September 23, 2017 September 23, 2017

The Ten Inch Rule: How Safe are Airbags During Pregnancy?

As you know, airbags can save lives in car crashes, but many of my pregnant patients are very concerned about the risks involved to their unborn child if an airbag is deployed in an accident. Their concerns are warranted in that motor vehicle accidents present a greater risk to a fetus than to infants, or children. Why? Because while a child is vulnerable, that same child is physically independent from the mother. The fetus, on the other hand, relies on the placental connection for blood circulation which in turn provides all nourishment and oxygen necessary for survival in the womb. Any interruption or impairment of that connection places the fetus at high risk. While the uterine environment provides some protection to the fetus, we must remember that the fetus is living and totally dependent.

Unfortunately, motor vehicle accidents (MVA) are the leading cause of fetal trauma in pregnant women, often resulting in fetal and maternal death. Approximately 2.8% of all pregnant women are involved in a motor vehicle accident, with the youngest age groups most affected. Reports of MVAs in pregnancy carries the risks of placental abruption (most common), low birth weight, prematurity resulting from premature labor, premature rupture of the membranes with loss of amniotic fluid and fetal death resulting from the direct trauma. Additionally, poor developmental outcomes, later in the child's life, may be linked to the original trauma from a MVA.

One of our previous blogs discussed the use of seat belts and the evidence that suggests that seat belt use in pregnancy adds substantial protection to both fetus and mom. The American College of Obstetrics and Gynecology confirms improved safety of pregnant women wearing properly positioned seat belts. This newsletter will discuss the use of airbags, because knowing the optimal way to protect a pregnant woman in a car crash is of paramount importance.

Airbags and the ten inch rule

Airbags have now become standard in all automobiles and have been reported to reduce death in non-pregnant motorists. However, the effect of airbags on those positioned too close to the airbag, such as children younger than twelve years of age, infants with rear facing car seats, the elderly, and short women can result in increased injuries and death. To avoid airbag injury, the National Highway and Traffic Safety Association recommends a minimum of a 10 inch distance from the center point of the airbag cover, (the plastic piece facing the driver) which is located either in the steering wheel or the dashboard, depending on the car model.

The safety and efficacy of airbags for pregnant women has not been clearly demonstrated. Since the gravid abdomen can be the leading point of contact from an airbag, especially in the second half of pregnancy, concerns about placental abruption, uterine rupture and direct fetal injury have been raised. It is extremely difficult to comply with the 10 inch safety distance from the airbag to the gravid abdomen, especially in the third trimester of pregnancy. However, it is still felt by the NHTSA that the use of airbags far outweigh the risks.

A recent study by Dr. Melissa Schiff in the January, 2010 article in Obstetrics and Gynecology, found no increased risk of maternal or fetal outcomes in front seat motorists involved in car collisions in which airbags were deployed. However, several other reports have demonstrated the reverse. Dr. Fusco, in the Journal of Trauma 2001, described a case of uterine rupture and fetal demise in a motor vehicle accident, possibly secondary to airbag deployment. Other reports (Schultze, 1998, Pearlman, 1996) described a case of placental abruption with fetal death associated with airbag deployment in a head-on crash. It is difficult to ascertain whether the impact of the collision or the airbag deployment is the cause of the uterine rupture or abruption. We must recall that there is a trade-off. Airbags may protect the mother from serious injury upon any impact with the dashboard or steering wheel.

Why is natural protection not enough protection?

Protection of the fetus from injury relies primarily on the cushioning effect of the amniotic fluid, the thick uterine musculature and the bony supporting structure of the pelvis. However, in a MVA, the placenta does not have the resilience to expand, contract and rapidly change shape with the traumatized rapidly shape-changing uterus, which explains why a shearing effect abruption occurs with rapid acceleration and deceleration forces. Obviously, crash severity affects the generation of fetal injury, but even relatively minor accidents, with speeds as low as 5 miles per hour can be associated with severe fetal trauma when the airbag is deployed at the standard expansion rate of 125 miles per hour.

Seat belts are still the first line of defense

While further research needs to be done to support a definitive statement on the safety of airbags for the pregnant woman and the fetus, the best advice for now is to keep your belly at least 10 inches from the airbag cover, if possible. It is known, however, that shoulder and lap restraints prevent ejection from the car and forward movement of the mother in a front or rear-end collision, and therefore decrease maternal mortality and protect the fetus.

Make sure your seat belt is fastened. Unfortunately, there still exists a substantial group of pregnant women who do not wear seat belts, and when worn, do not wear them properly. Make sure your seat belt is positioned correctly. Seat belts decrease force transmission to the gravid uterus, but airbag deployment might contribute towards increasing force transmission to an anterior placenta resulting in an abruption, uterine rupture, brain hemorrhage, and skull fractures with consequent fetal demise. Another possibility includes the sheer impact of the collision causing these complications. Generally a protocol of monitoring a pregnant patient for at least 4 to 6 hours after a MVA has been adopted by most medical centers to detect whether traumatic injury to the fetus has occurred, as signs can be very subtle.

More research needs to be done that takes into account the gestational age of the fetus, the force of the collision, location of the placenta, and whether a seat belt was used in conjunction with the airbag. A definitive statement will have to await the outcome of such a  future study. I sincerely hope that my readers will be educated by this article and exercise caution, particularly in the second half of pregnancy. In other words, buckle up, remember the ten inch rule and please DRIVE CAREFULLY!