses per year to women over 20 weeks gestation as a result of maternal involvement in a motor-vehicle crash.” (15)

Based on the frequencies of pregnancies and crash involvement of the general population, it has been estimated that between 1,500 and 5,000 fetal losses occur each year in the United States as a result of maternal involvement in automotive crashes. (9)

The magnitude of the problem is likely far greater than the numbers show, Weiss says, because many cases – especially those involving early pregnancy – are not recorded in a way that is accessible to researchers. (10)

Risk compared to newborn

However, current data shows that risk to the fetus is still elevated on the order of 5 times greater than the risk to a 0 to 1 year old sibling riding in the same car. (12)

Risk of fetus death from traffic crash is 5 times the risk compared to the first 9 months of a baby’s life. This number is based only on the 227 pregnant mothers who died (in which the unborn baby also died) compared to the 60 newborns who died in traffic crashes in 2012. “This ratio likely underestimates the disparity because the risk of crashing is increased during pregnancy and we have ignored the many cases in which the mother survives but the fetus does not,” researchers explained. (25)

Impact in a crash

Two main kinematics events were identified as possible causes of injuries: lap belt loading and backrest impact. (4)

Fetal acceleration in a car crash 3x that of the mother (Thackeray, 2002), offering insight as to the reasons fetus might die as a result of pregnancy-related injuries such as placental abruption or skull injury. (2)

Download our free PDF guide: Safer Driving During Pregnancy

Anatomy of pregnant woman and car crash impact

Seatbelt use during pregnancy creates unique challenges and the potential for directly-transferred energy to the gravid uterus, likely leading to an increased rate of injury and complications to both the mother and unborn fetus. (31)

Early in pregnancy, the uterus remains a pelvic organ and is protected by the bony pelvis, making it less susceptible to blunt trauma. The growing uterus becomes increasingly at risk for trauma as the pregnancy progresses. (2)

Until the 12th week of gestation, the uterus remains a pelvic organ and is protected by the bony pelvis against direct impact. (26)

At 20 weeks, the uterus and head extend forward of the anterior extremis of the pelvis; the baby has no frontal protection at all other than soft abdominal tissues. At 36 weeks, the baby has typically dropped to a head-downward position. The head will eventually be “locked” in the pelvic saddle, and virtually the entire body of the baby other than the top of its head will extend forward and upward of the pelvis. (12)

The side view of the lap belt relative to the pregnant abdomen in Figure 6 illustrates the challenges posed by pregnant anatomy to automotive safety engineers. This subject positioned the belt correctly, and it crossed very close to the left and right ASlS as desired. However, in the midline plane, the lap belt crosses over the protruding pregnant abdomen directly over the uterus. In a crash, the uterus would be loaded before the bony structures. (14)

“When the subjects were instructed to position the lap belt as low as possible beneath their pregnant abdomens, the lap-belt centerline was within +/- 20 mm of the ASIS on most subjects. However even with the lap belt positioned over the bony pelvis, it crossed the pregnant uterus in the mid-sagittal plane at a level corresponding to 50-80% of the total uterus height. This potentially allows loading of the protruding soft tissues of the pregnant abdomen by the lap belt during a frontal impact.” (27)

Other factors to consider in crashes involving pregnant women

In this study, all of the severe crashes had adverse fetal outcomes. Impact direction, occupant seating position, gestational age, maternal stature, and maternal weight do not have statistically significant effects on fetal outcome in this database. (15)

“The effect of trauma on pregnancy depends on the gestational age of the fetus, the type and severity of the trauma and the extent of disruption of normal uterine and fetal physiology.” (26)

Injuries most likely experienced if in a crash while pregnant

“Not surprisingly, the more severe the maternal injury, the greater the likelihood of fetal death. However, even minor maternal injuries can result in the death of the fetus.” (26)

Fetal death can occur even if the mother has no visible injuries. (9)

Placental abruption is the most common cause of fetal loss in automotive crashes. It occurs in 1 to 5% of minor severity crashes during pregnancy and from 20 to 50% of severe crashes during pregnancy. Some placental abruptions may result from high-velocity, low-mass airbag loading, or from compression between the mother’s body and the steering wheel, belt, or instrument panel. “While these results show that placental injuries can occur to properly belted pregnant occupants, they also show that avoiding belt use during pregnancy may significantly increase the risk of placental abruption and subsequent fetal loss in a crash.” (14)

Placental abruption is most frequent cause of fetal death after car crash. Cases of abruption within five days of crash have been reported. (2)

Although crashes involving pregnant women can cause obvious immediate harm, such as placental abruption, uterine rupture, or emergency premature delivery, less is known about delayed effects of motor vehicle crashes on pregnancy outcomes. (13)

Fetal fatality statistics do not include uncounted adverse outcomes from motor vehicle collisions, like:

• Disabilities resulting from in-utero injuries.
• Complications from emergency delivery, such as low birth weight or neonatal respiratory distress syndrome that lead to long-term negative outcomes.
• Low birth weight can lead to a lifetime of possible disabilities and medical problems.
• Neonatal respiratory distress syndrome means breathing difficulty for the neonate because the lungs are not fully developed. (9)

Additional uncounted adverse fetal outcomes occur as well. Many children grow up disabled as a result of injuries sustained in utero. Even if a fetus survives, complications arising from early emergency delivery of a premature fetus (such as low birth weight and neonatal respiratory distress syndrome) can lead to long-term negative consequences for the child. (14)

Restraint usage among pregnant women

This study relied on self-reporting for seat belt use during a crash. Because Utah has a law for mandatory restraint use with secondary enforcement, over reporting of belt use probably occurred. This would result in overstating the protective nature of seatbelts in preventing adverse outcomes. Information was not available on whether or not seatbelts were properly worn (according to recommendations) during pregnancy. (13)

Reasons pregnant women often don’t wear seat belts:

• seat belt was uncomfortable,
• shoulder strap too tight across breasts,
• lap belt tended to slide up over abdomen,
• lap belt too tight or short,
• fear the fetus would be harmed. (2)

Most common reported reasons for pregnant women not wearing a restraint were 52.8% lack of comfort or 42.5% forgetfulness. (30)

Get your guide about safer driving practices for during pregnancy

The submarining effect

Just to note: Read this to understand what submarining is.

Submarining of the occupant in all but lowest belt position subsequently caused large abdominal and uterine compression. (6)

In the common event of submarining, the lap belt penetrates the abdomen and fetus as the legs continue to pull the lower pelvis forward until it penetrates through the fetus’ body to the lumbar spine of the mother. The fetus is trapped between the horizontal lap belt and the vertical lumbar spine. (12)

Effectiveness of current seat belt restraints

Lap belt restraint alone was considered to be appropriate during the 60s and 70s and was associated with a reduction in maternal death from 7.8 to 3.6 percent. However, fetal loss related to car crash increased from 14.4 to 16.7 percent. When lap-only belt is used forced flexion of the maternal body over the belt compresses, bends or twists the gravid uterus, resulting in negative pressure that may cause placental abruption. (2)

“It was shown that the three-point belt and the four-point belt were superior in protecting the pregnant occupant by reducing the movement towards the far side door and therefore eliminating the head strike potential. However, this resulted in some force being applied through the abdomen and, therefore, it increased the risk of fetal injury. This is an acceptable trade-off given the most important factor in saving the fetus’ life is keeping the mother alive.” (7)

“The fact is that it is not possible to position the lap belt in a way that would prevent crushing the fetus in a frontal crash. Clearly lap and shoulder belts alone are not appropriate for use by pregnant women.” (12)

Most basic purpose of using the seat belt is to keep the occupant in the car. Maternal mortality is 33% if the woman is ejected and 5% if not. Fetal mortality is 47% if mom is ejected and 11% if not. (2)

Fetal loss occurred in 12 of 41 properly restrained occupants (29%), in contrast to 3 of the 6 (50%) improperly restrained women. Eight of the ten (80%) unrestrained women had adverse fetal outcomes. (34)

“By using the results shown in Figure 2, the risk of adverse fetal outcome for properly restrained pregnant occupants is less than 10% in minor crashes and more than 60% in severe crashes.” (16)

Improving safety systems for driving pregnancy safety

Development of safety systems specific to the pregnant woman may be possible. (3)

“Given the magnitude and severity of pregnant occupant injuries, this study illustrates the need for manufacturers to consider four-point belt systems for this population.” (29)

No testing method or protocol has been developed to credibly assess the performance of various pregnancy seat belt devices and configurations regarding fetal safety in motor vehicle crashes. (12) (This includes standards being set for just the seat belt in regard to pregnant occupants. While no testing protocols exist, Tummy Shield has been tested to the nearest appropriate protocols available.)

We need to better understand how to protect pregnant women from being in a crash and, if in a crash, how to better protect them. Finally, we need to know much more about the long term developmental, physical, and cognitive consequences on the children who are impacted by this problem so very early in life. (21)

Steve Rouhana, senior technical leader for safety in Ford’s passive safety research and advanced engineering department, says pregnant women should continue using seatbelts until answers are found. “The seatbelt is the best safety device in the vehicle today, but it doesn’t mean we can’t make it better.” (USA Today article)

Increased education needed for driving pregnancy safety

Despite this reported risk and the proven efficacy of restraint use, most pregnant women do not report being counseled about seat belt use during prenatal visits. (22)

“I often look after pregnant women who will ask me about flights and scuba diving and hot tubs and medications and many other things, but I’m almost never asked about vehicle crashes, despite them frequently causing serious injury to mother and baby,” says Donald Redelmeier, a professor of medicine at the University of Toronto and a staff physician at Sunnybrook Health Sciences Centre. (Today’s Parent article)

“Traffic safety is an established part of pediatric care and the low rates of motor vehicle traffic fatalities during infancy indicate that such efforts are effective. The current data highlight that such prevention needs to start even earlier as a part of standard prenatal care. Specifically, pregnant women should be advised by their physicians on the even greater importance of road safety before the baby is born.” (25)

This is our why

Some experts will tell you wearing the seat belt properly while driving during pregnancy is all you need to be adequately protected. After all, car manufacturers and NHTSA say the seat belt is safe and effective as is so it must be true.

We disagree. And we’ve talked with doctors and women — both who used Tummy Shield and who didn’t — who would strongly disagree.

It’s true our company provides the Tummy Shield seat belt repositioner for pregnant women. But that’s not why we disagree. As safety experts, we didn’t decide to provide the Tummy Shield until after a deep dive into the research about pregnancy safety and the seat belt, summarized above.

Some of these studies are also why the Tummy Shield was created. Though for the engineer of the Tummy Shield, the why goes deeper and more personal. Read the Tummy Shield developer’s personal story.

By Amie Durocher, Creative Director at Safe Ride 4 Kids and certified CPS Tech since 2004

Copyright 2023 Safe Ride 4 Kids. All rights reserved. You may not publish, broadcast, rewrite or redistribute this material without permission. You are welcome to link to Safe Ride 4 Kids or share on social media.

Sources:

• Each comment is numbered to the corresponding number on our studies about driving pregnancy safety list. From that list you can find links to each study.