To compare the birth weight (BW) of largest prior vaginal delivery versus the index pregnancy with shoulder dystocia (SD). From three centers, births with SD were identified and compared to the largest birth weight of prior delivery at term. Among 304 patients, the mean difference in the BW of those with SD in the index pregnancy and largest prior vaginal delivery was 394 ± 510g (p<.0001). The mean differences in BW of those with dystocia and subsequent brachial plexus injury (BPI; 614 ± 569g) versus those without BPI (384.1 ± 508.3g) were also significantly different (p=0.016). There are significant birth weight differences between current and prior birth weight as a predictor of shoulder dystocia with/without BPI. Unfortunately, these findings cannot be used clinically because of the inaccuracy of estimating birth weight.
Shoulder dystocia (SD) is defined as difficulty with delivery, marked by a shoulder-head interval of >1 min or as need for ancillary maneuvers to free the shoulder and occurs in 0.2-3% of vaginal births [
Retrospective studies have identified risk factors for shoulder dystocia, but such risk factors have such a low positive predictive value(<18%) they are not useful clinically in a index pregnancy. [
The purpose of this retrospective, multi-center study was to describe a cohort of parous parturients with shoulder dystocia is the index pregnancy versus the heaviest birth weight of prior newborn without dystocia or BPI, and to contrast parous parturients with a shoulder dystocia in the current gestation who had delivered a fetus ≥4,000 g compared to those who had not.
Over a five year, in three tertiary centers, ICD-9 codes were used to document all parous patients who had shoulder dystocia with or without BPI. In addition, labor/delivery and operating room scheduling books were interrogated to insure that no patient with this diagnosis had been omitted. Finally, newborn records from the same time period were scanned to insure diagnostic accuracy to detect BPI following shoulder dystocia. From the records at each center we investigated the birth weight and obstetric history of the prior vaginal birth, as well as the index newborns’ weight, which was complicated by shoulder dystocia. Additionally, we obtained the antepartum and intrapartum characteristics of the index pregnancy, the maneuvers used to resolve shoulder dystocia and whether the index newborn sustained any injury.
The inclusion criteria for this study using our database were women with prior vaginal delivery at term, know birth weight of prior siblings and shoulder dystocia with the index (current) pregnancy. Twin pregnancy and cesarean section delivery without at least one vaginal term birth were excluded as were anomalous fetuses. The study was approved by Institutional Review Board at two centers and exempted from another.
Along with odds ratio (OR) and 95% confidence intervals (CI), Mann-Whitney or unpaired t-test were used where appropriate. P<0.05 and CI not crossing integer 1 were considered significant.
Over a five year period there were 624 SD in the database, and 304 (49%) met the inclusion criteria and are the focus of the study. Only 3% (10/304) of the cohort had prior SD and none of them had a newborn with brachial plexus injury (BPI). The mean difference in the prior largest and the current BW with SD was 394 ± 510 g heavier. In the index pregnancy, 10% had instrument assisted vaginal birth, 7% (20/304) BPI, and 3% (10/304) a fracture of the clavicle or humerus (
As noted on
Previously, 17% (54/301) of the cohort had delivered a macrosomic fetus vaginally and yet 30% (16/54) had SD with neonates that weighed <4,000 g in the index case (
Backward stepwise logistic regression indentified that the five significant risk factors for BPI among parous parturients: 1) African American race (as compared to Caucasian) (OR 4.69; 95% CI 1.25- 17.56); 2) use of epidural anesthesia (OR 6.95; 95% CI 1.66-29.07); 3) use of suprapubic pressure, (OR 6.42; 95% CI 1.33-31.0); 4) extraction of the posterior arm (OR 9.30; 95% CI 2.07-41.82) and 5) birth weight difference between the previous largest newborn and index pregnancy of 725 g or more (OR 4.10, 95% CI 1.41-11-91).
There are three principal findings in our study. First, only 3% (10 out of 304) had a prior shoulder dystocia among women who delivered a baby complicated by shoulder dystocia in the index pregnancy. None of the infants with a prior shoulder dystocia had brachial plexus injury whereas 7% (20/304) had BPI and 3% (10/304) had fracture of the clavicle or humerus in the index pregnancy. Surprisingly, there were no differences in prior largest birth weight between those who had shoulder dystocia plus BPI (3496 ± 483, p=.704). Likewise, birth weight >4000 gm was also not significantly different amongst the group with BPI compared to the group of patients with shoulder dystocia without BPI (p=.113). Between the two groups, the percent with a difference in birth weights of >10% were higher when the heaviest baby was the prior delivery (p=.024,
Group I |
Group II |
P/ |
|
Age | 27.3 ± 5.3 | 29.5 ± 1.2 | 0.011^ |
Gestational age (weeks) | 39.4 ± 1.1 | 39.1 ± 1.2 | 0.166^ |
Prior Largest (BW grams●) | 3428 ± 448 | 3945 ± 381 | < 0.0001* |
Prior shoulder dystocia | 2% (4) | 10% (6) | 0.16 (0.04, 0.59) |
Diabetes - gestational or pregestational | 7% (17) | 8% (5) | 0.88 (0.31, 2.49) |
Induced/Augmented | 68% (163) | 93% (42) | 1.04 (0.58, 188) |
Epidural | 62% (149) | 63% (40) | 0.93 (0.36, 2.32) |
Spontaneous vaginal delivery | 90% (216) | 90% (57) | <0.0001* |
Birth weight (g) | 4013 ± 428 | 3635 ± 395 | <0.0001^ |
Prior largest BW- |
333 ± 617 | -273 ± 310 | <0.0001^ |
Maneuvers |
1.7 ± 0.8 |
1.5 ± 0.7 |
0.215 |
Three maneuvers or more | 13% (32) | 8% (5) | 1.78 (0.66, 4.76) |
Fracture - clavicle or humerus | 4% (9) | 2% (1) | 2.40 (0.29, 19.36) |
Brachial plexus injury | 7% (18) | 3% (2) | 2.46 (0.56, 19.91) |
Data as mean ± standard deviation or % (n) •BW = birth weight in grams
^Mann-Whitney test used (failed normality test) *Unpaired t-test
Prior BW ≥ 4,000 g |
Prior BW ≤ 3,999 g |
P / |
|
---|---|---|---|
Age | 30.1 ± 6.2 | 27.2 ± 5.3 | 0.002^ |
Gestational age (weeks) | 39.4 ± 1.1 | 39.3 ± 1.1 | 0.880^ |
Prior Largest (BW grams●) | 4222 ± 206 | 3390 ± 388 | <0.0001^ |
Prior shoulder dystocia | 13% (7) | 1% (3) | 12.58 (3.14, 50.45) |
Diabetes - gestational or pregestational | 6% (3) | 8% (19) | 0.88 (0.31, 2.49) |
Induced/Augmented | 66% (35) | 68% (170) | 0.93 (0.49, 1.73) |
Epidural | 68% (36) | 61% (153) | 1.36 (0.72, 2.54) |
Spontaneous vaginal delivery | 94% (50) | 89% (223) | 2.09 (0.61, 7.15) |
Birth weight (g) |
4179 ± 511 |
3883 ± 417 |
<0.0001* |
Prior largest BW - |
-66 ± 493 | 264 ± 627 | <0.004* |
% Difference | -2.4 ± 12.6% | 12.0 ± 11.7% | <0.0001* |
Maneuvers | 1.7 ± 0.9 | 1.6 ± 0.8 | 0.824* |
Three maneuvers or more | 17% (9) | 11% (28) | 1.63 (0.72, 3.69) |
Fracture - clavicle or humerus | 6% (3) | 3% (7) | 2.09 (0.52, 8.37) |
Brachial plexus injury | 6% (3) | 7% (17) | 0.82 (0.23, 2.93) |
Data as mean ± standard deviation or % (n) •BW = birth weight OR = odds ratio; CI = confidence intervals
^Mann-Whitney test used (failed normality test) *Unpaired t-test
Shoulder dystocia |
Shoulder dystocia |
P / |
|
Age | 28.0 ± 4.7 | 27.7 ± 5.6 | 0.685^ |
Gestational age (weeks) | 39.1 ± 1.2 | 39.6 ± 1.1 | 0.460^ |
Prior Largest (BW grams●) | 3496 ± 486 | 3538 ± 483 | 0.704* |
Prior shoulder dystocia | 0 | 4% (10) | 0.64 (0.03, 11.28) |
Diabetes – gestational or pregestational | 25% (5) | 6% (17) | 5.23 (1.70, 16.12) |
Induced/Augmented | 85% (17) | 66% (188) | 2.89 (0.82, 10.12) |
Epidural | 85% (17) | 61% (172) | 3.69 (1.06, 12.89) |
Spontaneous vaginal delivery | 70% (14) | 91% (259) | 0.22 (0.08, 0.64) |
Birth weight (g) |
4110 ± 514 |
3922 ± 441 |
0.113^ |
Current BW |
614.5 ± 569.7 80% (16) | 384.1 ± 508.3 49% (139) | 0.016^ 4.17 (1.36, 12.79) |
% Difference |
14.1 ± 14.9% |
9.2 ± 12.9% |
0.024^ |
Maneuvers |
2.5 ± 0.9 |
1.6 ± 0.8 |
0.004^ |
Three maneuvers or more | 40% (8) | 10% (29) | 5.86 (2.21, 15.52) |
Fracture – clavicle or humerus | 35% (7) | 1% (3) | 50.44 (11.68, 217.76) |
Data as mean ± standard deviation or % (n) •BW = birth weight OR = odds ratio; CI = confidence intervals
^Mann-Whitney test used (failed normality test) *Unpaired t-test
Secondly, when comparing those where the index pregnancy with shoulder dystocia was the heaviest newborn (Group I) versus those where previous was the heaviest (Group II) the rate of recurrent shoulder dystocia was significantly higher in those in Group I versus Group II (2% vs 10%, OF 0.16, 95 CI 0.04, 0.59). Both these findings taken together would indicate that the previous birth weight, whether shoulder dystocia was present or not, cannot be successfully used to predict shoulder dystocia and/or BPI injury in the current or index pregnancy. This is not surprising as even the majority of infants with macrosomia will not develop shoulder dystocia or have BPI [
Lastly, using stepwise logistic regression there were five significant factors for BPI amongst the parturient. First, shoulder dystocia but not BPI, has been noted to be more common in African American patients [
Extraction of the posterior arm during a shoulder dystocia is a known risk factor for BPI [
Similarly, the birth weight difference between the largest previous newborn and the index pregnancy is unable to be used prospectively to predict BPI or shoulder dystocia. Obviously, the birth weight of the index pregnancy is not known until after delivery therefore, it cannot be used as a reliable risk factor because the previous pregnancy had no shoulder dystocia. Perhaps in those women a prior shoulder dystocia was present, and in a gestation where the index pregnancy is believed to be >4500 gms for a diabetic gravida (>5000 gms in euglycemic pregnancies), there might be a place for this factor to be used clinically [
In conclusion, the previous birth weight in parous women who have a shoulder dystocia, is associated with several risk factors for SD in future gestations. However, we have not been able to show that any of these factors are clinically useful on a prospective basis in a future pregnancy.