Fortunately, fetal trauma in pregnancy is uncommon.
The most common causes of blunt fetal trauma, in contrast to penetrating injuries such as stabbings or gunshot wounds, are motor-vehicle collisions, falls and assaults. It has long been taught that if the mother survives injury, the fetus will, too. Maternal death, unless followed in minutes by Caesarian delivery, will result in fetal demise.
Precise data are difficult to collect. Fetal demise often has no standard definition, the cause of death may be unknown or it is omitted in death certificates. An added difficulty is that pregnancy is often unmentioned in accident reporting.
In reality, the fetus is very well-protected in the first trimester, up to 12 or so weeks because the uterus and contents are below the pelvic rim. Risk increases with increasing uterine size. The uterus, quite simply, becomes a larger target for blunt force. With rupture of the uterus, fetal mortality reaches 100 percent, while maternal mortality is less than 10 percent. Rupture is uncommon and represents less than 1 percent of traumatic injuries during pregnancy.
The most common injury in pregnancy is placental abruption – the traumatic separation or tearing away of the placenta from the uterine wall. Because the uterine wall is elastic, it resists tearing. In comparison, the placenta is relatively inelastic and may shear off the uterus, causing hemorrhage and impaired oxygen delivery to the fetus, depending on the degree of separation. Large abruptions are screaming emergencies.
Cranial injuries are the most common direct fetal injury, especially in the third trimester. In the last weeks, the head settles into the pelvis and becomes “engaged,” no longer mobile or floating about. If the maternal pelvis should be fractured, it is bad news for the fetus.
If seat belts and air bags save mothers’ lives, they save babies. However, there are caveats. The lap portion of the belt should be low – not across the abdomen, but across the pelvis. The shoulder belt should cross the sternum between the breasts. The recommended minimum distance from sternum to steering wheel is 10 inches – limiting potential air-bag injury.
On an eastern highway with a two-lane rotary, a woman, a few weeks from her due date, became distracted. She collided with another vehicle almost head-on.
Upon emergency-room arrival, she had obvious left clavicle and left lower leg fractures. The test for amniotic fluid was positive, indicating ruptured membranes. Fetal distress quickly became evident, and persistent seizures occurred after Caesarean delivery.
An ensuing CT scan demonstrated diffuse intra-cerebral bleeding, trauma secondary to the steering wheel. Months later, most of the child’s brain tissue had been replaced with fluid – I’ve never seen worse. Tragically, the “distraction” was the result of the mother’s attempting to latch her seat belt.
Fraser Houston, a retired emergency room physician, worked at area hospitals after moving to Southwest Colorado from New Hampshire in 1990.