Shoulder Dystocia

Shoulder dystocia is a term used to describe difficulty in birthing the shoulders of the baby after the head has emerged. Shoulder dystocia concerns families and caregivers because of its association with nerve injuries or death of the baby and bleeding or lacerations of the mother.

Bigger Babies
Women with exceptionally bigger babies (macrosomia) have a higher risk of experiencing shoulder dystocia. A study done in California (Nesbitt, 1998) reported the percentages of spontaneous births of nondiabetics complicated by shoulder dystocia for different birth weights.

Birth weight (lbs)	8.8 – 9.4	9.4 – 9.9	9.9 - 10.5	10.5 - 11
% of births complicated by shoulder dystocia	5.2%	9.1%	14.3%	21.1%

There is no guarantee that mothers with babies smaller than 8.8 lbs won't have shoulder dystocia. One study (Acker, 1986) found that nearly half of all shoulder dystocia cases occur during births of babies smaller than 8.8 lbs.

Given the correlation with birth weight, caregivers and families often try to predict birth weight in the hope of preventing shoulder dystocia and its complications.

Predicting Baby's Size
Predicting fetal weight by ultrasound or clinical palpation (Leopold’s maneuvers) is imprecise. Our expectation that ultrasound would be more accurate at predicting birth weight than clinical estimates has not been confirmed. One study (Chauhan, 1992) found that a mother's own estimate of birth weight was more likely to be within 10% of the actual birth weight than either a physician's clinical estimate or an ultrasonographic estimate.

Method of estimation	Mother’s estimate	Clinical estimate	Ultrasound estimate
% of estimates within 10% of the actual birth weight	70%	66%	42%

Other Risk Factors
In addition, women with diabetes are also at higher risk for encountering shoulder dystocia during their labor. This risk factor is independent of birth weight (Dildy, 2000).

Most researchers also report an association between shoulder dystocia and operative vaginal delivery (forceps or vacuum extraction). Operative vaginal delivery is also associated with an increased risk of nerve injuries (Belfort, 2007).

What Should We Do?
Despite our current inability to accurately determine baby’s birth weight until after the birth, some caregivers use their best guess and recommend intervention.

Some providers tout early induction as a method to birth a baby before it gets “too big.” Other providers advocate cesarean section for suspected macrosomia as a method to avoid shoulder dystocia. Because these approaches have not been shown to improve outcomes for mother or baby, the American College of Obstetricians and Gynecologists does not recommend induction or cesarean section for all women with suspected macrosomia (ACOG practice bulletin #40).

For non-diabetic women with babies estimated to be over 11 lbs or for diabetic women with babies estimated to be over 9.9 lbs, scheduled cesarean section has not been shown to improve outcomes for either mother or baby. This may be in part due to a trade-off of other risks to mother and baby that increase with cesarean sections. In addition, most cases of shoulder dystocia can be successfully managed without additional injury to baby or mother. ACOG states that scheduled cesarean section may be considered in these cases.

One researcher (Rouse, 1996) calculated that over 1000 cesarean sections would have to be performed in non-diabetic women with suspected macrosomia in order to prevent one nerve injury. In addition, such a policy would have no effect on the almost equally prevalent cases of shoulder dystocia happening with babies that are smaller than 8.8 lbs.

Comments

[Katy Plummer]

Thanks for this informative post. It has been very helpful to both myself and my sister. We grow big babies, and are forever being harassed to book in for a c-section. I think my sister is taking a copy to her next hospital visit! Again, thanks.